| 1 | @page |
| 2 | @node Data Types |
| 3 | @chapter Data Types for Generic Use |
| 4 | |
| 5 | This chapter describes all the data types that Guile provides for |
| 6 | ``generic use''. |
| 7 | |
| 8 | One of the great strengths of Scheme is that there is no straightforward |
| 9 | distinction between ``data'' and ``functionality''. For example, |
| 10 | Guile's support for dynamic linking could be described |
| 11 | |
| 12 | @itemize @bullet |
| 13 | @item |
| 14 | either in a ``data-centric'' way, as the behaviour and properties of the |
| 15 | ``dynamically linked object'' data type, and the operations that may be |
| 16 | applied to instances of this type |
| 17 | |
| 18 | @item |
| 19 | or in a ``functionality-centric'' way, as the set of procedures that |
| 20 | constitute Guile's support for dynamic linking, in the context of the |
| 21 | module system. |
| 22 | @end itemize |
| 23 | |
| 24 | The contents of this chapter are, therefore, a matter of judgement. By |
| 25 | ``generic use'', we mean to select those data types whose typical use as |
| 26 | @emph{data} in a wide variety of programming contexts is more important |
| 27 | than their use in the implementation of a particular piece of |
| 28 | @emph{functionality}. |
| 29 | |
| 30 | @ifinfo |
| 31 | The following menu |
| 32 | @end ifinfo |
| 33 | @iftex |
| 34 | The table of contents for this chapter |
| 35 | @end iftex |
| 36 | @ifhtml |
| 37 | The following table of contents |
| 38 | @end ifhtml |
| 39 | shows the data types that are documented in this chapter. The final |
| 40 | section of this chapter lists all the core Guile data types that are not |
| 41 | documented here, and provides links to the ``functionality-centric'' |
| 42 | sections of this manual that cover them. |
| 43 | |
| 44 | @menu |
| 45 | * Booleans:: True/false values. |
| 46 | * Numbers:: Numerical data types. |
| 47 | * Characters:: New character names. |
| 48 | * Strings:: Special things about strings. |
| 49 | * Regular Expressions:: Pattern matching and substitution. |
| 50 | * Symbols and Variables:: Manipulating the Scheme symbol table. |
| 51 | * Keywords:: Self-quoting, customizable display keywords. |
| 52 | * Pairs:: Scheme's basic building block. |
| 53 | * Lists:: Special list functions supported by Guile. |
| 54 | * Vectors:: One-dimensional arrays of Scheme objects. |
| 55 | * Records:: |
| 56 | * Structures:: |
| 57 | * Arrays:: Arrays of values. |
| 58 | * Association Lists and Hash Tables:: Dictionary data types. |
| 59 | * Hooks:: User-customizable event lists. |
| 60 | * Other Data Types:: Data types that are documented elsewhere. |
| 61 | @end menu |
| 62 | |
| 63 | |
| 64 | @node Booleans |
| 65 | @section Booleans |
| 66 | @tpindex Booleans |
| 67 | |
| 68 | The two boolean values are @code{#t} for true and @code{#f} for false. |
| 69 | |
| 70 | Boolean values are returned by predicate procedures, such as the general |
| 71 | equality predicates @code{eq?}, @code{eqv?} and @code{equal?} |
| 72 | (@pxref{Equality}) and numerical and string comparison operators like |
| 73 | @code{string=?} (@pxref{String Comparison}) and @code{<=} |
| 74 | (@pxref{Comparison}). |
| 75 | |
| 76 | @lisp |
| 77 | (<= 3 8) |
| 78 | @result{} |
| 79 | #t |
| 80 | |
| 81 | (<= 3 -3) |
| 82 | @result{} |
| 83 | #f |
| 84 | |
| 85 | (equal? "house" "houses") |
| 86 | @result{} |
| 87 | #f |
| 88 | |
| 89 | (eq? #f #f) |
| 90 | @result{} |
| 91 | #t |
| 92 | @end lisp |
| 93 | |
| 94 | In test condition contexts like @code{if} and @code{cond} (@pxref{if |
| 95 | cond case}), where a group of subexpressions will be evaluated only if a |
| 96 | @var{condition} expression evaluates to ``true'', ``true'' means any |
| 97 | value at all except @code{#f}. |
| 98 | |
| 99 | @lisp |
| 100 | (if #t "yes" "no") |
| 101 | @result{} |
| 102 | "yes" |
| 103 | |
| 104 | (if 0 "yes" "no") |
| 105 | @result{} |
| 106 | "yes" |
| 107 | |
| 108 | (if #f "yes" "no") |
| 109 | @result{} |
| 110 | "no" |
| 111 | @end lisp |
| 112 | |
| 113 | A result of this asymmetry is that typical Scheme source code more often |
| 114 | uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to |
| 115 | represent an @code{if} or @code{cond} false value, whereas @code{#t} is |
| 116 | not necessary to represent an @code{if} or @code{cond} true value. |
| 117 | |
| 118 | It is important to note that @code{#f} is @strong{not} equivalent to any |
| 119 | other Scheme value. In particular, @code{#f} is not the same as the |
| 120 | number 0 (like in C and C++), and not the same as the ``empty list'' |
| 121 | (like in some Lisp dialects). |
| 122 | |
| 123 | The @code{not} procedure returns the boolean inverse of its argument: |
| 124 | |
| 125 | @rnindex not |
| 126 | @deffn primitive not x |
| 127 | Return @code{#t} iff @var{x} is @code{#f}, else return @code{#f}. |
| 128 | @end deffn |
| 129 | |
| 130 | The @code{boolean?} procedure is a predicate that returns @code{#t} if |
| 131 | its argument is one of the boolean values, otherwise @code{#f}. |
| 132 | |
| 133 | @rnindex boolean? |
| 134 | @deffn primitive boolean? obj |
| 135 | Return @code{#t} iff @var{obj} is either @code{#t} or @code{#f}. |
| 136 | @end deffn |
| 137 | |
| 138 | |
| 139 | @node Numbers |
| 140 | @section Numerical data types |
| 141 | @tpindex Numbers |
| 142 | |
| 143 | Guile supports a rich ``tower'' of numerical types --- integer, |
| 144 | rational, real and complex --- and provides an extensive set of |
| 145 | mathematical and scientific functions for operating on numerical |
| 146 | data. This section of the manual documents those types and functions. |
| 147 | |
| 148 | You may also find it illuminating to read R5RS's presentation of numbers |
| 149 | in Scheme, which is particularly clear and accessible: see |
| 150 | @xref{Numbers,,,r5rs}. |
| 151 | |
| 152 | @menu |
| 153 | * Numerical Tower:: Scheme's numerical "tower". |
| 154 | * Integers:: Whole numbers. |
| 155 | * Reals and Rationals:: Real and rational numbers. |
| 156 | * Complex Numbers:: Complex numbers. |
| 157 | * Exactness:: Exactness and inexactness. |
| 158 | * Number Syntax:: Read syntax for numerical data. |
| 159 | * Integer Operations:: Operations on integer values. |
| 160 | * Comparison:: Comparison predicates. |
| 161 | * Conversion:: Converting numbers to and from strings. |
| 162 | * Complex:: Complex number operations. |
| 163 | * Arithmetic:: Arithmetic functions. |
| 164 | * Scientific:: Scientific functions. |
| 165 | * Primitive Numerics:: Primitive numeric functions. |
| 166 | * Bitwise Operations:: Logical AND, OR, NOT, and so on. |
| 167 | * Random:: Random number generation. |
| 168 | @end menu |
| 169 | |
| 170 | |
| 171 | @node Numerical Tower |
| 172 | @subsection Scheme's Numerical ``Tower'' |
| 173 | @rnindex number? |
| 174 | |
| 175 | Scheme's numerical ``tower'' consists of the following categories of |
| 176 | numbers: |
| 177 | |
| 178 | @itemize @bullet |
| 179 | @item |
| 180 | integers (whole numbers) |
| 181 | |
| 182 | @item |
| 183 | rationals (the set of numbers that can be expressed as P/Q where P and Q |
| 184 | are integers) |
| 185 | |
| 186 | @item |
| 187 | real numbers (the set of numbers that describes all possible positions |
| 188 | along a one dimensional line) |
| 189 | |
| 190 | @item |
| 191 | complex numbers (the set of numbers that describes all possible |
| 192 | positions in a two dimensional space) |
| 193 | @end itemize |
| 194 | |
| 195 | It is called a tower because each category ``sits on'' the one that |
| 196 | follows it, in the sense that every integer is also a rational, every |
| 197 | rational is also real, and every real number is also a complex number |
| 198 | (but with zero imaginary part). |
| 199 | |
| 200 | Of these, Guile implements integers, reals and complex numbers as |
| 201 | distinct types. Rationals are implemented as regards the read syntax |
| 202 | for rational numbers that is specified by R5RS, but are immediately |
| 203 | converted by Guile to the corresponding real number. |
| 204 | |
| 205 | The @code{number?} predicate may be applied to any Scheme value to |
| 206 | discover whether the value is any of the supported numerical types. |
| 207 | |
| 208 | @deffn primitive number? obj |
| 209 | Return @code{#t} if @var{obj} is any kind of number, @code{#f} else. |
| 210 | @end deffn |
| 211 | |
| 212 | For example: |
| 213 | |
| 214 | @lisp |
| 215 | (number? 3) |
| 216 | @result{} |
| 217 | #t |
| 218 | |
| 219 | (number? "hello there!") |
| 220 | @result{} |
| 221 | #f |
| 222 | |
| 223 | (define pi 3.141592654) |
| 224 | (number? pi) |
| 225 | @result{} |
| 226 | #t |
| 227 | @end lisp |
| 228 | |
| 229 | The next few subsections document each of Guile's numerical data types |
| 230 | in detail. |
| 231 | |
| 232 | @node Integers |
| 233 | @subsection Integers |
| 234 | |
| 235 | @tpindex Integer numbers |
| 236 | |
| 237 | @rnindex integer? |
| 238 | |
| 239 | Integers are whole numbers, that is numbers with no fractional part, |
| 240 | such as 2, 83 and -3789. |
| 241 | |
| 242 | Integers in Guile can be arbitrarily big, as shown by the following |
| 243 | example. |
| 244 | |
| 245 | @lisp |
| 246 | (define (factorial n) |
| 247 | (let loop ((n n) (product 1)) |
| 248 | (if (= n 0) |
| 249 | product |
| 250 | (loop (- n 1) (* product n))))) |
| 251 | |
| 252 | (factorial 3) |
| 253 | @result{} |
| 254 | 6 |
| 255 | |
| 256 | (factorial 20) |
| 257 | @result{} |
| 258 | 2432902008176640000 |
| 259 | |
| 260 | (- (factorial 45)) |
| 261 | @result{} |
| 262 | -119622220865480194561963161495657715064383733760000000000 |
| 263 | @end lisp |
| 264 | |
| 265 | Readers whose background is in programming languages where integers are |
| 266 | limited by the need to fit into just 4 or 8 bytes of memory may find |
| 267 | this surprising, or suspect that Guile's representation of integers is |
| 268 | inefficient. In fact, Guile achieves a near optimal balance of |
| 269 | convenience and efficiency by using the host computer's native |
| 270 | representation of integers where possible, and a more general |
| 271 | representation where the required number does not fit in the native |
| 272 | form. Conversion between these two representations is automatic and |
| 273 | completely invisible to the Scheme level programmer. |
| 274 | |
| 275 | @c REFFIXME Maybe point here to discussion of handling immediates/bignums |
| 276 | @c on the C level, where the conversion is not so automatic - NJ |
| 277 | |
| 278 | @deffn primitive integer? x |
| 279 | Return @code{#t} if @var{x} is an integer number, @code{#f} else. |
| 280 | |
| 281 | @lisp |
| 282 | (integer? 487) |
| 283 | @result{} |
| 284 | #t |
| 285 | |
| 286 | (integer? -3.4) |
| 287 | @result{} |
| 288 | #f |
| 289 | @end lisp |
| 290 | @end deffn |
| 291 | |
| 292 | |
| 293 | @node Reals and Rationals |
| 294 | @subsection Real and Rational Numbers |
| 295 | @tpindex Real numbers |
| 296 | @tpindex Rational numbers |
| 297 | |
| 298 | @rnindex real? |
| 299 | @rnindex rational? |
| 300 | |
| 301 | Mathematically, the real numbers are the set of numbers that describe |
| 302 | all possible points along a continuous, infinite, one-dimensional line. |
| 303 | The rational numbers are the set of all numbers that can be written as |
| 304 | fractions P/Q, where P and Q are integers. All rational numbers are |
| 305 | also real, but there are real numbers that are not rational, for example |
| 306 | the square root of 2, and pi. |
| 307 | |
| 308 | Guile represents both real and rational numbers approximately using a |
| 309 | floating point encoding with limited precision. Even though the actual |
| 310 | encoding is in binary, it may be helpful to think of it as a decimal |
| 311 | number with a limited number of significant figures and a decimal point |
| 312 | somewhere, since this corresponds to the standard notation for non-whole |
| 313 | numbers. For example: |
| 314 | |
| 315 | @lisp |
| 316 | 0.34 |
| 317 | -0.00000142857931198 |
| 318 | -5648394822220000000000.0 |
| 319 | 4.0 |
| 320 | @end lisp |
| 321 | |
| 322 | The limited precision of Guile's encoding means that any ``real'' number |
| 323 | in Guile can be written in a rational form, by multiplying and then dividing |
| 324 | by sufficient powers of 10 (or in fact, 2). For example, |
| 325 | @code{-0.00000142857931198} is the same as @code{142857931198} divided by |
| 326 | @code{100000000000000000}. In Guile's current incarnation, therefore, |
| 327 | the @code{rational?} and @code{real?} predicates are equivalent. |
| 328 | |
| 329 | Another aspect of this equivalence is that Guile currently does not |
| 330 | preserve the exactness that is possible with rational arithmetic. |
| 331 | If such exactness is needed, it is of course possible to implement |
| 332 | exact rational arithmetic at the Scheme level using Guile's arbitrary |
| 333 | size integers. |
| 334 | |
| 335 | A planned future revision of Guile's numerical tower will make it |
| 336 | possible to implement exact representations and arithmetic for both |
| 337 | rational numbers and real irrational numbers such as square roots, |
| 338 | and in such a way that the new kinds of number integrate seamlessly |
| 339 | with those that are already implemented. |
| 340 | |
| 341 | @deffn primitive real? obj |
| 342 | Return @code{#t} if @var{obj} is a real number, @code{#f} else. |
| 343 | Note that the sets of integer and rational values form subsets |
| 344 | of the set of real numbers, so the predicate will also be fulfilled |
| 345 | if @var{obj} is an integer number or a rational number. |
| 346 | @end deffn |
| 347 | |
| 348 | @deffn primitive rational? x |
| 349 | Return @code{#t} if @var{x} is a rational number, @code{#f} |
| 350 | else. Note that the set of integer values forms a subset of |
| 351 | the set of rational numbers, i. e. the predicate will also be |
| 352 | fulfilled if @var{x} is an integer number. Real numbers |
| 353 | will also satisfy this predicate, because of their limited |
| 354 | precision. |
| 355 | @end deffn |
| 356 | |
| 357 | |
| 358 | @node Complex Numbers |
| 359 | @subsection Complex Numbers |
| 360 | @tpindex Complex numbers |
| 361 | |
| 362 | @rnindex complex? |
| 363 | |
| 364 | Complex numbers are the set of numbers that describe all possible points |
| 365 | in a two-dimensional space. The two coordinates of a particular point |
| 366 | in this space are known as the @dfn{real} and @dfn{imaginary} parts of |
| 367 | the complex number that describes that point. |
| 368 | |
| 369 | In Guile, complex numbers are written in rectangular form as the sum of |
| 370 | their real and imaginary parts, using the symbol @code{i} to indicate |
| 371 | the imaginary part. |
| 372 | |
| 373 | @lisp |
| 374 | 3+4i |
| 375 | @result{} |
| 376 | 3.0+4.0i |
| 377 | |
| 378 | (* 3-8i 2.3+0.3i) |
| 379 | @result{} |
| 380 | 9.3-17.5i |
| 381 | @end lisp |
| 382 | |
| 383 | Guile represents a complex number as a pair of numbers both of which are |
| 384 | real, so the real and imaginary parts of a complex number have the same |
| 385 | properties of inexactness and limited precision as single real numbers. |
| 386 | |
| 387 | @deffn primitive complex? x |
| 388 | Return @code{#t} if @var{x} is a complex number, @code{#f} |
| 389 | else. Note that the sets of real, rational and integer |
| 390 | values form subsets of the set of complex numbers, i. e. the |
| 391 | predicate will also be fulfilled if @var{x} is a real, |
| 392 | rational or integer number. |
| 393 | @end deffn |
| 394 | |
| 395 | |
| 396 | @node Exactness |
| 397 | @subsection Exact and Inexact Numbers |
| 398 | @tpindex Exact numbers |
| 399 | @tpindex Inexact numbers |
| 400 | |
| 401 | @rnindex exact? |
| 402 | @rnindex inexact? |
| 403 | @rnindex exact->inexact |
| 404 | @rnindex inexact->exact |
| 405 | |
| 406 | R5RS requires that a calculation involving inexact numbers always |
| 407 | produces an inexact result. To meet this requirement, Guile |
| 408 | distinguishes between an exact integer value such as @code{5} and the |
| 409 | corresponding inexact real value which, to the limited precision |
| 410 | available, has no fractional part, and is printed as @code{5.0}. Guile |
| 411 | will only convert the latter value to the former when forced to do so by |
| 412 | an invocation of the @code{inexact->exact} procedure. |
| 413 | |
| 414 | @deffn primitive exact? x |
| 415 | Return @code{#t} if @var{x} is an exact number, @code{#f} |
| 416 | otherwise. |
| 417 | @end deffn |
| 418 | |
| 419 | @deffn primitive inexact? x |
| 420 | Return @code{#t} if @var{x} is an inexact number, @code{#f} |
| 421 | else. |
| 422 | @end deffn |
| 423 | |
| 424 | @deffn primitive inexact->exact z |
| 425 | Return an exact number that is numerically closest to @var{z}. |
| 426 | @end deffn |
| 427 | |
| 428 | @c begin (texi-doc-string "guile" "exact->inexact") |
| 429 | @deffn primitive exact->inexact z |
| 430 | Convert the number @var{z} to its inexact representation. |
| 431 | @end deffn |
| 432 | |
| 433 | |
| 434 | @node Number Syntax |
| 435 | @subsection Read Syntax for Numerical Data |
| 436 | |
| 437 | The read syntax for integers is a string of digits, optionally |
| 438 | preceded by a minus or plus character, a code indicating the |
| 439 | base in which the integer is encoded, and a code indicating whether |
| 440 | the number is exact or inexact. The supported base codes are: |
| 441 | |
| 442 | @itemize @bullet |
| 443 | @item |
| 444 | @code{#b}, @code{#B} --- the integer is written in binary (base 2) |
| 445 | |
| 446 | @item |
| 447 | @code{#o}, @code{#O} --- the integer is written in octal (base 8) |
| 448 | |
| 449 | @item |
| 450 | @code{#d}, @code{#D} --- the integer is written in decimal (base 10) |
| 451 | |
| 452 | @item |
| 453 | @code{#x}, @code{#X} --- the integer is written in hexadecimal (base 16). |
| 454 | @end itemize |
| 455 | |
| 456 | If the base code is omitted, the integer is assumed to be decimal. The |
| 457 | following examples show how these base codes are used. |
| 458 | |
| 459 | @lisp |
| 460 | -13 |
| 461 | @result{} |
| 462 | -13 |
| 463 | |
| 464 | #d-13 |
| 465 | @result{} |
| 466 | -13 |
| 467 | |
| 468 | #x-13 |
| 469 | @result{} |
| 470 | -19 |
| 471 | |
| 472 | #b+1101 |
| 473 | @result{} |
| 474 | 13 |
| 475 | |
| 476 | #o377 |
| 477 | @result{} |
| 478 | 255 |
| 479 | @end lisp |
| 480 | |
| 481 | The codes for indicating exactness (which can, incidentally, be applied |
| 482 | to all numerical values) are: |
| 483 | |
| 484 | @itemize @bullet |
| 485 | @item |
| 486 | @code{#e}, @code{#E} --- the number is exact |
| 487 | |
| 488 | @item |
| 489 | @code{#i}, @code{#I} --- the number is inexact. |
| 490 | @end itemize |
| 491 | |
| 492 | If the exactness indicator is omitted, the integer is assumed to be exact, |
| 493 | since Guile's internal representation for integers is always exact. |
| 494 | Real numbers have limited precision similar to the precision of the |
| 495 | @code{double} type in C. A consequence of the limited precision is that |
| 496 | all real numbers in Guile are also rational, since any number R with a |
| 497 | limited number of decimal places, say N, can be made into an integer by |
| 498 | multiplying by 10^N. |
| 499 | |
| 500 | |
| 501 | @node Integer Operations |
| 502 | @subsection Operations on Integer Values |
| 503 | @rnindex odd? |
| 504 | @rnindex even? |
| 505 | @rnindex quotient |
| 506 | @rnindex remainder |
| 507 | @rnindex modulo |
| 508 | @rnindex gcd |
| 509 | @rnindex lcm |
| 510 | |
| 511 | @deffn primitive odd? n |
| 512 | Return @code{#t} if @var{n} is an odd number, @code{#f} |
| 513 | otherwise. |
| 514 | @end deffn |
| 515 | |
| 516 | @deffn primitive even? n |
| 517 | Return @code{#t} if @var{n} is an even number, @code{#f} |
| 518 | otherwise. |
| 519 | @end deffn |
| 520 | |
| 521 | @c begin (texi-doc-string "guile" "quotient") |
| 522 | @deffn primitive quotient |
| 523 | Return the quotient of the numbers @var{x} and @var{y}. |
| 524 | @end deffn |
| 525 | |
| 526 | @c begin (texi-doc-string "guile" "remainder") |
| 527 | @deffn primitive remainder |
| 528 | Return the remainder of the numbers @var{x} and @var{y}. |
| 529 | @lisp |
| 530 | (remainder 13 4) @result{} 1 |
| 531 | (remainder -13 4) @result{} -1 |
| 532 | @end lisp |
| 533 | @end deffn |
| 534 | |
| 535 | @c begin (texi-doc-string "guile" "modulo") |
| 536 | @deffn primitive modulo |
| 537 | Return the modulo of the numbers @var{x} and @var{y}. |
| 538 | @lisp |
| 539 | (modulo 13 4) @result{} 1 |
| 540 | (modulo -13 4) @result{} 3 |
| 541 | @end lisp |
| 542 | @end deffn |
| 543 | |
| 544 | @c begin (texi-doc-string "guile" "gcd") |
| 545 | @deffn primitive gcd |
| 546 | Return the greatest common divisor of all arguments. |
| 547 | If called without arguments, 0 is returned. |
| 548 | @end deffn |
| 549 | |
| 550 | @c begin (texi-doc-string "guile" "lcm") |
| 551 | @deffn primitive lcm |
| 552 | Return the least common multiple of the arguments. |
| 553 | If called without arguments, 1 is returned. |
| 554 | @end deffn |
| 555 | |
| 556 | |
| 557 | @node Comparison |
| 558 | @subsection Comparison Predicates |
| 559 | @rnindex zero? |
| 560 | @rnindex positive? |
| 561 | @rnindex negative? |
| 562 | |
| 563 | @c begin (texi-doc-string "guile" "=") |
| 564 | @deffn primitive = |
| 565 | Return @code{#t} if all parameters are numerically equal. |
| 566 | @end deffn |
| 567 | |
| 568 | @c begin (texi-doc-string "guile" "<") |
| 569 | @deffn primitive < |
| 570 | Return @code{#t} if the list of parameters is monotonically |
| 571 | increasing. |
| 572 | @end deffn |
| 573 | |
| 574 | @c begin (texi-doc-string "guile" ">") |
| 575 | @deffn primitive > |
| 576 | Return @code{#t} if the list of parameters is monotonically |
| 577 | decreasing. |
| 578 | @end deffn |
| 579 | |
| 580 | @c begin (texi-doc-string "guile" "<=") |
| 581 | @deffn primitive <= |
| 582 | Return @code{#t} if the list of parameters is monotonically |
| 583 | non-decreasing. |
| 584 | @end deffn |
| 585 | |
| 586 | @c begin (texi-doc-string "guile" ">=") |
| 587 | @deffn primitive >= |
| 588 | Return @code{#t} if the list of parameters is monotonically |
| 589 | non-increasing. |
| 590 | @end deffn |
| 591 | |
| 592 | @c begin (texi-doc-string "guile" "zero?") |
| 593 | @deffn primitive zero? |
| 594 | Return @code{#t} if @var{z} is an exact or inexact number equal to |
| 595 | zero. |
| 596 | @end deffn |
| 597 | |
| 598 | @c begin (texi-doc-string "guile" "positive?") |
| 599 | @deffn primitive positive? |
| 600 | Return @code{#t} if @var{x} is an exact or inexact number greater than |
| 601 | zero. |
| 602 | @end deffn |
| 603 | |
| 604 | @c begin (texi-doc-string "guile" "negative?") |
| 605 | @deffn primitive negative? |
| 606 | Return @code{#t} if @var{x} is an exact or inexact number less than |
| 607 | zero. |
| 608 | @end deffn |
| 609 | |
| 610 | |
| 611 | @node Conversion |
| 612 | @subsection Converting Numbers To and From Strings |
| 613 | @rnindex number->string |
| 614 | @rnindex string->number |
| 615 | |
| 616 | @deffn primitive number->string n [radix] |
| 617 | Return a string holding the external representation of the |
| 618 | number @var{n} in the given @var{radix}. If @var{n} is |
| 619 | inexact, a radix of 10 will be used. |
| 620 | @end deffn |
| 621 | |
| 622 | @deffn primitive string->number string [radix] |
| 623 | Return a number of the maximally precise representation |
| 624 | expressed by the given @var{string}. @var{radix} must be an |
| 625 | exact integer, either 2, 8, 10, or 16. If supplied, @var{radix} |
| 626 | is a default radix that may be overridden by an explicit radix |
| 627 | prefix in @var{string} (e.g. "#o177"). If @var{radix} is not |
| 628 | supplied, then the default radix is 10. If string is not a |
| 629 | syntactically valid notation for a number, then |
| 630 | @code{string->number} returns @code{#f}. |
| 631 | @end deffn |
| 632 | |
| 633 | |
| 634 | @node Complex |
| 635 | @subsection Complex Number Operations |
| 636 | @rnindex make-rectangular |
| 637 | @rnindex make-polar |
| 638 | @rnindex real-part |
| 639 | @rnindex imag-part |
| 640 | @rnindex magnitude |
| 641 | @rnindex angle |
| 642 | |
| 643 | @deffn primitive make-rectangular real imaginary |
| 644 | Return a complex number constructed of the given @var{real} and |
| 645 | @var{imaginary} parts. |
| 646 | @end deffn |
| 647 | |
| 648 | @deffn primitive make-polar x y |
| 649 | Return the complex number @var{x} * e^(i * @var{y}). |
| 650 | @end deffn |
| 651 | |
| 652 | @c begin (texi-doc-string "guile" "real-part") |
| 653 | @deffn primitive real-part |
| 654 | Return the real part of the number @var{z}. |
| 655 | @end deffn |
| 656 | |
| 657 | @c begin (texi-doc-string "guile" "imag-part") |
| 658 | @deffn primitive imag-part |
| 659 | Return the imaginary part of the number @var{z}. |
| 660 | @end deffn |
| 661 | |
| 662 | @c begin (texi-doc-string "guile" "magnitude") |
| 663 | @deffn primitive magnitude |
| 664 | Return the magnitude of the number @var{z}. This is the same as |
| 665 | @code{abs} for real arguments, but also allows complex numbers. |
| 666 | @end deffn |
| 667 | |
| 668 | @c begin (texi-doc-string "guile" "angle") |
| 669 | @deffn primitive angle |
| 670 | Return the angle of the complex number @var{z}. |
| 671 | @end deffn |
| 672 | |
| 673 | |
| 674 | @node Arithmetic |
| 675 | @subsection Arithmetic Functions |
| 676 | @rnindex max |
| 677 | @rnindex min |
| 678 | @rnindex + |
| 679 | @rnindex * |
| 680 | @rnindex - |
| 681 | @rnindex / |
| 682 | @rnindex abs |
| 683 | @rnindex floor |
| 684 | @rnindex ceiling |
| 685 | @rnindex truncate |
| 686 | @rnindex round |
| 687 | |
| 688 | @c begin (texi-doc-string "guile" "+") |
| 689 | @deffn primitive + z1 @dots{} |
| 690 | Return the sum of all parameter values. Return 0 if called without any |
| 691 | parameters. |
| 692 | @end deffn |
| 693 | |
| 694 | @c begin (texi-doc-string "guile" "-") |
| 695 | @deffn primitive - z1 z2 @dots{} |
| 696 | If called with one argument @var{z1}, -@var{z1} is returned. Otherwise |
| 697 | the sum of all but the first argument are subtracted from the first |
| 698 | argument. |
| 699 | @end deffn |
| 700 | |
| 701 | @c begin (texi-doc-string "guile" "*") |
| 702 | @deffn primitive * z1 @dots{} |
| 703 | Return the product of all arguments. If called without arguments, 1 is |
| 704 | returned. |
| 705 | @end deffn |
| 706 | |
| 707 | @c begin (texi-doc-string "guile" "/") |
| 708 | @deffn primitive / z1 z2 @dots{} |
| 709 | Divide the first argument by the product of the remaining arguments. If |
| 710 | called with one argument @var{z1}, 1/@var{z1} is returned. |
| 711 | @end deffn |
| 712 | |
| 713 | @c begin (texi-doc-string "guile" "abs") |
| 714 | @deffn primitive abs x |
| 715 | Return the absolute value of @var{x}. |
| 716 | @end deffn |
| 717 | |
| 718 | @c begin (texi-doc-string "guile" "max") |
| 719 | @deffn primitive max x1 x2 @dots{} |
| 720 | Return the maximum of all parameter values. |
| 721 | @end deffn |
| 722 | |
| 723 | @c begin (texi-doc-string "guile" "min") |
| 724 | @deffn primitive min x1 x2 @dots{} |
| 725 | Return the minium of all parameter values. |
| 726 | @end deffn |
| 727 | |
| 728 | @c begin (texi-doc-string "guile" "truncate") |
| 729 | @deffn primitive truncate |
| 730 | Round the inexact number @var{x} towards zero. |
| 731 | @end deffn |
| 732 | |
| 733 | @c begin (texi-doc-string "guile" "round") |
| 734 | @deffn primitive round x |
| 735 | Round the inexact number @var{x} towards zero. |
| 736 | @end deffn |
| 737 | |
| 738 | @c begin (texi-doc-string "guile" "floor") |
| 739 | @deffn primitive floor x |
| 740 | Round the number @var{x} towards minus infinity. |
| 741 | @end deffn |
| 742 | |
| 743 | @c begin (texi-doc-string "guile" "ceiling") |
| 744 | @deffn primitive ceiling x |
| 745 | Round the number @var{x} towards infinity. |
| 746 | @end deffn |
| 747 | |
| 748 | |
| 749 | @node Scientific |
| 750 | @subsection Scientific Functions |
| 751 | |
| 752 | The following procedures accept any kind of number as arguments, |
| 753 | including complex numbers. |
| 754 | |
| 755 | @rnindex sqrt |
| 756 | @c begin (texi-doc-string "guile" "sqrt") |
| 757 | @deffn procedure sqrt z |
| 758 | Return the square root of @var{z}. |
| 759 | @end deffn |
| 760 | |
| 761 | @rnindex expt |
| 762 | @c begin (texi-doc-string "guile" "expt") |
| 763 | @deffn procedure expt z1 z2 |
| 764 | Return @var{z1} raised to the power of @var{z2}. |
| 765 | @end deffn |
| 766 | |
| 767 | @rnindex sin |
| 768 | @c begin (texi-doc-string "guile" "sin") |
| 769 | @deffn procedure sin z |
| 770 | Return the sine of @var{z}. |
| 771 | @end deffn |
| 772 | |
| 773 | @rnindex cos |
| 774 | @c begin (texi-doc-string "guile" "cos") |
| 775 | @deffn procedure cos z |
| 776 | Return the cosine of @var{z}. |
| 777 | @end deffn |
| 778 | |
| 779 | @rnindex tan |
| 780 | @c begin (texi-doc-string "guile" "tan") |
| 781 | @deffn procedure tan z |
| 782 | Return the tangent of @var{z}. |
| 783 | @end deffn |
| 784 | |
| 785 | @rnindex asin |
| 786 | @c begin (texi-doc-string "guile" "asin") |
| 787 | @deffn procedure asin z |
| 788 | Return the arcsine of @var{z}. |
| 789 | @end deffn |
| 790 | |
| 791 | @rnindex acos |
| 792 | @c begin (texi-doc-string "guile" "acos") |
| 793 | @deffn procedure acos z |
| 794 | Return the arccosine of @var{z}. |
| 795 | @end deffn |
| 796 | |
| 797 | @rnindex atan |
| 798 | @c begin (texi-doc-string "guile" "atan") |
| 799 | @deffn procedure atan z |
| 800 | Return the arctangent of @var{z}. |
| 801 | @end deffn |
| 802 | |
| 803 | @rnindex exp |
| 804 | @c begin (texi-doc-string "guile" "exp") |
| 805 | @deffn procedure exp z |
| 806 | Return e to the power of @var{z}, where e is the base of natural |
| 807 | logarithms (2.71828@dots{}). |
| 808 | @end deffn |
| 809 | |
| 810 | @rnindex log |
| 811 | @c begin (texi-doc-string "guile" "log") |
| 812 | @deffn procedure log z |
| 813 | Return the natural logarithm of @var{z}. |
| 814 | @end deffn |
| 815 | |
| 816 | @c begin (texi-doc-string "guile" "log10") |
| 817 | @deffn procedure log10 z |
| 818 | Return the base 10 logarithm of @var{z}. |
| 819 | @end deffn |
| 820 | |
| 821 | @c begin (texi-doc-string "guile" "sinh") |
| 822 | @deffn procedure sinh z |
| 823 | Return the hyperbolic sine of @var{z}. |
| 824 | @end deffn |
| 825 | |
| 826 | @c begin (texi-doc-string "guile" "cosh") |
| 827 | @deffn procedure cosh z |
| 828 | Return the hyperbolic cosine of @var{z}. |
| 829 | @end deffn |
| 830 | |
| 831 | @c begin (texi-doc-string "guile" "tanh") |
| 832 | @deffn procedure tanh z |
| 833 | Return the hyperbolic tangent of @var{z}. |
| 834 | @end deffn |
| 835 | |
| 836 | @c begin (texi-doc-string "guile" "asinh") |
| 837 | @deffn procedure asinh z |
| 838 | Return the hyperbolic arcsine of @var{z}. |
| 839 | @end deffn |
| 840 | |
| 841 | @c begin (texi-doc-string "guile" "acosh") |
| 842 | @deffn procedure acosh z |
| 843 | Return the hyperbolic arccosine of @var{z}. |
| 844 | @end deffn |
| 845 | |
| 846 | @c begin (texi-doc-string "guile" "atanh") |
| 847 | @deffn procedure atanh z |
| 848 | Return the hyperbolic arctangent of @var{z}. |
| 849 | @end deffn |
| 850 | |
| 851 | |
| 852 | @node Primitive Numerics |
| 853 | @subsection Primitive Numeric Functions |
| 854 | |
| 855 | Many of Guile's numeric procedures which accept any kind of numbers as |
| 856 | arguments, including complex numbers, are implemented as Scheme |
| 857 | procedures that use the following real number-based primitives. These |
| 858 | primitives signal an error if they are called with complex arguments. |
| 859 | |
| 860 | @c begin (texi-doc-string "guile" "$abs") |
| 861 | @deffn primitive $abs x |
| 862 | Return the absolute value of @var{x}. |
| 863 | @end deffn |
| 864 | |
| 865 | @c begin (texi-doc-string "guile" "$sqrt") |
| 866 | @deffn primitive $sqrt x |
| 867 | Return the square root of @var{x}. |
| 868 | @end deffn |
| 869 | |
| 870 | @deffn primitive $expt x y |
| 871 | Return @var{x} raised to the power of @var{y}. This |
| 872 | procedure does not accept complex arguments. |
| 873 | @end deffn |
| 874 | |
| 875 | @c begin (texi-doc-string "guile" "$sin") |
| 876 | @deffn primitive $sin x |
| 877 | Return the sine of @var{x}. |
| 878 | @end deffn |
| 879 | |
| 880 | @c begin (texi-doc-string "guile" "$cos") |
| 881 | @deffn primitive $cos x |
| 882 | Return the cosine of @var{x}. |
| 883 | @end deffn |
| 884 | |
| 885 | @c begin (texi-doc-string "guile" "$tan") |
| 886 | @deffn primitive $tan x |
| 887 | Return the tangent of @var{x}. |
| 888 | @end deffn |
| 889 | |
| 890 | @c begin (texi-doc-string "guile" "$asin") |
| 891 | @deffn primitive $asin x |
| 892 | Return the arcsine of @var{x}. |
| 893 | @end deffn |
| 894 | |
| 895 | @c begin (texi-doc-string "guile" "$acos") |
| 896 | @deffn primitive $acos x |
| 897 | Return the arccosine of @var{x}. |
| 898 | @end deffn |
| 899 | |
| 900 | @c begin (texi-doc-string "guile" "$atan") |
| 901 | @deffn primitive $atan x |
| 902 | Return the arctangent of @var{x} in the range -PI/2 to PI/2. |
| 903 | @end deffn |
| 904 | |
| 905 | @deffn primitive $atan2 x y |
| 906 | Return the arc tangent of the two arguments @var{x} and |
| 907 | @var{y}. This is similar to calculating the arc tangent of |
| 908 | @var{x} / @var{y}, except that the signs of both arguments |
| 909 | are used to determine the quadrant of the result. This |
| 910 | procedure does not accept complex arguments. |
| 911 | @end deffn |
| 912 | |
| 913 | @c begin (texi-doc-string "guile" "$exp") |
| 914 | @deffn primitive $exp x |
| 915 | Return e to the power of @var{x}, where e is the base of natural |
| 916 | logarithms (2.71828@dots{}). |
| 917 | @end deffn |
| 918 | |
| 919 | @c begin (texi-doc-string "guile" "$log") |
| 920 | @deffn primitive $log x |
| 921 | Return the natural logarithm of @var{x}. |
| 922 | @end deffn |
| 923 | |
| 924 | @c begin (texi-doc-string "guile" "$sinh") |
| 925 | @deffn primitive $sinh x |
| 926 | Return the hyperbolic sine of @var{x}. |
| 927 | @end deffn |
| 928 | |
| 929 | @c begin (texi-doc-string "guile" "$cosh") |
| 930 | @deffn primitive $cosh x |
| 931 | Return the hyperbolic cosine of @var{x}. |
| 932 | @end deffn |
| 933 | |
| 934 | @c begin (texi-doc-string "guile" "$tanh") |
| 935 | @deffn primitive $tanh x |
| 936 | Return the hyperbolic tangent of @var{x}. |
| 937 | @end deffn |
| 938 | |
| 939 | @c begin (texi-doc-string "guile" "$asinh") |
| 940 | @deffn primitive $asinh x |
| 941 | Return the hyperbolic arcsine of @var{x}. |
| 942 | @end deffn |
| 943 | |
| 944 | @c begin (texi-doc-string "guile" "$acosh") |
| 945 | @deffn primitive $acosh x |
| 946 | Return the hyperbolic arccosine of @var{x}. |
| 947 | @end deffn |
| 948 | |
| 949 | @c begin (texi-doc-string "guile" "$atanh") |
| 950 | @deffn primitive $atanh x |
| 951 | Return the hyperbolic arctangent of @var{x}. |
| 952 | @end deffn |
| 953 | |
| 954 | |
| 955 | @node Bitwise Operations |
| 956 | @subsection Bitwise Operations |
| 957 | |
| 958 | @deffn primitive logand n1 n2 |
| 959 | Return the integer which is the bit-wise AND of the two integer |
| 960 | arguments. |
| 961 | |
| 962 | @lisp |
| 963 | (number->string (logand #b1100 #b1010) 2) |
| 964 | @result{} "1000" |
| 965 | @end lisp |
| 966 | @end deffn |
| 967 | |
| 968 | @deffn primitive logior n1 n2 |
| 969 | Return the integer which is the bit-wise OR of the two integer |
| 970 | arguments. |
| 971 | |
| 972 | @lisp |
| 973 | (number->string (logior #b1100 #b1010) 2) |
| 974 | @result{} "1110" |
| 975 | @end lisp |
| 976 | @end deffn |
| 977 | |
| 978 | @deffn primitive logxor n1 n2 |
| 979 | Return the integer which is the bit-wise XOR of the two integer |
| 980 | arguments. |
| 981 | |
| 982 | @lisp |
| 983 | (number->string (logxor #b1100 #b1010) 2) |
| 984 | @result{} "110" |
| 985 | @end lisp |
| 986 | @end deffn |
| 987 | |
| 988 | @deffn primitive lognot n |
| 989 | Return the integer which is the 2s-complement of the integer |
| 990 | argument. |
| 991 | |
| 992 | @lisp |
| 993 | (number->string (lognot #b10000000) 2) |
| 994 | @result{} "-10000001" |
| 995 | (number->string (lognot #b0) 2) |
| 996 | @result{} "-1" |
| 997 | @end lisp |
| 998 | @end deffn |
| 999 | |
| 1000 | @deffn primitive logtest j k |
| 1001 | @lisp |
| 1002 | (logtest j k) @equiv{} (not (zero? (logand j k))) |
| 1003 | |
| 1004 | (logtest #b0100 #b1011) @result{} #f |
| 1005 | (logtest #b0100 #b0111) @result{} #t |
| 1006 | @end lisp |
| 1007 | @end deffn |
| 1008 | |
| 1009 | @deffn primitive logbit? index j |
| 1010 | @lisp |
| 1011 | (logbit? index j) @equiv{} (logtest (integer-expt 2 index) j) |
| 1012 | |
| 1013 | (logbit? 0 #b1101) @result{} #t |
| 1014 | (logbit? 1 #b1101) @result{} #f |
| 1015 | (logbit? 2 #b1101) @result{} #t |
| 1016 | (logbit? 3 #b1101) @result{} #t |
| 1017 | (logbit? 4 #b1101) @result{} #f |
| 1018 | @end lisp |
| 1019 | @end deffn |
| 1020 | |
| 1021 | @deffn primitive ash n cnt |
| 1022 | The function ash performs an arithmetic shift left by @var{cnt} |
| 1023 | bits (or shift right, if @var{cnt} is negative). 'Arithmetic' |
| 1024 | means, that the function does not guarantee to keep the bit |
| 1025 | structure of @var{n}, but rather guarantees that the result |
| 1026 | will always be rounded towards minus infinity. Therefore, the |
| 1027 | results of ash and a corresponding bitwise shift will differ if |
| 1028 | @var{n} is negative. |
| 1029 | |
| 1030 | Formally, the function returns an integer equivalent to |
| 1031 | @code{(inexact->exact (floor (* @var{n} (expt 2 @var{cnt}))))}. |
| 1032 | |
| 1033 | @lisp |
| 1034 | (number->string (ash #b1 3) 2) @result{} "1000" |
| 1035 | (number->string (ash #b1010 -1) 2) @result{} "101" |
| 1036 | @end lisp |
| 1037 | @end deffn |
| 1038 | |
| 1039 | @deffn primitive logcount n |
| 1040 | Return the number of bits in integer @var{n}. If integer is |
| 1041 | positive, the 1-bits in its binary representation are counted. |
| 1042 | If negative, the 0-bits in its two's-complement binary |
| 1043 | representation are counted. If 0, 0 is returned. |
| 1044 | |
| 1045 | @lisp |
| 1046 | (logcount #b10101010) |
| 1047 | @result{} 4 |
| 1048 | (logcount 0) |
| 1049 | @result{} 0 |
| 1050 | (logcount -2) |
| 1051 | @result{} 1 |
| 1052 | @end lisp |
| 1053 | @end deffn |
| 1054 | |
| 1055 | @deffn primitive integer-length n |
| 1056 | Return the number of bits neccessary to represent @var{n}. |
| 1057 | |
| 1058 | @lisp |
| 1059 | (integer-length #b10101010) |
| 1060 | @result{} 8 |
| 1061 | (integer-length 0) |
| 1062 | @result{} 0 |
| 1063 | (integer-length #b1111) |
| 1064 | @result{} 4 |
| 1065 | @end lisp |
| 1066 | @end deffn |
| 1067 | |
| 1068 | @deffn primitive integer-expt n k |
| 1069 | Return @var{n} raised to the non-negative integer exponent |
| 1070 | @var{k}. |
| 1071 | |
| 1072 | @lisp |
| 1073 | (integer-expt 2 5) |
| 1074 | @result{} 32 |
| 1075 | (integer-expt -3 3) |
| 1076 | @result{} -27 |
| 1077 | @end lisp |
| 1078 | @end deffn |
| 1079 | |
| 1080 | @deffn primitive bit-extract n start end |
| 1081 | Return the integer composed of the @var{start} (inclusive) |
| 1082 | through @var{end} (exclusive) bits of @var{n}. The |
| 1083 | @var{start}th bit becomes the 0-th bit in the result. |
| 1084 | |
| 1085 | @lisp |
| 1086 | (number->string (bit-extract #b1101101010 0 4) 2) |
| 1087 | @result{} "1010" |
| 1088 | (number->string (bit-extract #b1101101010 4 9) 2) |
| 1089 | @result{} "10110" |
| 1090 | @end lisp |
| 1091 | @end deffn |
| 1092 | |
| 1093 | |
| 1094 | @node Random |
| 1095 | @subsection Random Number Generation |
| 1096 | |
| 1097 | @deffn primitive copy-random-state [state] |
| 1098 | Return a copy of the random state @var{state}. |
| 1099 | @end deffn |
| 1100 | |
| 1101 | @deffn primitive random n [state] |
| 1102 | Return a number in [0,N). |
| 1103 | |
| 1104 | Accepts a positive integer or real n and returns a |
| 1105 | number of the same type between zero (inclusive) and |
| 1106 | N (exclusive). The values returned have a uniform |
| 1107 | distribution. |
| 1108 | |
| 1109 | The optional argument @var{state} must be of the type produced |
| 1110 | by @code{seed->random-state}. It defaults to the value of the |
| 1111 | variable @var{*random-state*}. This object is used to maintain |
| 1112 | the state of the pseudo-random-number generator and is altered |
| 1113 | as a side effect of the random operation. |
| 1114 | @end deffn |
| 1115 | |
| 1116 | @deffn primitive random:exp [state] |
| 1117 | Return an inexact real in an exponential distribution with mean |
| 1118 | 1. For an exponential distribution with mean u use (* u |
| 1119 | (random:exp)). |
| 1120 | @end deffn |
| 1121 | |
| 1122 | @deffn primitive random:hollow-sphere! v [state] |
| 1123 | Fills vect with inexact real random numbers |
| 1124 | the sum of whose squares is equal to 1.0. |
| 1125 | Thinking of vect as coordinates in space of |
| 1126 | dimension n = (vector-length vect), the coordinates |
| 1127 | are uniformly distributed over the surface of the |
| 1128 | unit n-shere. |
| 1129 | @end deffn |
| 1130 | |
| 1131 | @deffn primitive random:normal [state] |
| 1132 | Return an inexact real in a normal distribution. The |
| 1133 | distribution used has mean 0 and standard deviation 1. For a |
| 1134 | normal distribution with mean m and standard deviation d use |
| 1135 | @code{(+ m (* d (random:normal)))}. |
| 1136 | @end deffn |
| 1137 | |
| 1138 | @deffn primitive random:normal-vector! v [state] |
| 1139 | Fills vect with inexact real random numbers that are |
| 1140 | independent and standard normally distributed |
| 1141 | (i.e., with mean 0 and variance 1). |
| 1142 | @end deffn |
| 1143 | |
| 1144 | @deffn primitive random:solid-sphere! v [state] |
| 1145 | Fills vect with inexact real random numbers |
| 1146 | the sum of whose squares is less than 1.0. |
| 1147 | Thinking of vect as coordinates in space of |
| 1148 | dimension n = (vector-length vect), the coordinates |
| 1149 | are uniformly distributed within the unit n-shere. |
| 1150 | The sum of the squares of the numbers is returned. |
| 1151 | @end deffn |
| 1152 | |
| 1153 | @deffn primitive random:uniform [state] |
| 1154 | Return a uniformly distributed inexact real random number in |
| 1155 | [0,1). |
| 1156 | @end deffn |
| 1157 | |
| 1158 | @deffn primitive seed->random-state seed |
| 1159 | Return a new random state using @var{seed}. |
| 1160 | @end deffn |
| 1161 | |
| 1162 | |
| 1163 | @node Characters |
| 1164 | @section Characters |
| 1165 | @tpindex Characters |
| 1166 | |
| 1167 | Most of the characters in the ASCII character set may be referred to by |
| 1168 | name: for example, @code{#\tab}, @code{#\esc}, @code{#\stx}, and so on. |
| 1169 | The following table describes the ASCII names for each character. |
| 1170 | |
| 1171 | @multitable @columnfractions .25 .25 .25 .25 |
| 1172 | @item 0 = @code{#\nul} |
| 1173 | @tab 1 = @code{#\soh} |
| 1174 | @tab 2 = @code{#\stx} |
| 1175 | @tab 3 = @code{#\etx} |
| 1176 | @item 4 = @code{#\eot} |
| 1177 | @tab 5 = @code{#\enq} |
| 1178 | @tab 6 = @code{#\ack} |
| 1179 | @tab 7 = @code{#\bel} |
| 1180 | @item 8 = @code{#\bs} |
| 1181 | @tab 9 = @code{#\ht} |
| 1182 | @tab 10 = @code{#\nl} |
| 1183 | @tab 11 = @code{#\vt} |
| 1184 | @item 12 = @code{#\np} |
| 1185 | @tab 13 = @code{#\cr} |
| 1186 | @tab 14 = @code{#\so} |
| 1187 | @tab 15 = @code{#\si} |
| 1188 | @item 16 = @code{#\dle} |
| 1189 | @tab 17 = @code{#\dc1} |
| 1190 | @tab 18 = @code{#\dc2} |
| 1191 | @tab 19 = @code{#\dc3} |
| 1192 | @item 20 = @code{#\dc4} |
| 1193 | @tab 21 = @code{#\nak} |
| 1194 | @tab 22 = @code{#\syn} |
| 1195 | @tab 23 = @code{#\etb} |
| 1196 | @item 24 = @code{#\can} |
| 1197 | @tab 25 = @code{#\em} |
| 1198 | @tab 26 = @code{#\sub} |
| 1199 | @tab 27 = @code{#\esc} |
| 1200 | @item 28 = @code{#\fs} |
| 1201 | @tab 29 = @code{#\gs} |
| 1202 | @tab 30 = @code{#\rs} |
| 1203 | @tab 31 = @code{#\us} |
| 1204 | @item 32 = @code{#\sp} |
| 1205 | @end multitable |
| 1206 | |
| 1207 | The @code{delete} character (octal 177) may be referred to with the name |
| 1208 | @code{#\del}. |
| 1209 | |
| 1210 | Several characters have more than one name: |
| 1211 | |
| 1212 | @itemize @bullet |
| 1213 | @item |
| 1214 | @code{#\space}, @code{#\sp} |
| 1215 | @item |
| 1216 | @code{#\newline}, @code{#\nl} |
| 1217 | @item |
| 1218 | @code{#\tab}, @code{#\ht} |
| 1219 | @item |
| 1220 | @code{#\backspace}, @code{#\bs} |
| 1221 | @item |
| 1222 | @code{#\return}, @code{#\cr} |
| 1223 | @item |
| 1224 | @code{#\page}, @code{#\np} |
| 1225 | @item |
| 1226 | @code{#\null}, @code{#\nul} |
| 1227 | @end itemize |
| 1228 | |
| 1229 | @rnindex char? |
| 1230 | @deffn primitive char? x |
| 1231 | Return @code{#t} iff @var{x} is a character, else @code{#f}. |
| 1232 | @end deffn |
| 1233 | |
| 1234 | @rnindex char=? |
| 1235 | @deffn primitive char=? x y |
| 1236 | Return @code{#t} iff @var{x} is the same character as @var{y}, else @code{#f}. |
| 1237 | @end deffn |
| 1238 | |
| 1239 | @rnindex char<? |
| 1240 | @deffn primitive char<? x y |
| 1241 | Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence, |
| 1242 | else @code{#f}. |
| 1243 | @end deffn |
| 1244 | |
| 1245 | @rnindex char<=? |
| 1246 | @deffn primitive char<=? x y |
| 1247 | Return @code{#t} iff @var{x} is less than or equal to @var{y} in the |
| 1248 | ASCII sequence, else @code{#f}. |
| 1249 | @end deffn |
| 1250 | |
| 1251 | @rnindex char>? |
| 1252 | @deffn primitive char>? x y |
| 1253 | Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII |
| 1254 | sequence, else @code{#f}. |
| 1255 | @end deffn |
| 1256 | |
| 1257 | @rnindex char>=? |
| 1258 | @deffn primitive char>=? x y |
| 1259 | Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the |
| 1260 | ASCII sequence, else @code{#f}. |
| 1261 | @end deffn |
| 1262 | |
| 1263 | @rnindex char-ci=? |
| 1264 | @deffn primitive char-ci=? x y |
| 1265 | Return @code{#t} iff @var{x} is the same character as @var{y} ignoring |
| 1266 | case, else @code{#f}. |
| 1267 | @end deffn |
| 1268 | |
| 1269 | @rnindex char-ci<? |
| 1270 | @deffn primitive char-ci<? x y |
| 1271 | Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence |
| 1272 | ignoring case, else @code{#f}. |
| 1273 | @end deffn |
| 1274 | |
| 1275 | @rnindex char-ci<=? |
| 1276 | @deffn primitive char-ci<=? x y |
| 1277 | Return @code{#t} iff @var{x} is less than or equal to @var{y} in the |
| 1278 | ASCII sequence ignoring case, else @code{#f}. |
| 1279 | @end deffn |
| 1280 | |
| 1281 | @rnindex char-ci>? |
| 1282 | @deffn primitive char-ci>? x y |
| 1283 | Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII |
| 1284 | sequence ignoring case, else @code{#f}. |
| 1285 | @end deffn |
| 1286 | |
| 1287 | @rnindex char-ci>=? |
| 1288 | @deffn primitive char-ci>=? x y |
| 1289 | Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the |
| 1290 | ASCII sequence ignoring case, else @code{#f}. |
| 1291 | @end deffn |
| 1292 | |
| 1293 | @rnindex char-alphabetic? |
| 1294 | @deffn primitive char-alphabetic? chr |
| 1295 | Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}. |
| 1296 | Alphabetic means the same thing as the isalpha C library function. |
| 1297 | @end deffn |
| 1298 | |
| 1299 | @rnindex char-numeric? |
| 1300 | @deffn primitive char-numeric? chr |
| 1301 | Return @code{#t} iff @var{chr} is numeric, else @code{#f}. |
| 1302 | Numeric means the same thing as the isdigit C library function. |
| 1303 | @end deffn |
| 1304 | |
| 1305 | @rnindex char-whitespace? |
| 1306 | @deffn primitive char-whitespace? chr |
| 1307 | Return @code{#t} iff @var{chr} is whitespace, else @code{#f}. |
| 1308 | Whitespace means the same thing as the isspace C library function. |
| 1309 | @end deffn |
| 1310 | |
| 1311 | @rnindex char-upper-case? |
| 1312 | @deffn primitive char-upper-case? chr |
| 1313 | Return @code{#t} iff @var{chr} is uppercase, else @code{#f}. |
| 1314 | Uppercase means the same thing as the isupper C library function. |
| 1315 | @end deffn |
| 1316 | |
| 1317 | @rnindex char-lower-case? |
| 1318 | @deffn primitive char-lower-case? chr |
| 1319 | Return @code{#t} iff @var{chr} is lowercase, else @code{#f}. |
| 1320 | Lowercase means the same thing as the islower C library function. |
| 1321 | @end deffn |
| 1322 | |
| 1323 | @deffn primitive char-is-both? chr |
| 1324 | Return @code{#t} iff @var{chr} is either uppercase or lowercase, else @code{#f}. |
| 1325 | Uppercase and lowercase are as defined by the isupper and islower |
| 1326 | C library functions. |
| 1327 | @end deffn |
| 1328 | |
| 1329 | @rnindex char->integer |
| 1330 | @deffn primitive char->integer chr |
| 1331 | Return the number corresponding to ordinal position of @var{chr} in the |
| 1332 | ASCII sequence. |
| 1333 | @end deffn |
| 1334 | |
| 1335 | @rnindex integer->char |
| 1336 | @deffn primitive integer->char n |
| 1337 | Return the character at position @var{n} in the ASCII sequence. |
| 1338 | @end deffn |
| 1339 | |
| 1340 | @rnindex char-upcase |
| 1341 | @deffn primitive char-upcase chr |
| 1342 | Return the uppercase character version of @var{chr}. |
| 1343 | @end deffn |
| 1344 | |
| 1345 | @rnindex char-downcase |
| 1346 | @deffn primitive char-downcase chr |
| 1347 | Return the lowercase character version of @var{chr}. |
| 1348 | @end deffn |
| 1349 | |
| 1350 | |
| 1351 | @node Strings |
| 1352 | @section Strings |
| 1353 | @tpindex Strings |
| 1354 | |
| 1355 | Strings are fixed-length sequences of characters. They can be created |
| 1356 | by calling constructor procedures, but they can also literally get |
| 1357 | entered at the REPL or in Scheme source files. |
| 1358 | |
| 1359 | Guile provides a rich set of string processing procedures, because text |
| 1360 | handling is very important when Guile is used as a scripting language. |
| 1361 | |
| 1362 | Strings always carry the information about how many characters they are |
| 1363 | composed of with them, so there is no special end-of-string character, |
| 1364 | like in C. That means that Scheme strings can contain any character, |
| 1365 | even the NUL character @code{'\0'}. But note: Since most operating |
| 1366 | system calls dealing with strings (such as for file operations) expect |
| 1367 | strings to be zero-terminated, they might do unexpected things when |
| 1368 | called with string containing unusal characters. |
| 1369 | |
| 1370 | @menu |
| 1371 | * String Syntax:: Read syntax for strings. |
| 1372 | * String Predicates:: Testing strings for certain properties. |
| 1373 | * String Constructors:: Creating new string objects. |
| 1374 | * List/String Conversion:: Converting from/to lists of characters. |
| 1375 | * String Selection:: Select portions from strings. |
| 1376 | * String Modification:: Modify parts or whole strings. |
| 1377 | * String Comparison:: Lexicographic ordering predicates. |
| 1378 | * String Searching:: Searching in strings. |
| 1379 | * Alphabetic Case Mapping:: Convert the alphabetic case of strings. |
| 1380 | * Appending Strings:: Appending strings to form a new string. |
| 1381 | * String Miscellanea:: Miscellaneous string procedures. |
| 1382 | @end menu |
| 1383 | |
| 1384 | @node String Syntax |
| 1385 | @subsection String Read Syntax |
| 1386 | |
| 1387 | The read syntax for strings is an arbitrarily long sequence of |
| 1388 | characters enclosed in double quotes (@code{"}). @footnote{Actually, the |
| 1389 | current implementation restricts strings to a length of 2^24 |
| 1390 | characters.} If you want to insert a double quote character into a |
| 1391 | string literal, it must be prefixed with a backslash @code{\} character |
| 1392 | (called an @emph{escape character}). |
| 1393 | |
| 1394 | The following are examples of string literals: |
| 1395 | |
| 1396 | @lisp |
| 1397 | "foo" |
| 1398 | "bar plonk" |
| 1399 | "Hello World" |
| 1400 | "\"Hi\", he said." |
| 1401 | @end lisp |
| 1402 | |
| 1403 | @c FIXME::martin: What about escape sequences like \r, \n etc.? |
| 1404 | |
| 1405 | @node String Predicates |
| 1406 | @subsection String Predicates |
| 1407 | |
| 1408 | The following procedures can be used to check whether a given string |
| 1409 | fulfills some specified property. |
| 1410 | |
| 1411 | @rnindex string? |
| 1412 | @deffn primitive string? obj |
| 1413 | Return @code{#t} iff @var{obj} is a string, else returns |
| 1414 | @code{#f}. |
| 1415 | @end deffn |
| 1416 | |
| 1417 | @deffn primitive string-null? str |
| 1418 | Return @code{#t} if @var{str}'s length is nonzero, and |
| 1419 | @code{#f} otherwise. |
| 1420 | @lisp |
| 1421 | (string-null? "") @result{} #t |
| 1422 | y @result{} "foo" |
| 1423 | (string-null? y) @result{} #f |
| 1424 | @end lisp |
| 1425 | @end deffn |
| 1426 | |
| 1427 | @node String Constructors |
| 1428 | @subsection String Constructors |
| 1429 | |
| 1430 | The string constructor procedures create new string objects, possibly |
| 1431 | initializing them with some specified character data. |
| 1432 | |
| 1433 | @c FIXME::martin: list->string belongs into `List/String Conversion' |
| 1434 | |
| 1435 | @rnindex string |
| 1436 | @rnindex list->string |
| 1437 | @deffn primitive string . chrs |
| 1438 | @deffnx primitive list->string chrs |
| 1439 | Return a newly allocated string composed of the arguments, |
| 1440 | @var{chrs}. |
| 1441 | @end deffn |
| 1442 | |
| 1443 | @rnindex make-string |
| 1444 | @deffn primitive make-string k [chr] |
| 1445 | Return a newly allocated string of |
| 1446 | length @var{k}. If @var{chr} is given, then all elements of |
| 1447 | the string are initialized to @var{chr}, otherwise the contents |
| 1448 | of the @var{string} are unspecified. |
| 1449 | @end deffn |
| 1450 | |
| 1451 | @node List/String Conversion |
| 1452 | @subsection List/String conversion |
| 1453 | |
| 1454 | When processing strings, it is often convenient to first convert them |
| 1455 | into a list representation by using the procedure @code{string->list}, |
| 1456 | work with the resulting list, and then convert it back into a string. |
| 1457 | These procedures are useful for similar tasks. |
| 1458 | |
| 1459 | @rnindex string->list |
| 1460 | @deffn primitive string->list str |
| 1461 | Return a newly allocated list of the characters that make up |
| 1462 | the given string @var{str}. @code{string->list} and |
| 1463 | @code{list->string} are inverses as far as @samp{equal?} is |
| 1464 | concerned. |
| 1465 | @end deffn |
| 1466 | |
| 1467 | @deffn primitive string-split str chr |
| 1468 | Split the string @var{str} into the a list of the substrings delimited |
| 1469 | by appearances of the character @var{chr}. Note that an empty substring |
| 1470 | between separator characters will result in an empty string in the |
| 1471 | result list. |
| 1472 | @lisp |
| 1473 | (string-split "root:x:0:0:root:/root:/bin/bash" #\:) |
| 1474 | @result{} |
| 1475 | ("root" "x" "0" "0" "root" "/root" "/bin/bash") |
| 1476 | |
| 1477 | (string-split "::" #\:) |
| 1478 | @result{} |
| 1479 | ("" "" "") |
| 1480 | |
| 1481 | (string-split "" #\:) |
| 1482 | @result{} |
| 1483 | ("") |
| 1484 | @end lisp |
| 1485 | @end deffn |
| 1486 | |
| 1487 | |
| 1488 | @node String Selection |
| 1489 | @subsection String Selection |
| 1490 | |
| 1491 | Portions of strings can be extracted by these procedures. |
| 1492 | @code{string-ref} delivers individual characters whereas |
| 1493 | @code{substring} can be used to extract substrings from longer strings. |
| 1494 | |
| 1495 | @rnindex string-length |
| 1496 | @deffn primitive string-length string |
| 1497 | Return the number of characters in @var{string}. |
| 1498 | @end deffn |
| 1499 | |
| 1500 | @rnindex string-ref |
| 1501 | @deffn primitive string-ref str k |
| 1502 | Return character @var{k} of @var{str} using zero-origin |
| 1503 | indexing. @var{k} must be a valid index of @var{str}. |
| 1504 | @end deffn |
| 1505 | |
| 1506 | @rnindex string-copy |
| 1507 | @deffn primitive string-copy str |
| 1508 | Return a newly allocated copy of the given @var{string}. |
| 1509 | @end deffn |
| 1510 | |
| 1511 | @rnindex substring |
| 1512 | @deffn primitive substring str start [end] |
| 1513 | Return a newly allocated string formed from the characters |
| 1514 | of @var{str} beginning with index @var{start} (inclusive) and |
| 1515 | ending with index @var{end} (exclusive). |
| 1516 | @var{str} must be a string, @var{start} and @var{end} must be |
| 1517 | exact integers satisfying: |
| 1518 | |
| 1519 | 0 <= @var{start} <= @var{end} <= (string-length @var{str}). |
| 1520 | @end deffn |
| 1521 | |
| 1522 | @node String Modification |
| 1523 | @subsection String Modification |
| 1524 | |
| 1525 | These procedures are for modifying strings in-place. That means, that |
| 1526 | not a new string is the result of a string operation, but that the |
| 1527 | actual memory representation of a string is modified. |
| 1528 | |
| 1529 | @rnindex string-set! |
| 1530 | @deffn primitive string-set! str k chr |
| 1531 | Store @var{chr} in element @var{k} of @var{str} and return |
| 1532 | an unspecified value. @var{k} must be a valid index of |
| 1533 | @var{str}. |
| 1534 | @end deffn |
| 1535 | |
| 1536 | @rnindex string-fill! |
| 1537 | @deffn primitive string-fill! str chr |
| 1538 | Store @var{char} in every element of the given @var{string} and |
| 1539 | return an unspecified value. |
| 1540 | @end deffn |
| 1541 | |
| 1542 | @deffn primitive substring-fill! str start end fill |
| 1543 | Change every character in @var{str} between @var{start} and |
| 1544 | @var{end} to @var{fill}. |
| 1545 | |
| 1546 | @lisp |
| 1547 | (define y "abcdefg") |
| 1548 | (substring-fill! y 1 3 #\r) |
| 1549 | y |
| 1550 | @result{} "arrdefg" |
| 1551 | @end lisp |
| 1552 | @end deffn |
| 1553 | |
| 1554 | @deffn primitive substring-move! str1 start1 end1 str2 start2 |
| 1555 | @deffnx primitive substring-move-left! str1 start1 end1 str2 start2 |
| 1556 | @deffnx primitive substring-move-right! str1 start1 end1 str2 start2 |
| 1557 | Copy the substring of @var{str1} bounded by @var{start1} and @var{end1} |
| 1558 | into @var{str2} beginning at position @var{end2}. |
| 1559 | @code{substring-move-right!} begins copying from the rightmost character |
| 1560 | and moves left, and @code{substring-move-left!} copies from the leftmost |
| 1561 | character moving right. |
| 1562 | |
| 1563 | It is useful to have two functions that copy in different directions so |
| 1564 | that substrings can be copied back and forth within a single string. If |
| 1565 | you wish to copy text from the left-hand side of a string to the |
| 1566 | right-hand side of the same string, and the source and destination |
| 1567 | overlap, you must be careful to copy the rightmost characters of the |
| 1568 | text first, to avoid clobbering your data. Hence, when @var{str1} and |
| 1569 | @var{str2} are the same string, you should use |
| 1570 | @code{substring-move-right!} when moving text from left to right, and |
| 1571 | @code{substring-move-left!} otherwise. If @code{str1} and @samp{str2} |
| 1572 | are different strings, it does not matter which function you use. |
| 1573 | |
| 1574 | @example |
| 1575 | (define x (make-string 10 #\a)) |
| 1576 | (define y "bcd") |
| 1577 | (substring-move-left! x 2 5 y 0) |
| 1578 | y |
| 1579 | @result{} "aaa" |
| 1580 | |
| 1581 | x |
| 1582 | @result{} "aaaaaaaaaa" |
| 1583 | |
| 1584 | (define y "bcdefg") |
| 1585 | (substring-move-left! x 2 5 y 0) |
| 1586 | y |
| 1587 | @result{} "aaaefg" |
| 1588 | |
| 1589 | (define y "abcdefg") |
| 1590 | (substring-move-left! y 2 5 y 3) |
| 1591 | y |
| 1592 | @result{} "abccccg" |
| 1593 | |
| 1594 | (define y "abcdefg") |
| 1595 | (substring-move-right! y 2 5 y 0) |
| 1596 | y |
| 1597 | @result{} "ededefg" |
| 1598 | |
| 1599 | (define y "abcdefg") |
| 1600 | (substring-move-right! y 2 5 y 3) |
| 1601 | y |
| 1602 | @result{} "abccdeg" |
| 1603 | @end example |
| 1604 | @end deffn |
| 1605 | |
| 1606 | |
| 1607 | @node String Comparison |
| 1608 | @subsection String Comparison |
| 1609 | |
| 1610 | The procedures in this section are similar to the character ordering |
| 1611 | predicates (@pxref{Characters}), but are defined on character sequences. |
| 1612 | They all return @code{#t} on success and @code{#f} on failure. The |
| 1613 | predicates ending in @code{-ci} ignore the character case when comparing |
| 1614 | strings. |
| 1615 | |
| 1616 | |
| 1617 | @rnindex string=? |
| 1618 | @deffn primitive string=? s1 s2 |
| 1619 | Lexicographic equality predicate; return @code{#t} if the two |
| 1620 | strings are the same length and contain the same characters in |
| 1621 | the same positions, otherwise return @code{#f}. |
| 1622 | |
| 1623 | The procedure @code{string-ci=?} treats upper and lower case |
| 1624 | letters as though they were the same character, but |
| 1625 | @code{string=?} treats upper and lower case as distinct |
| 1626 | characters. |
| 1627 | @end deffn |
| 1628 | |
| 1629 | @rnindex string<? |
| 1630 | @deffn primitive string<? s1 s2 |
| 1631 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
| 1632 | is lexicographically less than @var{s2}. |
| 1633 | @end deffn |
| 1634 | |
| 1635 | @rnindex string<=? |
| 1636 | @deffn primitive string<=? s1 s2 |
| 1637 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
| 1638 | is lexicographically less than or equal to @var{s2}. |
| 1639 | @end deffn |
| 1640 | |
| 1641 | @rnindex string>? |
| 1642 | @deffn primitive string>? s1 s2 |
| 1643 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
| 1644 | is lexicographically greater than @var{s2}. |
| 1645 | @end deffn |
| 1646 | |
| 1647 | @rnindex string>=? |
| 1648 | @deffn primitive string>=? s1 s2 |
| 1649 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
| 1650 | is lexicographically greater than or equal to @var{s2}. |
| 1651 | @end deffn |
| 1652 | |
| 1653 | @rnindex string-ci=? |
| 1654 | @deffn primitive string-ci=? s1 s2 |
| 1655 | Case-insensitive string equality predicate; return @code{#t} if |
| 1656 | the two strings are the same length and their component |
| 1657 | characters match (ignoring case) at each position; otherwise |
| 1658 | return @code{#f}. |
| 1659 | @end deffn |
| 1660 | |
| 1661 | @rnindex string-ci< |
| 1662 | @deffn primitive string-ci<? s1 s2 |
| 1663 | Case insensitive lexicographic ordering predicate; return |
| 1664 | @code{#t} if @var{s1} is lexicographically less than @var{s2} |
| 1665 | regardless of case. |
| 1666 | @end deffn |
| 1667 | |
| 1668 | @rnindex string<=? |
| 1669 | @deffn primitive string-ci<=? s1 s2 |
| 1670 | Case insensitive lexicographic ordering predicate; return |
| 1671 | @code{#t} if @var{s1} is lexicographically less than or equal |
| 1672 | to @var{s2} regardless of case. |
| 1673 | @end deffn |
| 1674 | |
| 1675 | @rnindex string-ci>? |
| 1676 | @deffn primitive string-ci>? s1 s2 |
| 1677 | Case insensitive lexicographic ordering predicate; return |
| 1678 | @code{#t} if @var{s1} is lexicographically greater than |
| 1679 | @var{s2} regardless of case. |
| 1680 | @end deffn |
| 1681 | |
| 1682 | @rnindex string-ci>=? |
| 1683 | @deffn primitive string-ci>=? s1 s2 |
| 1684 | Case insensitive lexicographic ordering predicate; return |
| 1685 | @code{#t} if @var{s1} is lexicographically greater than or |
| 1686 | equal to @var{s2} regardless of case. |
| 1687 | @end deffn |
| 1688 | |
| 1689 | |
| 1690 | @node String Searching |
| 1691 | @subsection String Searching |
| 1692 | |
| 1693 | When searching the index of a character in a string, these procedures |
| 1694 | can be used. |
| 1695 | |
| 1696 | @deffn primitive string-index str chr [frm [to]] |
| 1697 | Return the index of the first occurrence of @var{chr} in |
| 1698 | @var{str}. The optional integer arguments @var{frm} and |
| 1699 | @var{to} limit the search to a portion of the string. This |
| 1700 | procedure essentially implements the @code{index} or |
| 1701 | @code{strchr} functions from the C library. |
| 1702 | |
| 1703 | @lisp |
| 1704 | (string-index "weiner" #\e) |
| 1705 | @result{} 1 |
| 1706 | |
| 1707 | (string-index "weiner" #\e 2) |
| 1708 | @result{} 4 |
| 1709 | |
| 1710 | (string-index "weiner" #\e 2 4) |
| 1711 | @result{} #f |
| 1712 | @end lisp |
| 1713 | @end deffn |
| 1714 | |
| 1715 | @deffn primitive string-rindex str chr [frm [to]] |
| 1716 | Like @code{string-index}, but search from the right of the |
| 1717 | string rather than from the left. This procedure essentially |
| 1718 | implements the @code{rindex} or @code{strrchr} functions from |
| 1719 | the C library. |
| 1720 | |
| 1721 | @lisp |
| 1722 | (string-rindex "weiner" #\e) |
| 1723 | @result{} 4 |
| 1724 | |
| 1725 | (string-rindex "weiner" #\e 2 4) |
| 1726 | @result{} #f |
| 1727 | |
| 1728 | (string-rindex "weiner" #\e 2 5) |
| 1729 | @result{} 4 |
| 1730 | @end lisp |
| 1731 | @end deffn |
| 1732 | |
| 1733 | @node Alphabetic Case Mapping |
| 1734 | @subsection Alphabetic Case Mapping |
| 1735 | |
| 1736 | These are procedures for mapping strings to their upper- or lower-case |
| 1737 | equivalents, respectively, or for capitalizing strings. |
| 1738 | |
| 1739 | @deffn primitive string-upcase str |
| 1740 | Return a freshly allocated string containing the characters of |
| 1741 | @var{str} in upper case. |
| 1742 | @end deffn |
| 1743 | |
| 1744 | @deffn primitive string-upcase! str |
| 1745 | Destructively upcase every character in @var{str} and return |
| 1746 | @var{str}. |
| 1747 | @lisp |
| 1748 | y @result{} "arrdefg" |
| 1749 | (string-upcase! y) @result{} "ARRDEFG" |
| 1750 | y @result{} "ARRDEFG" |
| 1751 | @end lisp |
| 1752 | @end deffn |
| 1753 | |
| 1754 | @deffn primitive string-downcase str |
| 1755 | Return a freshly allocation string containing the characters in |
| 1756 | @var{str} in lower case. |
| 1757 | @end deffn |
| 1758 | |
| 1759 | @deffn primitive string-downcase! str |
| 1760 | Destructively downcase every character in @var{str} and return |
| 1761 | @var{str}. |
| 1762 | @lisp |
| 1763 | y @result{} "ARRDEFG" |
| 1764 | (string-downcase! y) @result{} "arrdefg" |
| 1765 | y @result{} "arrdefg" |
| 1766 | @end lisp |
| 1767 | @end deffn |
| 1768 | |
| 1769 | @deffn primitive string-capitalize str |
| 1770 | Return a freshly allocated string with the characters in |
| 1771 | @var{str}, where the first character of every word is |
| 1772 | capitalized. |
| 1773 | @end deffn |
| 1774 | |
| 1775 | @deffn primitive string-capitalize! str |
| 1776 | Upcase the first character of every word in @var{str} |
| 1777 | destructively and return @var{str}. |
| 1778 | |
| 1779 | @lisp |
| 1780 | y @result{} "hello world" |
| 1781 | (string-capitalize! y) @result{} "Hello World" |
| 1782 | y @result{} "Hello World" |
| 1783 | @end lisp |
| 1784 | @end deffn |
| 1785 | |
| 1786 | |
| 1787 | @node Appending Strings |
| 1788 | @subsection Appending Strings |
| 1789 | |
| 1790 | The procedure @code{string-append} appends several strings together to |
| 1791 | form a longer result string. |
| 1792 | |
| 1793 | @rnindex string-append |
| 1794 | @deffn primitive string-append string1 @dots{} |
| 1795 | Return a newly allocated string whose characters form the |
| 1796 | concatenation of the given strings. |
| 1797 | @end deffn |
| 1798 | |
| 1799 | |
| 1800 | @node String Miscellanea |
| 1801 | @subsection String Miscellanea |
| 1802 | |
| 1803 | This section contains all remaining string procedures. |
| 1804 | |
| 1805 | @deffn primitive string-ci->symbol str |
| 1806 | Return the symbol whose name is @var{str}. @var{str} is |
| 1807 | converted to lowercase before the conversion is done, if Guile |
| 1808 | is currently reading symbols case-insensitively. |
| 1809 | @end deffn |
| 1810 | |
| 1811 | |
| 1812 | @node Regular Expressions |
| 1813 | @section Regular Expressions |
| 1814 | @tpindex Regular expressions |
| 1815 | |
| 1816 | @cindex regular expressions |
| 1817 | @cindex regex |
| 1818 | @cindex emacs regexp |
| 1819 | |
| 1820 | A @dfn{regular expression} (or @dfn{regexp}) is a pattern that |
| 1821 | describes a whole class of strings. A full description of regular |
| 1822 | expressions and their syntax is beyond the scope of this manual; |
| 1823 | an introduction can be found in the Emacs manual (@pxref{Regexps, |
| 1824 | , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}, or |
| 1825 | in many general Unix reference books. |
| 1826 | |
| 1827 | If your system does not include a POSIX regular expression library, and |
| 1828 | you have not linked Guile with a third-party regexp library such as Rx, |
| 1829 | these functions will not be available. You can tell whether your Guile |
| 1830 | installation includes regular expression support by checking whether the |
| 1831 | @code{*features*} list includes the @code{regex} symbol. |
| 1832 | |
| 1833 | @menu |
| 1834 | * Regexp Functions:: Functions that create and match regexps. |
| 1835 | * Match Structures:: Finding what was matched by a regexp. |
| 1836 | * Backslash Escapes:: Removing the special meaning of regexp metacharacters. |
| 1837 | * Rx Interface:: Tom Lord's Rx library does things differently. |
| 1838 | @end menu |
| 1839 | |
| 1840 | [FIXME: it may be useful to include an Examples section. Parts of this |
| 1841 | interface are bewildering on first glance.] |
| 1842 | |
| 1843 | @node Regexp Functions |
| 1844 | @subsection Regexp Functions |
| 1845 | |
| 1846 | By default, Guile supports POSIX extended regular expressions. |
| 1847 | That means that the characters @samp{(}, @samp{)}, @samp{+} and |
| 1848 | @samp{?} are special, and must be escaped if you wish to match the |
| 1849 | literal characters. |
| 1850 | |
| 1851 | This regular expression interface was modeled after that |
| 1852 | implemented by SCSH, the Scheme Shell. It is intended to be |
| 1853 | upwardly compatible with SCSH regular expressions. |
| 1854 | |
| 1855 | @c begin (scm-doc-string "regex.scm" "string-match") |
| 1856 | @deffn procedure string-match pattern str [start] |
| 1857 | Compile the string @var{pattern} into a regular expression and compare |
| 1858 | it with @var{str}. The optional numeric argument @var{start} specifies |
| 1859 | the position of @var{str} at which to begin matching. |
| 1860 | |
| 1861 | @code{string-match} returns a @dfn{match structure} which |
| 1862 | describes what, if anything, was matched by the regular |
| 1863 | expression. @xref{Match Structures}. If @var{str} does not match |
| 1864 | @var{pattern} at all, @code{string-match} returns @code{#f}. |
| 1865 | @end deffn |
| 1866 | |
| 1867 | Each time @code{string-match} is called, it must compile its |
| 1868 | @var{pattern} argument into a regular expression structure. This |
| 1869 | operation is expensive, which makes @code{string-match} inefficient if |
| 1870 | the same regular expression is used several times (for example, in a |
| 1871 | loop). For better performance, you can compile a regular expression in |
| 1872 | advance and then match strings against the compiled regexp. |
| 1873 | |
| 1874 | @deffn primitive make-regexp pat . flags |
| 1875 | Compile the regular expression described by @var{pat}, and |
| 1876 | return the compiled regexp structure. If @var{pat} does not |
| 1877 | describe a legal regular expression, @code{make-regexp} throws |
| 1878 | a @code{regular-expression-syntax} error. |
| 1879 | |
| 1880 | The @var{flags} arguments change the behavior of the compiled |
| 1881 | regular expression. The following flags may be supplied: |
| 1882 | |
| 1883 | @table @code |
| 1884 | @item regexp/icase |
| 1885 | Consider uppercase and lowercase letters to be the same when |
| 1886 | matching. |
| 1887 | @item regexp/newline |
| 1888 | If a newline appears in the target string, then permit the |
| 1889 | @samp{^} and @samp{$} operators to match immediately after or |
| 1890 | immediately before the newline, respectively. Also, the |
| 1891 | @samp{.} and @samp{[^...]} operators will never match a newline |
| 1892 | character. The intent of this flag is to treat the target |
| 1893 | string as a buffer containing many lines of text, and the |
| 1894 | regular expression as a pattern that may match a single one of |
| 1895 | those lines. |
| 1896 | @item regexp/basic |
| 1897 | Compile a basic (``obsolete'') regexp instead of the extended |
| 1898 | (``modern'') regexps that are the default. Basic regexps do |
| 1899 | not consider @samp{|}, @samp{+} or @samp{?} to be special |
| 1900 | characters, and require the @samp{@{...@}} and @samp{(...)} |
| 1901 | metacharacters to be backslash-escaped (@pxref{Backslash |
| 1902 | Escapes}). There are several other differences between basic |
| 1903 | and extended regular expressions, but these are the most |
| 1904 | significant. |
| 1905 | @item regexp/extended |
| 1906 | Compile an extended regular expression rather than a basic |
| 1907 | regexp. This is the default behavior; this flag will not |
| 1908 | usually be needed. If a call to @code{make-regexp} includes |
| 1909 | both @code{regexp/basic} and @code{regexp/extended} flags, the |
| 1910 | one which comes last will override the earlier one. |
| 1911 | @end table |
| 1912 | @end deffn |
| 1913 | |
| 1914 | @deffn primitive regexp-exec rx str [start [flags]] |
| 1915 | Match the compiled regular expression @var{rx} against |
| 1916 | @code{str}. If the optional integer @var{start} argument is |
| 1917 | provided, begin matching from that position in the string. |
| 1918 | Return a match structure describing the results of the match, |
| 1919 | or @code{#f} if no match could be found. |
| 1920 | @end deffn |
| 1921 | |
| 1922 | @deffn primitive regexp? obj |
| 1923 | Return @code{#t} if @var{obj} is a compiled regular expression, |
| 1924 | or @code{#f} otherwise. |
| 1925 | @end deffn |
| 1926 | |
| 1927 | Regular expressions are commonly used to find patterns in one string and |
| 1928 | replace them with the contents of another string. |
| 1929 | |
| 1930 | @c begin (scm-doc-string "regex.scm" "regexp-substitute") |
| 1931 | @deffn procedure regexp-substitute port match [item@dots{}] |
| 1932 | Write to the output port @var{port} selected contents of the match |
| 1933 | structure @var{match}. Each @var{item} specifies what should be |
| 1934 | written, and may be one of the following arguments: |
| 1935 | |
| 1936 | @itemize @bullet |
| 1937 | @item |
| 1938 | A string. String arguments are written out verbatim. |
| 1939 | |
| 1940 | @item |
| 1941 | An integer. The submatch with that number is written. |
| 1942 | |
| 1943 | @item |
| 1944 | The symbol @samp{pre}. The portion of the matched string preceding |
| 1945 | the regexp match is written. |
| 1946 | |
| 1947 | @item |
| 1948 | The symbol @samp{post}. The portion of the matched string following |
| 1949 | the regexp match is written. |
| 1950 | @end itemize |
| 1951 | |
| 1952 | @var{port} may be @code{#f}, in which case nothing is written; instead, |
| 1953 | @code{regexp-substitute} constructs a string from the specified |
| 1954 | @var{item}s and returns that. |
| 1955 | @end deffn |
| 1956 | |
| 1957 | @c begin (scm-doc-string "regex.scm" "regexp-substitute") |
| 1958 | @deffn procedure regexp-substitute/global port regexp target [item@dots{}] |
| 1959 | Similar to @code{regexp-substitute}, but can be used to perform global |
| 1960 | substitutions on @var{str}. Instead of taking a match structure as an |
| 1961 | argument, @code{regexp-substitute/global} takes two string arguments: a |
| 1962 | @var{regexp} string describing a regular expression, and a @var{target} |
| 1963 | string which should be matched against this regular expression. |
| 1964 | |
| 1965 | Each @var{item} behaves as in @var{regexp-substitute}, with the |
| 1966 | following exceptions: |
| 1967 | |
| 1968 | @itemize @bullet |
| 1969 | @item |
| 1970 | A function may be supplied. When this function is called, it will be |
| 1971 | passed one argument: a match structure for a given regular expression |
| 1972 | match. It should return a string to be written out to @var{port}. |
| 1973 | |
| 1974 | @item |
| 1975 | The @samp{post} symbol causes @code{regexp-substitute/global} to recurse |
| 1976 | on the unmatched portion of @var{str}. This @emph{must} be supplied in |
| 1977 | order to perform global search-and-replace on @var{str}; if it is not |
| 1978 | present among the @var{item}s, then @code{regexp-substitute/global} will |
| 1979 | return after processing a single match. |
| 1980 | @end itemize |
| 1981 | @end deffn |
| 1982 | |
| 1983 | @node Match Structures |
| 1984 | @subsection Match Structures |
| 1985 | |
| 1986 | @cindex match structures |
| 1987 | |
| 1988 | A @dfn{match structure} is the object returned by @code{string-match} and |
| 1989 | @code{regexp-exec}. It describes which portion of a string, if any, |
| 1990 | matched the given regular expression. Match structures include: a |
| 1991 | reference to the string that was checked for matches; the starting and |
| 1992 | ending positions of the regexp match; and, if the regexp included any |
| 1993 | parenthesized subexpressions, the starting and ending positions of each |
| 1994 | submatch. |
| 1995 | |
| 1996 | In each of the regexp match functions described below, the @code{match} |
| 1997 | argument must be a match structure returned by a previous call to |
| 1998 | @code{string-match} or @code{regexp-exec}. Most of these functions |
| 1999 | return some information about the original target string that was |
| 2000 | matched against a regular expression; we will call that string |
| 2001 | @var{target} for easy reference. |
| 2002 | |
| 2003 | @c begin (scm-doc-string "regex.scm" "regexp-match?") |
| 2004 | @deffn procedure regexp-match? obj |
| 2005 | Return @code{#t} if @var{obj} is a match structure returned by a |
| 2006 | previous call to @code{regexp-exec}, or @code{#f} otherwise. |
| 2007 | @end deffn |
| 2008 | |
| 2009 | @c begin (scm-doc-string "regex.scm" "match:substring") |
| 2010 | @deffn procedure match:substring match [n] |
| 2011 | Return the portion of @var{target} matched by subexpression number |
| 2012 | @var{n}. Submatch 0 (the default) represents the entire regexp match. |
| 2013 | If the regular expression as a whole matched, but the subexpression |
| 2014 | number @var{n} did not match, return @code{#f}. |
| 2015 | @end deffn |
| 2016 | |
| 2017 | @c begin (scm-doc-string "regex.scm" "match:start") |
| 2018 | @deffn procedure match:start match [n] |
| 2019 | Return the starting position of submatch number @var{n}. |
| 2020 | @end deffn |
| 2021 | |
| 2022 | @c begin (scm-doc-string "regex.scm" "match:end") |
| 2023 | @deffn procedure match:end match [n] |
| 2024 | Return the ending position of submatch number @var{n}. |
| 2025 | @end deffn |
| 2026 | |
| 2027 | @c begin (scm-doc-string "regex.scm" "match:prefix") |
| 2028 | @deffn procedure match:prefix match |
| 2029 | Return the unmatched portion of @var{target} preceding the regexp match. |
| 2030 | @end deffn |
| 2031 | |
| 2032 | @c begin (scm-doc-string "regex.scm" "match:suffix") |
| 2033 | @deffn procedure match:suffix match |
| 2034 | Return the unmatched portion of @var{target} following the regexp match. |
| 2035 | @end deffn |
| 2036 | |
| 2037 | @c begin (scm-doc-string "regex.scm" "match:count") |
| 2038 | @deffn procedure match:count match |
| 2039 | Return the number of parenthesized subexpressions from @var{match}. |
| 2040 | Note that the entire regular expression match itself counts as a |
| 2041 | subexpression, and failed submatches are included in the count. |
| 2042 | @end deffn |
| 2043 | |
| 2044 | @c begin (scm-doc-string "regex.scm" "match:string") |
| 2045 | @deffn procedure match:string match |
| 2046 | Return the original @var{target} string. |
| 2047 | @end deffn |
| 2048 | |
| 2049 | @node Backslash Escapes |
| 2050 | @subsection Backslash Escapes |
| 2051 | |
| 2052 | Sometimes you will want a regexp to match characters like @samp{*} or |
| 2053 | @samp{$} exactly. For example, to check whether a particular string |
| 2054 | represents a menu entry from an Info node, it would be useful to match |
| 2055 | it against a regexp like @samp{^* [^:]*::}. However, this won't work; |
| 2056 | because the asterisk is a metacharacter, it won't match the @samp{*} at |
| 2057 | the beginning of the string. In this case, we want to make the first |
| 2058 | asterisk un-magic. |
| 2059 | |
| 2060 | You can do this by preceding the metacharacter with a backslash |
| 2061 | character @samp{\}. (This is also called @dfn{quoting} the |
| 2062 | metacharacter, and is known as a @dfn{backslash escape}.) When Guile |
| 2063 | sees a backslash in a regular expression, it considers the following |
| 2064 | glyph to be an ordinary character, no matter what special meaning it |
| 2065 | would ordinarily have. Therefore, we can make the above example work by |
| 2066 | changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells |
| 2067 | the regular expression engine to match only a single asterisk in the |
| 2068 | target string. |
| 2069 | |
| 2070 | Since the backslash is itself a metacharacter, you may force a regexp to |
| 2071 | match a backslash in the target string by preceding the backslash with |
| 2072 | itself. For example, to find variable references in a @TeX{} program, |
| 2073 | you might want to find occurrences of the string @samp{\let\} followed |
| 2074 | by any number of alphabetic characters. The regular expression |
| 2075 | @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the |
| 2076 | regexp each match a single backslash in the target string. |
| 2077 | |
| 2078 | @c begin (scm-doc-string "regex.scm" "regexp-quote") |
| 2079 | @deffn procedure regexp-quote str |
| 2080 | Quote each special character found in @var{str} with a backslash, and |
| 2081 | return the resulting string. |
| 2082 | @end deffn |
| 2083 | |
| 2084 | @strong{Very important:} Using backslash escapes in Guile source code |
| 2085 | (as in Emacs Lisp or C) can be tricky, because the backslash character |
| 2086 | has special meaning for the Guile reader. For example, if Guile |
| 2087 | encounters the character sequence @samp{\n} in the middle of a string |
| 2088 | while processing Scheme code, it replaces those characters with a |
| 2089 | newline character. Similarly, the character sequence @samp{\t} is |
| 2090 | replaced by a horizontal tab. Several of these @dfn{escape sequences} |
| 2091 | are processed by the Guile reader before your code is executed. |
| 2092 | Unrecognized escape sequences are ignored: if the characters @samp{\*} |
| 2093 | appear in a string, they will be translated to the single character |
| 2094 | @samp{*}. |
| 2095 | |
| 2096 | This translation is obviously undesirable for regular expressions, since |
| 2097 | we want to be able to include backslashes in a string in order to |
| 2098 | escape regexp metacharacters. Therefore, to make sure that a backslash |
| 2099 | is preserved in a string in your Guile program, you must use @emph{two} |
| 2100 | consecutive backslashes: |
| 2101 | |
| 2102 | @lisp |
| 2103 | (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*")) |
| 2104 | @end lisp |
| 2105 | |
| 2106 | The string in this example is preprocessed by the Guile reader before |
| 2107 | any code is executed. The resulting argument to @code{make-regexp} is |
| 2108 | the string @samp{^\* [^:]*}, which is what we really want. |
| 2109 | |
| 2110 | This also means that in order to write a regular expression that matches |
| 2111 | a single backslash character, the regular expression string in the |
| 2112 | source code must include @emph{four} backslashes. Each consecutive pair |
| 2113 | of backslashes gets translated by the Guile reader to a single |
| 2114 | backslash, and the resulting double-backslash is interpreted by the |
| 2115 | regexp engine as matching a single backslash character. Hence: |
| 2116 | |
| 2117 | @lisp |
| 2118 | (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*")) |
| 2119 | @end lisp |
| 2120 | |
| 2121 | The reason for the unwieldiness of this syntax is historical. Both |
| 2122 | regular expression pattern matchers and Unix string processing systems |
| 2123 | have traditionally used backslashes with the special meanings |
| 2124 | described above. The POSIX regular expression specification and ANSI C |
| 2125 | standard both require these semantics. Attempting to abandon either |
| 2126 | convention would cause other kinds of compatibility problems, possibly |
| 2127 | more severe ones. Therefore, without extending the Scheme reader to |
| 2128 | support strings with different quoting conventions (an ungainly and |
| 2129 | confusing extension when implemented in other languages), we must adhere |
| 2130 | to this cumbersome escape syntax. |
| 2131 | |
| 2132 | @node Rx Interface |
| 2133 | @subsection Rx Interface |
| 2134 | |
| 2135 | @c FIXME::martin: Shouldn't this be removed or moved to the |
| 2136 | @c ``Guile Modules'' chapter? The functions are not available in |
| 2137 | @c plain Guile... |
| 2138 | |
| 2139 | [FIXME: this is taken from Gary and Mark's quick summaries and should be |
| 2140 | reviewed and expanded. Rx is pretty stable, so could already be done!] |
| 2141 | |
| 2142 | @cindex rx |
| 2143 | @cindex finite automaton |
| 2144 | |
| 2145 | Guile includes an interface to Tom Lord's Rx library (currently only to |
| 2146 | POSIX regular expressions). Use of the library requires a two step |
| 2147 | process: compile a regular expression into an efficient structure, then |
| 2148 | use the structure in any number of string comparisons. |
| 2149 | |
| 2150 | For example, given the |
| 2151 | regular expression @samp{abc.} (which matches any string containing |
| 2152 | @samp{abc} followed by any single character): |
| 2153 | |
| 2154 | @smalllisp |
| 2155 | guile> @kbd{(define r (regcomp "abc."))} |
| 2156 | guile> @kbd{r} |
| 2157 | #<rgx abc.> |
| 2158 | guile> @kbd{(regexec r "abc")} |
| 2159 | #f |
| 2160 | guile> @kbd{(regexec r "abcd")} |
| 2161 | #((0 . 4)) |
| 2162 | guile> |
| 2163 | @end smalllisp |
| 2164 | |
| 2165 | The definitions of @code{regcomp} and @code{regexec} are as follows: |
| 2166 | |
| 2167 | @c NJFIXME not in libguile! |
| 2168 | @deffn primitive regcomp pattern [flags] |
| 2169 | Compile the regular expression pattern using POSIX rules. Flags is |
| 2170 | optional and should be specified using symbolic names: |
| 2171 | @defvar REG_EXTENDED |
| 2172 | use extended POSIX syntax |
| 2173 | @end defvar |
| 2174 | @defvar REG_ICASE |
| 2175 | use case-insensitive matching |
| 2176 | @end defvar |
| 2177 | @defvar REG_NEWLINE |
| 2178 | allow anchors to match after newline characters in the |
| 2179 | string and prevents @code{.} or @code{[^...]} from matching newlines. |
| 2180 | @end defvar |
| 2181 | |
| 2182 | The @code{logior} procedure can be used to combine multiple flags. |
| 2183 | The default is to use |
| 2184 | POSIX basic syntax, which makes @code{+} and @code{?} literals and @code{\+} |
| 2185 | and @code{\?} |
| 2186 | operators. Backslashes in @var{pattern} must be escaped if specified in a |
| 2187 | literal string e.g., @code{"\\(a\\)\\?"}. |
| 2188 | @end deffn |
| 2189 | |
| 2190 | @c NJFIXME not in libguile! |
| 2191 | @deffn primitive regexec regex string [match-pick] [flags] |
| 2192 | |
| 2193 | Match @var{string} against the compiled POSIX regular expression |
| 2194 | @var{regex}. |
| 2195 | @var{match-pick} and @var{flags} are optional. Possible flags (which can be |
| 2196 | combined using the logior procedure) are: |
| 2197 | |
| 2198 | @defvar REG_NOTBOL |
| 2199 | The beginning of line operator won't match the beginning of |
| 2200 | @var{string} (presumably because it's not the beginning of a line) |
| 2201 | @end defvar |
| 2202 | |
| 2203 | @defvar REG_NOTEOL |
| 2204 | Similar to REG_NOTBOL, but prevents the end of line operator |
| 2205 | from matching the end of @var{string}. |
| 2206 | @end defvar |
| 2207 | |
| 2208 | If no match is possible, regexec returns #f. Otherwise @var{match-pick} |
| 2209 | determines the return value: |
| 2210 | |
| 2211 | @code{#t} or unspecified: a newly-allocated vector is returned, |
| 2212 | containing pairs with the indices of the matched part of @var{string} and any |
| 2213 | substrings. |
| 2214 | |
| 2215 | @code{""}: a list is returned: the first element contains a nested list |
| 2216 | with the matched part of @var{string} surrounded by the the unmatched parts. |
| 2217 | Remaining elements are matched substrings (if any). All returned |
| 2218 | substrings share memory with @var{string}. |
| 2219 | |
| 2220 | @code{#f}: regexec returns #t if a match is made, otherwise #f. |
| 2221 | |
| 2222 | vector: the supplied vector is returned, with the first element replaced |
| 2223 | by a pair containing the indices of the matched portion of @var{string} and |
| 2224 | further elements replaced by pairs containing the indices of matched |
| 2225 | substrings (if any). |
| 2226 | |
| 2227 | list: a list will be returned, with each member of the list |
| 2228 | specified by a code in the corresponding position of the supplied list: |
| 2229 | |
| 2230 | a number: the numbered matching substring (0 for the entire match). |
| 2231 | |
| 2232 | @code{#\<}: the beginning of @var{string} to the beginning of the part matched |
| 2233 | by regex. |
| 2234 | |
| 2235 | @code{#\>}: the end of the matched part of @var{string} to the end of |
| 2236 | @var{string}. |
| 2237 | |
| 2238 | @code{#\c}: the "final tag", which seems to be associated with the "cut |
| 2239 | operator", which doesn't seem to be available through the posix |
| 2240 | interface. |
| 2241 | |
| 2242 | e.g., @code{(list #\< 0 1 #\>)}. The returned substrings share memory with |
| 2243 | @var{string}. |
| 2244 | @end deffn |
| 2245 | |
| 2246 | Here are some other procedures that might be used when using regular |
| 2247 | expressions: |
| 2248 | |
| 2249 | @c NJFIXME not in libguile! |
| 2250 | @deffn primitive compiled-regexp? obj |
| 2251 | Test whether obj is a compiled regular expression. |
| 2252 | @end deffn |
| 2253 | |
| 2254 | @c NJFIXME not in libguile! |
| 2255 | @deffn primitive regexp->dfa regex [flags] |
| 2256 | @end deffn |
| 2257 | |
| 2258 | @c NJFIXME not in libguile! |
| 2259 | @deffn primitive dfa-fork dfa |
| 2260 | @end deffn |
| 2261 | |
| 2262 | @c NJFIXME not in libguile! |
| 2263 | @deffn primitive reset-dfa! dfa |
| 2264 | @end deffn |
| 2265 | |
| 2266 | @c NJFIXME not in libguile! |
| 2267 | @deffn primitive dfa-final-tag dfa |
| 2268 | @end deffn |
| 2269 | |
| 2270 | @c NJFIXME not in libguile! |
| 2271 | @deffn primitive dfa-continuable? dfa |
| 2272 | @end deffn |
| 2273 | |
| 2274 | @c NJFIXME not in libguile! |
| 2275 | @deffn primitive advance-dfa! dfa string |
| 2276 | @end deffn |
| 2277 | |
| 2278 | |
| 2279 | @node Symbols and Variables |
| 2280 | @section Symbols and Variables |
| 2281 | |
| 2282 | @c FIXME::martin: Review me! |
| 2283 | |
| 2284 | Symbols are a data type with a special property. On the one hand, |
| 2285 | symbols are used for denoting variables in a Scheme program, on the |
| 2286 | other they can be used as literal data as well. |
| 2287 | |
| 2288 | The association between symbols and values is maintained in special data |
| 2289 | structures, the symbol tables. |
| 2290 | |
| 2291 | In addition, Guile offers variables as first-class objects. They can |
| 2292 | be used for interacting with the module system. |
| 2293 | |
| 2294 | @menu |
| 2295 | * Symbols:: All about symbols as a data type. |
| 2296 | * Symbol Tables:: Tables for mapping symbols to values. |
| 2297 | * Variables:: First-class variables. |
| 2298 | @end menu |
| 2299 | |
| 2300 | @node Symbols |
| 2301 | @subsection Symbols |
| 2302 | @tpindex Symbols |
| 2303 | |
| 2304 | @c FIXME::martin: Review me! |
| 2305 | |
| 2306 | Symbols are especially useful because two symbols which are spelled the |
| 2307 | same way are equivalent in the sense of @code{eq?}. That means that |
| 2308 | they are actually the same Scheme object. The advantage is that symbols |
| 2309 | can be compared extremely efficiently, although they carry more |
| 2310 | information for the human reader than, say, numbers. |
| 2311 | |
| 2312 | It is very common in Scheme programs to use symbols as keys in |
| 2313 | association lists (@pxref{Association Lists}) or hash tables |
| 2314 | (@pxref{Hash Tables}), because this usage improves the readability a |
| 2315 | lot, and does not cause any performance loss. |
| 2316 | |
| 2317 | The read syntax for symbols is a sequence of letters, digits, and |
| 2318 | @emph{extended alphabetic characters} that begins with a character that |
| 2319 | cannot begin a number is an identifier. In addition, @code{+}, |
| 2320 | @code{-}, and @code{...} are identifiers. |
| 2321 | |
| 2322 | Extended alphabetic characters may be used within identifiers as if |
| 2323 | they were letters. The following are extended alphabetic characters: |
| 2324 | |
| 2325 | @example |
| 2326 | ! $ % & * + - . / : < = > ? @@ ^ _ ~ |
| 2327 | @end example |
| 2328 | |
| 2329 | In addition to the read syntax defined above (which is taken from R5RS |
| 2330 | (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on Scheme})), Guile |
| 2331 | provides a method for writing symbols with unusual characters, such as |
| 2332 | space characters. If you (for whatever reason) need to write a symbol |
| 2333 | containing characters not mentioned above, you write symbols as follows: |
| 2334 | |
| 2335 | @itemize @bullet |
| 2336 | @item |
| 2337 | Begin the symbol with the two character @code{#@{}, |
| 2338 | |
| 2339 | @item |
| 2340 | write the characters of the symbol and |
| 2341 | |
| 2342 | @item |
| 2343 | finish the symbol with the characters @code{@}#}. |
| 2344 | @end itemize |
| 2345 | |
| 2346 | Here are a few examples of this form of read syntax; the first |
| 2347 | containing a space character, the second containing a line break and the |
| 2348 | last one looks like a number. |
| 2349 | |
| 2350 | @lisp |
| 2351 | #@{foo bar@}# |
| 2352 | #@{what |
| 2353 | ever@}# |
| 2354 | #@{4242@}# |
| 2355 | @end lisp |
| 2356 | |
| 2357 | Usage of this form of read syntax is discouraged, because it is not |
| 2358 | portable at all, and is not very readable. |
| 2359 | |
| 2360 | @rnindex symbol? |
| 2361 | @deffn primitive symbol? obj |
| 2362 | Return @code{#t} if @var{obj} is a symbol, otherwise return |
| 2363 | @code{#f}. |
| 2364 | @end deffn |
| 2365 | |
| 2366 | @rnindex string->symbol |
| 2367 | @deffn primitive string->symbol string |
| 2368 | Return the symbol whose name is @var{string}. This procedure |
| 2369 | can create symbols with names containing special characters or |
| 2370 | letters in the non-standard case, but it is usually a bad idea |
| 2371 | to create such symbols because in some implementations of |
| 2372 | Scheme they cannot be read as themselves. See |
| 2373 | @code{symbol->string}. |
| 2374 | |
| 2375 | The following examples assume that the implementation's |
| 2376 | standard case is lower case: |
| 2377 | |
| 2378 | @lisp |
| 2379 | (eq? 'mISSISSIppi 'mississippi) @result{} #t |
| 2380 | (string->symbol "mISSISSIppi") @result{} @r{the symbol with name "mISSISSIppi"} |
| 2381 | (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f |
| 2382 | (eq? 'JollyWog |
| 2383 | (string->symbol (symbol->string 'JollyWog))) @result{} #t |
| 2384 | (string=? "K. Harper, M.D." |
| 2385 | (symbol->string |
| 2386 | (string->symbol "K. Harper, M.D."))) @result{}#t |
| 2387 | @end lisp |
| 2388 | @end deffn |
| 2389 | |
| 2390 | @rnindex symbol->string |
| 2391 | @deffn primitive symbol->string s |
| 2392 | Return the name of @var{symbol} as a string. If the symbol was |
| 2393 | part of an object returned as the value of a literal expression |
| 2394 | (section @pxref{Literal expressions,,,r5rs, The Revised^5 |
| 2395 | Report on Scheme}) or by a call to the @code{read} procedure, |
| 2396 | and its name contains alphabetic characters, then the string |
| 2397 | returned will contain characters in the implementation's |
| 2398 | preferred standard case--some implementations will prefer |
| 2399 | upper case, others lower case. If the symbol was returned by |
| 2400 | @code{string->symbol}, the case of characters in the string |
| 2401 | returned will be the same as the case in the string that was |
| 2402 | passed to @code{string->symbol}. It is an error to apply |
| 2403 | mutation procedures like @code{string-set!} to strings returned |
| 2404 | by this procedure. |
| 2405 | |
| 2406 | The following examples assume that the implementation's |
| 2407 | standard case is lower case: |
| 2408 | |
| 2409 | @lisp |
| 2410 | (symbol->string 'flying-fish) @result{} "flying-fish" |
| 2411 | (symbol->string 'Martin) @result{} "martin" |
| 2412 | (symbol->string |
| 2413 | (string->symbol "Malvina")) @result{} "Malvina" |
| 2414 | @end lisp |
| 2415 | @end deffn |
| 2416 | |
| 2417 | @node Symbol Tables |
| 2418 | @subsection Symbol Tables |
| 2419 | |
| 2420 | @c FIXME::martin: Review me! |
| 2421 | |
| 2422 | @c FIXME::martin: Are all these procedures still relevant? |
| 2423 | |
| 2424 | Guile symbol tables are hash tables. Each hash table, also called an |
| 2425 | @dfn{obarray} (for `object array'), is a vector of association lists. |
| 2426 | Each entry in the alists is a pair (@var{SYMBOL} . @var{VALUE}). To |
| 2427 | @dfn{intern} a symbol in a symbol table means to return its |
| 2428 | (@var{SYMBOL} . @var{VALUE}) pair, adding a new entry to the symbol |
| 2429 | table (with an undefined value) if none is yet present. |
| 2430 | |
| 2431 | @c FIXME::martin: According to NEWS, removed. Remove here too, or |
| 2432 | @c leave for compatibility? |
| 2433 | @c @c docstring begin (texi-doc-string "guile" "builtin-bindings") |
| 2434 | @c @deffn primitive builtin-bindings |
| 2435 | @c Create and return a copy of the global symbol table, removing all |
| 2436 | @c unbound symbols. |
| 2437 | @c @end deffn |
| 2438 | |
| 2439 | @deffn primitive gensym [prefix] |
| 2440 | Create a new symbol with a name constructed from a prefix and |
| 2441 | a counter value. The string @var{prefix} can be specified as |
| 2442 | an optional argument. Default prefix is @code{g}. The counter |
| 2443 | is increased by 1 at each call. There is no provision for |
| 2444 | resetting the counter. |
| 2445 | @end deffn |
| 2446 | |
| 2447 | @deffn primitive gentemp [prefix [obarray]] |
| 2448 | Create a new symbol with a name unique in an obarray. |
| 2449 | The name is constructed from an optional string @var{prefix} |
| 2450 | and a counter value. The default prefix is @code{t}. The |
| 2451 | @var{obarray} is specified as a second optional argument. |
| 2452 | Default is the system obarray where all normal symbols are |
| 2453 | interned. The counter is increased by 1 at each |
| 2454 | call. There is no provision for resetting the counter. |
| 2455 | @end deffn |
| 2456 | |
| 2457 | @deffn primitive intern-symbol obarray string |
| 2458 | Add a new symbol to @var{obarray} with name @var{string}, bound to an |
| 2459 | unspecified initial value. The symbol table is not modified if a symbol |
| 2460 | with this name is already present. |
| 2461 | @end deffn |
| 2462 | |
| 2463 | @deffn primitive string->obarray-symbol obarray string [soft?] |
| 2464 | Intern a new symbol in @var{obarray}, a symbol table, with name |
| 2465 | @var{string}. |
| 2466 | @end deffn |
| 2467 | |
| 2468 | @deffn primitive symbol-binding obarray string |
| 2469 | Look up in @var{obarray} the symbol whose name is @var{string}, and |
| 2470 | return the value to which it is bound. If @var{obarray} is @code{#f}, |
| 2471 | use the global symbol table. If @var{string} is not interned in |
| 2472 | @var{obarray}, an error is signalled. |
| 2473 | @end deffn |
| 2474 | |
| 2475 | @deffn primitive symbol-bound? obarray string |
| 2476 | Return @code{#t} if @var{obarray} contains a symbol with name |
| 2477 | @var{string} bound to a defined value. This differs from |
| 2478 | @var{symbol-interned?} in that the mere mention of a symbol |
| 2479 | usually causes it to be interned; @code{symbol-bound?} |
| 2480 | determines whether a symbol has been given any meaningful |
| 2481 | value. |
| 2482 | @end deffn |
| 2483 | |
| 2484 | @deffn primitive symbol-fref symbol |
| 2485 | Return the contents of @var{symbol}'s @dfn{function slot}. |
| 2486 | @end deffn |
| 2487 | |
| 2488 | @deffn primitive symbol-fset! symbol value |
| 2489 | Change the binding of @var{symbol}'s function slot. |
| 2490 | @end deffn |
| 2491 | |
| 2492 | @deffn primitive symbol-hash symbol |
| 2493 | Return a hash value for @var{symbol}. |
| 2494 | @end deffn |
| 2495 | |
| 2496 | @deffn primitive symbol-interned? obarray string |
| 2497 | Return @code{#t} if @var{obarray} contains a symbol with name |
| 2498 | @var{string}, and @code{#f} otherwise. |
| 2499 | @end deffn |
| 2500 | |
| 2501 | @deffn primitive symbol-pref symbol |
| 2502 | Return the @dfn{property list} currently associated with @var{symbol}. |
| 2503 | @end deffn |
| 2504 | |
| 2505 | @deffn primitive symbol-pset! symbol value |
| 2506 | Change the binding of @var{symbol}'s property slot. |
| 2507 | @end deffn |
| 2508 | |
| 2509 | @deffn primitive symbol-set! obarray string value |
| 2510 | Find the symbol in @var{obarray} whose name is @var{string}, and rebind |
| 2511 | it to @var{value}. An error is signalled if @var{string} is not present |
| 2512 | in @var{obarray}. |
| 2513 | @end deffn |
| 2514 | |
| 2515 | @deffn primitive unintern-symbol obarray string |
| 2516 | Remove the symbol with name @var{string} from @var{obarray}. This |
| 2517 | function returns @code{#t} if the symbol was present and @code{#f} |
| 2518 | otherwise. |
| 2519 | @end deffn |
| 2520 | |
| 2521 | @node Variables |
| 2522 | @subsection Variables |
| 2523 | @tpindex Variables |
| 2524 | |
| 2525 | @c FIXME::martin: Review me! |
| 2526 | |
| 2527 | Variables are objects with two fields. They contain a value and they |
| 2528 | can contain a symbol, which is the name of the variable. A variable is |
| 2529 | said to be bound if it does not contain the object denoting unbound |
| 2530 | variables in the value slot. |
| 2531 | |
| 2532 | Variables do not have a read syntax, they have to be created by calling |
| 2533 | one of the constructor procedures @code{make-variable} or |
| 2534 | @code{make-undefined-variable} or retrieved by @code{builtin-variable}. |
| 2535 | |
| 2536 | First-class variables are especially useful for interacting with the |
| 2537 | current module system (@pxref{The Guile module system}). |
| 2538 | |
| 2539 | @deffn primitive builtin-variable name |
| 2540 | Return the built-in variable with the name @var{name}. |
| 2541 | @var{name} must be a symbol (not a string). |
| 2542 | Then use @code{variable-ref} to access its value. |
| 2543 | @end deffn |
| 2544 | |
| 2545 | @deffn primitive make-undefined-variable [name-hint] |
| 2546 | Return a variable object initialized to an undefined value. |
| 2547 | If given, uses @var{name-hint} as its internal (debugging) |
| 2548 | name, otherwise just treat it as an anonymous variable. |
| 2549 | Remember, of course, that multiple bindings to the same |
| 2550 | variable may exist, so @var{name-hint} is just that---a hint. |
| 2551 | @end deffn |
| 2552 | |
| 2553 | @deffn primitive make-variable init [name-hint] |
| 2554 | Return a variable object initialized to value @var{init}. |
| 2555 | If given, uses @var{name-hint} as its internal (debugging) |
| 2556 | name, otherwise just treat it as an anonymous variable. |
| 2557 | Remember, of course, that multiple bindings to the same |
| 2558 | variable may exist, so @var{name-hint} is just that---a hint. |
| 2559 | @end deffn |
| 2560 | |
| 2561 | @deffn primitive variable-bound? var |
| 2562 | Return @code{#t} iff @var{var} is bound to a value. |
| 2563 | Throws an error if @var{var} is not a variable object. |
| 2564 | @end deffn |
| 2565 | |
| 2566 | @deffn primitive variable-ref var |
| 2567 | Dereference @var{var} and return its value. |
| 2568 | @var{var} must be a variable object; see @code{make-variable} |
| 2569 | and @code{make-undefined-variable}. |
| 2570 | @end deffn |
| 2571 | |
| 2572 | @deffn primitive variable-set! var val |
| 2573 | Set the value of the variable @var{var} to @var{val}. |
| 2574 | @var{var} must be a variable object, @var{val} can be any |
| 2575 | value. Return an unspecified value. |
| 2576 | @end deffn |
| 2577 | |
| 2578 | @deffn primitive variable? obj |
| 2579 | Return @code{#t} iff @var{obj} is a variable object, else |
| 2580 | return @code{#f} |
| 2581 | @end deffn |
| 2582 | |
| 2583 | |
| 2584 | @node Keywords |
| 2585 | @section Keywords |
| 2586 | @tpindex Keywords |
| 2587 | |
| 2588 | Keywords are self-evaluating objects with a convenient read syntax that |
| 2589 | makes them easy to type. |
| 2590 | |
| 2591 | Guile's keyword support conforms to R5RS, and adds a (switchable) read |
| 2592 | syntax extension to permit keywords to begin with @code{:} as well as |
| 2593 | @code{#:}. |
| 2594 | |
| 2595 | @menu |
| 2596 | * Why Use Keywords?:: Motivation for keyword usage. |
| 2597 | * Coding With Keywords:: How to use keywords. |
| 2598 | * Keyword Read Syntax:: Read syntax for keywords. |
| 2599 | * Keyword Procedures:: Procedures for dealing with keywords. |
| 2600 | * Keyword Primitives:: The underlying primitive procedures. |
| 2601 | @end menu |
| 2602 | |
| 2603 | @node Why Use Keywords? |
| 2604 | @subsection Why Use Keywords? |
| 2605 | |
| 2606 | Keywords are useful in contexts where a program or procedure wants to be |
| 2607 | able to accept a large number of optional arguments without making its |
| 2608 | interface unmanageable. |
| 2609 | |
| 2610 | To illustrate this, consider a hypothetical @code{make-window} |
| 2611 | procedure, which creates a new window on the screen for drawing into |
| 2612 | using some graphical toolkit. There are many parameters that the caller |
| 2613 | might like to specify, but which could also be sensibly defaulted, for |
| 2614 | example: |
| 2615 | |
| 2616 | @itemize @bullet |
| 2617 | @item |
| 2618 | colour depth -- Default: the colour depth for the screen |
| 2619 | |
| 2620 | @item |
| 2621 | background colour -- Default: white |
| 2622 | |
| 2623 | @item |
| 2624 | width -- Default: 600 |
| 2625 | |
| 2626 | @item |
| 2627 | height -- Default: 400 |
| 2628 | @end itemize |
| 2629 | |
| 2630 | If @code{make-window} did not use keywords, the caller would have to |
| 2631 | pass in a value for each possible argument, remembering the correct |
| 2632 | argument order and using a special value to indicate the default value |
| 2633 | for that argument: |
| 2634 | |
| 2635 | @lisp |
| 2636 | (make-window 'default ;; Colour depth |
| 2637 | 'default ;; Background colour |
| 2638 | 800 ;; Width |
| 2639 | 100 ;; Height |
| 2640 | @dots{}) ;; More make-window arguments |
| 2641 | @end lisp |
| 2642 | |
| 2643 | With keywords, on the other hand, defaulted arguments are omitted, and |
| 2644 | non-default arguments are clearly tagged by the appropriate keyword. As |
| 2645 | a result, the invocation becomes much clearer: |
| 2646 | |
| 2647 | @lisp |
| 2648 | (make-window #:width 800 #:height 100) |
| 2649 | @end lisp |
| 2650 | |
| 2651 | On the other hand, for a simpler procedure with few arguments, the use |
| 2652 | of keywords would be a hindrance rather than a help. The primitive |
| 2653 | procedure @code{cons}, for example, would not be improved if it had to |
| 2654 | be invoked as |
| 2655 | |
| 2656 | @lisp |
| 2657 | (cons #:car x #:cdr y) |
| 2658 | @end lisp |
| 2659 | |
| 2660 | So the decision whether to use keywords or not is purely pragmatic: use |
| 2661 | them if they will clarify the procedure invocation at point of call. |
| 2662 | |
| 2663 | @node Coding With Keywords |
| 2664 | @subsection Coding With Keywords |
| 2665 | |
| 2666 | If a procedure wants to support keywords, it should take a rest argument |
| 2667 | and then use whatever means is convenient to extract keywords and their |
| 2668 | corresponding arguments from the contents of that rest argument. |
| 2669 | |
| 2670 | The following example illustrates the principle: the code for |
| 2671 | @code{make-window} uses a helper procedure called |
| 2672 | @code{get-keyword-value} to extract individual keyword arguments from |
| 2673 | the rest argument. |
| 2674 | |
| 2675 | @lisp |
| 2676 | (define (get-keyword-value args keyword default) |
| 2677 | (let ((kv (memq keyword args))) |
| 2678 | (if (and kv (>= (length kv) 2)) |
| 2679 | (cadr kv) |
| 2680 | default))) |
| 2681 | |
| 2682 | (define (make-window . args) |
| 2683 | (let ((depth (get-keyword-value args #:depth screen-depth)) |
| 2684 | (bg (get-keyword-value args #:bg "white")) |
| 2685 | (width (get-keyword-value args #:width 800)) |
| 2686 | (height (get-keyword-value args #:height 100)) |
| 2687 | @dots{}) |
| 2688 | @dots{})) |
| 2689 | @end lisp |
| 2690 | |
| 2691 | But you don't need to write @code{get-keyword-value}. The @code{(ice-9 |
| 2692 | optargs)} module provides a set of powerful macros that you can use to |
| 2693 | implement keyword-supporting procedures like this: |
| 2694 | |
| 2695 | @lisp |
| 2696 | (use-modules (ice-9 optargs)) |
| 2697 | |
| 2698 | (define (make-window . args) |
| 2699 | (let-keywords args #f ((depth screen-depth) |
| 2700 | (bg "white") |
| 2701 | (width 800) |
| 2702 | (height 100)) |
| 2703 | ...)) |
| 2704 | @end lisp |
| 2705 | |
| 2706 | @noindent |
| 2707 | Or, even more economically, like this: |
| 2708 | |
| 2709 | @lisp |
| 2710 | (use-modules (ice-9 optargs)) |
| 2711 | |
| 2712 | (define* (make-window #:key (depth screen-depth) |
| 2713 | (bg "white") |
| 2714 | (width 800) |
| 2715 | (height 100)) |
| 2716 | ...) |
| 2717 | @end lisp |
| 2718 | |
| 2719 | For further details on @code{let-keywords}, @code{define*} and other |
| 2720 | facilities provided by the @code{(ice-9 optargs)} module, @ref{Optional |
| 2721 | Arguments}. |
| 2722 | |
| 2723 | |
| 2724 | @node Keyword Read Syntax |
| 2725 | @subsection Keyword Read Syntax |
| 2726 | |
| 2727 | Guile, by default, only recognizes the keyword syntax specified by R5RS. |
| 2728 | A token of the form @code{#:NAME}, where @code{NAME} has the same syntax |
| 2729 | as a Scheme symbol, is the external representation of the keyword named |
| 2730 | @code{NAME}. Keyword objects print using this syntax as well, so values |
| 2731 | containing keyword objects can be read back into Guile. When used in an |
| 2732 | expression, keywords are self-quoting objects. |
| 2733 | |
| 2734 | If the @code{keyword} read option is set to @code{'prefix}, Guile also |
| 2735 | recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens |
| 2736 | of the form @code{:NAME} are read as symbols, as required by R5RS. |
| 2737 | |
| 2738 | To enable and disable the alternative non-R5RS keyword syntax, you use |
| 2739 | the @code{read-options} procedure documented in @ref{General option |
| 2740 | interface} and @ref{Reader options}. |
| 2741 | |
| 2742 | @smalllisp |
| 2743 | (read-set! keywords 'prefix) |
| 2744 | |
| 2745 | #:type |
| 2746 | @result{} |
| 2747 | #:type |
| 2748 | |
| 2749 | :type |
| 2750 | @result{} |
| 2751 | #:type |
| 2752 | |
| 2753 | (read-set! keywords #f) |
| 2754 | |
| 2755 | #:type |
| 2756 | @result{} |
| 2757 | #:type |
| 2758 | |
| 2759 | :type |
| 2760 | @result{} |
| 2761 | ERROR: In expression :type: |
| 2762 | ERROR: Unbound variable: :type |
| 2763 | ABORT: (unbound-variable) |
| 2764 | @end smalllisp |
| 2765 | |
| 2766 | @node Keyword Procedures |
| 2767 | @subsection Keyword Procedures |
| 2768 | |
| 2769 | @c FIXME::martin: Review me! |
| 2770 | |
| 2771 | The following procedures can be used for converting symbols to keywords |
| 2772 | and back. |
| 2773 | |
| 2774 | @deffn procedure symbol->keyword sym |
| 2775 | Return a keyword with the same characters as in @var{sym}. |
| 2776 | @end deffn |
| 2777 | |
| 2778 | @deffn procedure keyword->symbol kw |
| 2779 | Return a symbol with the same characters as in @var{kw}. |
| 2780 | @end deffn |
| 2781 | |
| 2782 | |
| 2783 | @node Keyword Primitives |
| 2784 | @subsection Keyword Primitives |
| 2785 | |
| 2786 | Internally, a keyword is implemented as something like a tagged symbol, |
| 2787 | where the tag identifies the keyword as being self-evaluating, and the |
| 2788 | symbol, known as the keyword's @dfn{dash symbol} has the same name as |
| 2789 | the keyword name but prefixed by a single dash. For example, the |
| 2790 | keyword @code{#:name} has the corresponding dash symbol @code{-name}. |
| 2791 | |
| 2792 | Most keyword objects are constructed automatically by the reader when it |
| 2793 | reads a token beginning with @code{#:}. However, if you need to |
| 2794 | construct a keyword object programmatically, you can do so by calling |
| 2795 | @code{make-keyword-from-dash-symbol} with the corresponding dash symbol |
| 2796 | (as the reader does). The dash symbol for a keyword object can be |
| 2797 | retrieved using the @code{keyword-dash-symbol} procedure. |
| 2798 | |
| 2799 | @deffn primitive make-keyword-from-dash-symbol symbol |
| 2800 | Make a keyword object from a @var{symbol} that starts with a dash. |
| 2801 | @end deffn |
| 2802 | |
| 2803 | @deffn primitive keyword? obj |
| 2804 | Return @code{#t} if the argument @var{obj} is a keyword, else |
| 2805 | @code{#f}. |
| 2806 | @end deffn |
| 2807 | |
| 2808 | @deffn primitive keyword-dash-symbol keyword |
| 2809 | Return the dash symbol for @var{keyword}. |
| 2810 | This is the inverse of @code{make-keyword-from-dash-symbol}. |
| 2811 | @end deffn |
| 2812 | |
| 2813 | @node Pairs |
| 2814 | @section Pairs |
| 2815 | @tpindex Pairs |
| 2816 | |
| 2817 | @c FIXME::martin: Review me! |
| 2818 | |
| 2819 | Pairs are used to combine two Scheme objects into one compound object. |
| 2820 | Hence the name: A pair stores a pair of objects. |
| 2821 | |
| 2822 | The data type @emph{pair} is extremely important in Scheme, just like in |
| 2823 | any other Lisp dialect. The reason is that pairs are not only used to |
| 2824 | make two values available as one object, but that pairs are used for |
| 2825 | constructing lists of values. Because lists are so important in Scheme, |
| 2826 | they are described in a section of their own (@pxref{Lists}). |
| 2827 | |
| 2828 | Pairs can literally get entered in source code or at the REPL, in the |
| 2829 | so-called @dfn{dotted list} syntax. This syntax consists of an opening |
| 2830 | parentheses, the first element of the pair, a dot, the second element |
| 2831 | and a closing parentheses. The following example shows how a pair |
| 2832 | consisting of the two numbers 1 and 2, and a pair containing the symbols |
| 2833 | @code{foo} and @code{bar} can be entered. It is very important to write |
| 2834 | the whitespace before and after the dot, because otherwise the Scheme |
| 2835 | parser whould not be able to figure out where to split the tokens. |
| 2836 | |
| 2837 | @lisp |
| 2838 | (1 . 2) |
| 2839 | (foo . bar) |
| 2840 | @end lisp |
| 2841 | |
| 2842 | But beware, if you want to try out these examples, you have to |
| 2843 | @dfn{quote} the expressions. More information about quotation is |
| 2844 | available in the section (REFFIXME). The correct way to try these |
| 2845 | examples is as follows. |
| 2846 | |
| 2847 | @lisp |
| 2848 | '(1 . 2) |
| 2849 | @result{} |
| 2850 | (1 . 2) |
| 2851 | '(foo . bar) |
| 2852 | @result{} |
| 2853 | (foo . bar) |
| 2854 | @end lisp |
| 2855 | |
| 2856 | A new pair is made by calling the procedure @code{cons} with two |
| 2857 | arguments. Then the argument values are stored into a newly allocated |
| 2858 | pair, and the pair is returned. The name @code{cons} stands for |
| 2859 | @emph{construct}. Use the procedure @code{pair?} to test whether a |
| 2860 | given Scheme object is a pair or not. |
| 2861 | |
| 2862 | @rnindex cons |
| 2863 | @deffn primitive cons x y |
| 2864 | Return a newly allocated pair whose car is @var{x} and whose |
| 2865 | cdr is @var{y}. The pair is guaranteed to be different (in the |
| 2866 | sense of @code{eq?}) from every previously existing object. |
| 2867 | @end deffn |
| 2868 | |
| 2869 | @rnindex pair? |
| 2870 | @deffn primitive pair? x |
| 2871 | Return @code{#t} if @var{x} is a pair; otherwise return |
| 2872 | @code{#f}. |
| 2873 | @end deffn |
| 2874 | |
| 2875 | The two parts of a pair are traditionally called @emph{car} and |
| 2876 | @emph{cdr}. They can be retrieved with procedures of the same name |
| 2877 | (@code{car} and @code{cdr}), and can be modified with the procedures |
| 2878 | @code{set-car!} and @code{set-cdr!}. Since a very common operation in |
| 2879 | Scheme programs is to access the car of a pair, or the car of the cdr of |
| 2880 | a pair, etc., the procedures called @code{caar}, @code{cadr} and so on |
| 2881 | are also predefined. |
| 2882 | |
| 2883 | @rnindex car |
| 2884 | @rnindex cdr |
| 2885 | @deffn primitive car pair |
| 2886 | @deffnx primitive cdr pair |
| 2887 | Return the car or the cdr of @var{pair}, respectively. |
| 2888 | @end deffn |
| 2889 | |
| 2890 | @deffn primitive caar pair |
| 2891 | @deffnx primitive cadr pair @dots{} |
| 2892 | @deffnx primitive cdddar pair |
| 2893 | @deffnx primitive cddddr pair |
| 2894 | These procedures are compositions of @code{car} and @code{cdr}, where |
| 2895 | for example @code{caddr} could be defined by |
| 2896 | |
| 2897 | @lisp |
| 2898 | (define caddr (lambda (x) (car (cdr (cdr x))))) |
| 2899 | @end lisp |
| 2900 | @end deffn |
| 2901 | |
| 2902 | @rnindex set-car! |
| 2903 | @deffn primitive set-car! pair value |
| 2904 | Stores @var{value} in the car field of @var{pair}. The value returned |
| 2905 | by @code{set-car!} is unspecified. |
| 2906 | @end deffn |
| 2907 | |
| 2908 | @rnindex set-cdr! |
| 2909 | @deffn primitive set-cdr! pair value |
| 2910 | Stores @var{value} in the cdr field of @var{pair}. The value returned |
| 2911 | by @code{set-cdr!} is unspecified. |
| 2912 | @end deffn |
| 2913 | |
| 2914 | |
| 2915 | @node Lists |
| 2916 | @section Lists |
| 2917 | @tpindex Lists |
| 2918 | |
| 2919 | @c FIXME::martin: Review me! |
| 2920 | |
| 2921 | A very important data type in Scheme---as well as in all other Lisp |
| 2922 | dialects---is the data type @dfn{list}.@footnote{Strictly speaking, |
| 2923 | Scheme does not have a real datatype @emph{list}. Lists are made up of |
| 2924 | chained @emph{pairs}, and only exist by definition---a list is a chain |
| 2925 | of pairs which looks like a list.} |
| 2926 | |
| 2927 | This is the short definition of what a list is: |
| 2928 | |
| 2929 | @itemize @bullet |
| 2930 | @item |
| 2931 | Either the empty list @code{()}, |
| 2932 | |
| 2933 | @item |
| 2934 | or a pair which has a list in its cdr. |
| 2935 | @end itemize |
| 2936 | |
| 2937 | @c FIXME::martin: Describe the pair chaining in more detail. |
| 2938 | |
| 2939 | @c FIXME::martin: What is a proper, what an improper list? |
| 2940 | @c What is a circular list? |
| 2941 | |
| 2942 | @c FIXME::martin: Maybe steal some graphics from the Elisp reference |
| 2943 | @c manual? |
| 2944 | |
| 2945 | @menu |
| 2946 | * List Syntax:: Writing literal lists. |
| 2947 | * List Predicates:: Testing lists. |
| 2948 | * List Constructors:: Creating new lists. |
| 2949 | * List Selection:: Selecting from lists, getting their length. |
| 2950 | * Append/Reverse:: Appending and reversing lists. |
| 2951 | * List Modifification:: Modifying list structure. |
| 2952 | * List Searching:: Searching for list elements |
| 2953 | * List Mapping:: Applying procedures to lists. |
| 2954 | @end menu |
| 2955 | |
| 2956 | @node List Syntax |
| 2957 | @subsection List Read Syntax |
| 2958 | |
| 2959 | @c FIXME::martin: Review me! |
| 2960 | |
| 2961 | The syntax for lists is an opening parentheses, then all the elements of |
| 2962 | the list (separated by whitespace) and finally a closing |
| 2963 | parentheses.@footnote{Note that there is no separation character between |
| 2964 | the list elements, like a comma or a semicolon.}. |
| 2965 | |
| 2966 | @lisp |
| 2967 | (1 2 3) ; @r{a list of the numbers 1, 2 and 3} |
| 2968 | ("foo" bar 3.1415) ; @r{a string, a symbol and a real number} |
| 2969 | () ; @r{the empty list} |
| 2970 | @end lisp |
| 2971 | |
| 2972 | The last example needs a bit more explanation. A list with no elements, |
| 2973 | called the @dfn{empty list}, is special in some ways. It is used for |
| 2974 | terminating lists by storing it into the cdr of the last pair that makes |
| 2975 | up a list. An example will clear that up: |
| 2976 | |
| 2977 | @lisp |
| 2978 | (car '(1)) |
| 2979 | @result{} |
| 2980 | 1 |
| 2981 | (cdr '(1)) |
| 2982 | @result{} |
| 2983 | () |
| 2984 | @end lisp |
| 2985 | |
| 2986 | This example also shows that lists have to be quoted (REFFIXME) when |
| 2987 | written, because they would otherwise be mistakingly taken as procedure |
| 2988 | applications (@pxref{Simple Invocation}). |
| 2989 | |
| 2990 | |
| 2991 | @node List Predicates |
| 2992 | @subsection List Predicates |
| 2993 | |
| 2994 | @c FIXME::martin: Review me! |
| 2995 | |
| 2996 | Often it is useful to test whether a given Scheme object is a list or |
| 2997 | not. List-processing procedures could use this information to test |
| 2998 | whether their input is valid, or they could do different things |
| 2999 | depending on the datatype of their arguments. |
| 3000 | |
| 3001 | @rnindex list? |
| 3002 | @deffn primitive list? x |
| 3003 | Return @code{#t} iff @var{x} is a proper list, else @code{#f}. |
| 3004 | @end deffn |
| 3005 | |
| 3006 | The predicate @code{null?} is often used in list-processing code to |
| 3007 | tell whether a given list has run out of elements. That is, a loop |
| 3008 | somehow deals with the elements of a list until the list satisfies |
| 3009 | @code{null?}. Then, teh algorithm terminates. |
| 3010 | |
| 3011 | @rnindex null? |
| 3012 | @deffn primitive null? x |
| 3013 | Return @code{#t} iff @var{x} is the empty list, else @code{#f}. |
| 3014 | @end deffn |
| 3015 | |
| 3016 | @node List Constructors |
| 3017 | @subsection List Constructors |
| 3018 | |
| 3019 | This section describes the procedures for constructing new lists. |
| 3020 | @code{list} simply returns a list where the elements are the arguments, |
| 3021 | @code{cons*} is similar, but the last argument is stored in the cdr of |
| 3022 | the last pair of the list. |
| 3023 | |
| 3024 | @rnindex list |
| 3025 | @deffn primitive list arg1 @dots{} |
| 3026 | Return a list containing @var{objs}, the arguments to |
| 3027 | @code{list}. |
| 3028 | @end deffn |
| 3029 | |
| 3030 | @deffn primitive cons* arg1 arg2 @dots{} |
| 3031 | Like @code{list}, but the last arg provides the tail of the |
| 3032 | constructed list, returning @code{(cons @var{arg1} (cons |
| 3033 | @var{arg2} (cons @dots{} @var{argn})))}. Requires at least one |
| 3034 | argument. If given one argument, that argument is returned as |
| 3035 | result. This function is called @code{list*} in some other |
| 3036 | Schemes and in Common LISP. |
| 3037 | @end deffn |
| 3038 | |
| 3039 | @deffn primitive list-copy lst |
| 3040 | Return a (newly-created) copy of @var{lst}. |
| 3041 | @end deffn |
| 3042 | |
| 3043 | @deffn procedure make-list n [init] |
| 3044 | Create a list containing of @var{n} elements, where each element is |
| 3045 | initialized to @var{init}. @var{init} defaults to the empty list |
| 3046 | @code{()} if not given. |
| 3047 | @end deffn |
| 3048 | |
| 3049 | Note that @code{list-copy} only makes a copy of the pairs which make up |
| 3050 | the spine of the lists. The list elements are not copied, which means |
| 3051 | that modifying the elements of the new list also modyfies the elements |
| 3052 | of the old list. On the other hand, applying procedures like |
| 3053 | @code{set-cdr!} or @code{delv!} to the new list will not alter the old |
| 3054 | list. If you also need to copy the list elements (making a deep copy), |
| 3055 | use the procedure @code{copy-tree} (@pxref{Copying}). |
| 3056 | |
| 3057 | @node List Selection |
| 3058 | @subsection List Selection |
| 3059 | |
| 3060 | @c FIXME::martin: Review me! |
| 3061 | |
| 3062 | These procedures are used to get some information about a list, or to |
| 3063 | retrieve one or more elements of a list. |
| 3064 | |
| 3065 | @rnindex length |
| 3066 | @deffn primitive length lst |
| 3067 | Return the number of elements in list @var{lst}. |
| 3068 | @end deffn |
| 3069 | |
| 3070 | @deffn primitive last-pair lst |
| 3071 | Return a pointer to the last pair in @var{lst}, signalling an error if |
| 3072 | @var{lst} is circular. |
| 3073 | @end deffn |
| 3074 | |
| 3075 | @rnindex list-ref |
| 3076 | @deffn primitive list-ref list k |
| 3077 | Return the @var{k}th element from @var{list}. |
| 3078 | @end deffn |
| 3079 | |
| 3080 | @rnindex list-tail |
| 3081 | @deffn primitive list-tail lst k |
| 3082 | @deffnx primitive list-cdr-ref lst k |
| 3083 | Return the "tail" of @var{lst} beginning with its @var{k}th element. |
| 3084 | The first element of the list is considered to be element 0. |
| 3085 | |
| 3086 | @code{list-tail} and @code{list-cdr-ref} are identical. It may help to |
| 3087 | think of @code{list-cdr-ref} as accessing the @var{k}th cdr of the list, |
| 3088 | or returning the results of cdring @var{k} times down @var{lst}. |
| 3089 | @end deffn |
| 3090 | |
| 3091 | @deffn primitive list-head lst k |
| 3092 | Copy the first @var{k} elements from @var{lst} into a new list, and |
| 3093 | return it. |
| 3094 | @end deffn |
| 3095 | |
| 3096 | @node Append/Reverse |
| 3097 | @subsection Append and Reverse |
| 3098 | |
| 3099 | @c FIXME::martin: Review me! |
| 3100 | |
| 3101 | @code{append} and @code{append!} are used to concatenate two or more |
| 3102 | lists in order to form a new list. @code{reverse} and @code{reverse!} |
| 3103 | return lists with the same elements as their arguments, but in reverse |
| 3104 | order. The procedure variants with an @code{!} directly modify the |
| 3105 | pairs which form the list, whereas the other procedures create new |
| 3106 | pairs. This is why you should be careful when using the side-effecting |
| 3107 | variants. |
| 3108 | |
| 3109 | @rnindex append |
| 3110 | @deffn primitive append . args |
| 3111 | Return a list consisting of the elements the lists passed as |
| 3112 | arguments. |
| 3113 | @lisp |
| 3114 | (append '(x) '(y)) @result{} (x y) |
| 3115 | (append '(a) '(b c d)) @result{} (a b c d) |
| 3116 | (append '(a (b)) '((c))) @result{} (a (b) (c)) |
| 3117 | @end lisp |
| 3118 | The resulting list is always newly allocated, except that it |
| 3119 | shares structure with the last list argument. The last |
| 3120 | argument may actually be any object; an improper list results |
| 3121 | if the last argument is not a proper list. |
| 3122 | @lisp |
| 3123 | (append '(a b) '(c . d)) @result{} (a b c . d) |
| 3124 | (append '() 'a) @result{} a |
| 3125 | @end lisp |
| 3126 | @end deffn |
| 3127 | |
| 3128 | @deffn primitive append! . lists |
| 3129 | A destructive version of @code{append} (@pxref{Pairs and |
| 3130 | lists,,,r5rs, The Revised^5 Report on Scheme}). The cdr field |
| 3131 | of each list's final pair is changed to point to the head of |
| 3132 | the next list, so no consing is performed. Return a pointer to |
| 3133 | the mutated list. |
| 3134 | @end deffn |
| 3135 | |
| 3136 | @rnindex reverse |
| 3137 | @deffn primitive reverse lst |
| 3138 | Return a new list that contains the elements of @var{lst} but |
| 3139 | in reverse order. |
| 3140 | @end deffn |
| 3141 | |
| 3142 | @c NJFIXME explain new_tail |
| 3143 | @deffn primitive reverse! lst [new_tail] |
| 3144 | A destructive version of @code{reverse} (@pxref{Pairs and lists,,,r5rs, |
| 3145 | The Revised^5 Report on Scheme}). The cdr of each cell in @var{lst} is |
| 3146 | modified to point to the previous list element. Return a pointer to the |
| 3147 | head of the reversed list. |
| 3148 | |
| 3149 | Caveat: because the list is modified in place, the tail of the original |
| 3150 | list now becomes its head, and the head of the original list now becomes |
| 3151 | the tail. Therefore, the @var{lst} symbol to which the head of the |
| 3152 | original list was bound now points to the tail. To ensure that the head |
| 3153 | of the modified list is not lost, it is wise to save the return value of |
| 3154 | @code{reverse!} |
| 3155 | @end deffn |
| 3156 | |
| 3157 | @node List Modifification |
| 3158 | @subsection List Modification |
| 3159 | |
| 3160 | @c FIXME::martin: Review me! |
| 3161 | |
| 3162 | The following procedures modify existing list. @code{list-set!} and |
| 3163 | @code{list-cdr-set!} change which elements a list contains, the various |
| 3164 | deletion procedures @code{delq}, @code{delv} etc. |
| 3165 | |
| 3166 | @deffn primitive list-set! list k val |
| 3167 | Set the @var{k}th element of @var{list} to @var{val}. |
| 3168 | @end deffn |
| 3169 | |
| 3170 | @deffn primitive list-cdr-set! list k val |
| 3171 | Set the @var{k}th cdr of @var{list} to @var{val}. |
| 3172 | @end deffn |
| 3173 | |
| 3174 | @deffn primitive delq item lst |
| 3175 | Return a newly-created copy of @var{lst} with elements |
| 3176 | @code{eq?} to @var{item} removed. This procedure mirrors |
| 3177 | @code{memq}: @code{delq} compares elements of @var{lst} against |
| 3178 | @var{item} with @code{eq?}. |
| 3179 | @end deffn |
| 3180 | |
| 3181 | @deffn primitive delv item lst |
| 3182 | Return a newly-created copy of @var{lst} with elements |
| 3183 | @code{eqv?} to @var{item} removed. This procedure mirrors |
| 3184 | @code{memv}: @code{delv} compares elements of @var{lst} against |
| 3185 | @var{item} with @code{eqv?}. |
| 3186 | @end deffn |
| 3187 | |
| 3188 | @deffn primitive delete item lst |
| 3189 | Return a newly-created copy of @var{lst} with elements |
| 3190 | @code{equal?} to @var{item} removed. This procedure mirrors |
| 3191 | @code{member}: @code{delete} compares elements of @var{lst} |
| 3192 | against @var{item} with @code{equal?}. |
| 3193 | @end deffn |
| 3194 | |
| 3195 | @deffn primitive delq! item lst |
| 3196 | @deffnx primitive delv! item lst |
| 3197 | @deffnx primitive delete! item lst |
| 3198 | These procedures are destructive versions of @code{delq}, @code{delv} |
| 3199 | and @code{delete}: they modify the pointers in the existing @var{lst} |
| 3200 | rather than creating a new list. Caveat evaluator: Like other |
| 3201 | destructive list functions, these functions cannot modify the binding of |
| 3202 | @var{lst}, and so cannot be used to delete the first element of |
| 3203 | @var{lst} destructively. |
| 3204 | @end deffn |
| 3205 | |
| 3206 | @deffn primitive delq1! item lst |
| 3207 | Like @code{delq!}, but only deletes the first occurrence of |
| 3208 | @var{item} from @var{lst}. Tests for equality using |
| 3209 | @code{eq?}. See also @code{delv1!} and @code{delete1!}. |
| 3210 | @end deffn |
| 3211 | |
| 3212 | @deffn primitive delv1! item lst |
| 3213 | Like @code{delv!}, but only deletes the first occurrence of |
| 3214 | @var{item} from @var{lst}. Tests for equality using |
| 3215 | @code{eqv?}. See also @code{delq1!} and @code{delete1!}. |
| 3216 | @end deffn |
| 3217 | |
| 3218 | @deffn primitive delete1! item lst |
| 3219 | Like @code{delete!}, but only deletes the first occurrence of |
| 3220 | @var{item} from @var{lst}. Tests for equality using |
| 3221 | @code{equal?}. See also @code{delq1!} and @code{delv1!}. |
| 3222 | @end deffn |
| 3223 | |
| 3224 | @node List Searching |
| 3225 | @subsection List Searching |
| 3226 | |
| 3227 | @c FIXME::martin: Review me! |
| 3228 | |
| 3229 | The following procedures search lists for particular elements. They use |
| 3230 | different comparison predicates for comparing list elements with the |
| 3231 | object to be seached. When they fail, they return @code{#f}, otherwise |
| 3232 | they return the sublist whose car is equal to the search object, where |
| 3233 | equality depends on the equality predicate used. |
| 3234 | |
| 3235 | @rnindex memq |
| 3236 | @deffn primitive memq x lst |
| 3237 | Return the first sublist of @var{lst} whose car is @code{eq?} |
| 3238 | to @var{x} where the sublists of @var{lst} are the non-empty |
| 3239 | lists returned by @code{(list-tail @var{lst} @var{k})} for |
| 3240 | @var{k} less than the length of @var{lst}. If @var{x} does not |
| 3241 | occur in @var{lst}, then @code{#f} (not the empty list) is |
| 3242 | returned. |
| 3243 | @end deffn |
| 3244 | |
| 3245 | @rnindex memv |
| 3246 | @deffn primitive memv x lst |
| 3247 | Return the first sublist of @var{lst} whose car is @code{eqv?} |
| 3248 | to @var{x} where the sublists of @var{lst} are the non-empty |
| 3249 | lists returned by @code{(list-tail @var{lst} @var{k})} for |
| 3250 | @var{k} less than the length of @var{lst}. If @var{x} does not |
| 3251 | occur in @var{lst}, then @code{#f} (not the empty list) is |
| 3252 | returned. |
| 3253 | @end deffn |
| 3254 | |
| 3255 | @rnindex member |
| 3256 | @deffn primitive member x lst |
| 3257 | Return the first sublist of @var{lst} whose car is |
| 3258 | @code{equal?} to @var{x} where the sublists of @var{lst} are |
| 3259 | the non-empty lists returned by @code{(list-tail @var{lst} |
| 3260 | @var{k})} for @var{k} less than the length of @var{lst}. If |
| 3261 | @var{x} does not occur in @var{lst}, then @code{#f} (not the |
| 3262 | empty list) is returned. |
| 3263 | @end deffn |
| 3264 | |
| 3265 | [FIXME: is there any reason to have the `sloppy' functions available at |
| 3266 | high level at all? Maybe these docs should be relegated to a "Guile |
| 3267 | Internals" node or something. -twp] |
| 3268 | |
| 3269 | @deffn primitive sloppy-memq x lst |
| 3270 | This procedure behaves like @code{memq}, but does no type or error checking. |
| 3271 | Its use is recommended only in writing Guile internals, |
| 3272 | not for high-level Scheme programs. |
| 3273 | @end deffn |
| 3274 | |
| 3275 | @deffn primitive sloppy-memv x lst |
| 3276 | This procedure behaves like @code{memv}, but does no type or error checking. |
| 3277 | Its use is recommended only in writing Guile internals, |
| 3278 | not for high-level Scheme programs. |
| 3279 | @end deffn |
| 3280 | |
| 3281 | @deffn primitive sloppy-member x lst |
| 3282 | This procedure behaves like @code{member}, but does no type or error checking. |
| 3283 | Its use is recommended only in writing Guile internals, |
| 3284 | not for high-level Scheme programs. |
| 3285 | @end deffn |
| 3286 | |
| 3287 | @node List Mapping |
| 3288 | @subsection List Mapping |
| 3289 | |
| 3290 | @c FIXME::martin: Review me! |
| 3291 | |
| 3292 | List processing is very convenient in Scheme because the process of |
| 3293 | iterating over the elements of a list can be highly abstracted. The |
| 3294 | procedures in this section are the most basic iterating procedures for |
| 3295 | lists. They take a procedure and one or more lists as arguments, and |
| 3296 | apply the procedure to each element of the list. They differ in what |
| 3297 | the result of the invocation is. |
| 3298 | |
| 3299 | @rnindex map |
| 3300 | @c begin (texi-doc-string "guile" "map") |
| 3301 | @deffn primitive map proc arg1 arg2 @dots{} |
| 3302 | @deffnx primitive map-in-order proc arg1 arg2 @dots{} |
| 3303 | Apply @var{proc} to each element of the list @var{arg1} (if only two |
| 3304 | arguments are given), or to the corresponding elements of the argument |
| 3305 | lists (if more than two arguments are given). The result(s) of the |
| 3306 | procedure applications are saved and returned in a list. For |
| 3307 | @code{map}, the order of procedure applications is not specified, |
| 3308 | @code{map-in-order} applies the procedure from left to right to the list |
| 3309 | elements. |
| 3310 | @end deffn |
| 3311 | |
| 3312 | @rnindex for-each |
| 3313 | @c begin (texi-doc-string "guile" "for-each") |
| 3314 | @deffn primitive for-each proc arg1 arg2 @dots{} |
| 3315 | Like @code{map}, but the procedure is always applied from left to right, |
| 3316 | and the result(s) of the procedure applications are thrown away. The |
| 3317 | return value is not specified. |
| 3318 | @end deffn |
| 3319 | |
| 3320 | |
| 3321 | @node Vectors |
| 3322 | @section Vectors |
| 3323 | @tpindex Vectors |
| 3324 | |
| 3325 | @c FIXME::martin: Review me! |
| 3326 | |
| 3327 | @c FIXME::martin: Should the subsections of this section be nodes |
| 3328 | @c of their own, or are the resulting nodes too short, then? |
| 3329 | |
| 3330 | Vectors are sequences of Scheme objects. Unlike lists, the length of a |
| 3331 | vector, once the vector is created, cannot be changed. The advantage of |
| 3332 | vectors over lists is that the time required to access one element of a |
| 3333 | vector is constant, whereas lists have an access time linear to the |
| 3334 | index of the accessed element in the list. |
| 3335 | |
| 3336 | Note that the vectors documented in this section can contain any kind of |
| 3337 | Scheme object, it is even possible to have different types of objects in |
| 3338 | the same vector. |
| 3339 | |
| 3340 | @subsection Vector Read Syntax |
| 3341 | |
| 3342 | Vectors can literally be entered in source code, just like strings, |
| 3343 | characters or some of the other data types. The read syntax for vectors |
| 3344 | is as follows: A sharp sign (@code{#}), followed by an opening |
| 3345 | parentheses, all elements of the vector in their respective read syntax, |
| 3346 | and finally a closing parentheses. The following are examples of the |
| 3347 | read syntax for vectors; where the first vector only contains numbers |
| 3348 | and the second three different object types: a string, a symbol and a |
| 3349 | number in hexidecimal notation. |
| 3350 | |
| 3351 | @lisp |
| 3352 | #(1 2 3) |
| 3353 | #("Hello" foo #xdeadbeef) |
| 3354 | @end lisp |
| 3355 | |
| 3356 | @subsection Vector Predicates |
| 3357 | |
| 3358 | @rnindex vector? |
| 3359 | @deffn primitive vector? obj |
| 3360 | Return @code{#t} if @var{obj} is a vector, otherwise return |
| 3361 | @code{#f}. |
| 3362 | @end deffn |
| 3363 | |
| 3364 | @subsection Vector Constructors |
| 3365 | |
| 3366 | @rnindex make-vector |
| 3367 | @deffn primitive make-vector k [fill] |
| 3368 | Return a newly allocated vector of @var{k} elements. If a |
| 3369 | second argument is given, then each element is initialized to |
| 3370 | @var{fill}. Otherwise the initial contents of each element is |
| 3371 | unspecified. |
| 3372 | @end deffn |
| 3373 | |
| 3374 | @rnindex vector |
| 3375 | @rnindex list->vector |
| 3376 | @deffn primitive vector . l |
| 3377 | @deffnx primitive list->vector l |
| 3378 | Return a newly allocated vector whose elements contain the |
| 3379 | given arguments. Analogous to @code{list}. |
| 3380 | |
| 3381 | @lisp |
| 3382 | (vector 'a 'b 'c) @result{} #(a b c) |
| 3383 | @end lisp |
| 3384 | @end deffn |
| 3385 | |
| 3386 | @rnindex vector->list |
| 3387 | @deffn primitive vector->list v |
| 3388 | Return a newly allocated list of the objects contained in the |
| 3389 | elements of @var{vector}. |
| 3390 | |
| 3391 | @lisp |
| 3392 | (vector->list '#(dah dah didah)) @result{} (dah dah didah) |
| 3393 | (list->vector '(dididit dah)) @result{} #(dididit dah) |
| 3394 | @end lisp |
| 3395 | @end deffn |
| 3396 | |
| 3397 | @subsection Vector Modification |
| 3398 | |
| 3399 | A vector created by any of the vector constructor procedures |
| 3400 | (@pxref{Vectors}) documented above can be modified using the |
| 3401 | following procedures. |
| 3402 | |
| 3403 | According to R5RS, using any of these procedures on literally entered |
| 3404 | vectors is an error, because these vectors are considered to be |
| 3405 | constant, although Guile currently does not detect this error. |
| 3406 | |
| 3407 | @rnindex vector-set! |
| 3408 | @deffn primitive vector-set! vector k obj |
| 3409 | @var{k} must be a valid index of @var{vector}. |
| 3410 | @code{Vector-set!} stores @var{obj} in element @var{k} of @var{vector}. |
| 3411 | The value returned by @samp{vector-set!} is unspecified. |
| 3412 | @lisp |
| 3413 | (let ((vec (vector 0 '(2 2 2 2) "Anna"))) |
| 3414 | (vector-set! vec 1 '("Sue" "Sue")) |
| 3415 | vec) @result{} #(0 ("Sue" "Sue") "Anna") |
| 3416 | (vector-set! '#(0 1 2) 1 "doe") @result{} @emph{error} ; constant vector |
| 3417 | @end lisp |
| 3418 | @end deffn |
| 3419 | |
| 3420 | @rnindex vector-fill! |
| 3421 | @deffn primitive vector-fill! v fill |
| 3422 | Store @var{fill} in every element of @var{vector}. The value |
| 3423 | returned by @code{vector-fill!} is unspecified. |
| 3424 | @end deffn |
| 3425 | |
| 3426 | @deffn primitive vector-move-left! vec1 start1 end1 vec2 start2 |
| 3427 | Vector version of @code{substring-move-left!}. |
| 3428 | @end deffn |
| 3429 | |
| 3430 | @deffn primitive vector-move-right! vec1 start1 end1 vec2 start2 |
| 3431 | Vector version of @code{substring-move-right!}. |
| 3432 | @end deffn |
| 3433 | |
| 3434 | @subsection Vector Selection |
| 3435 | |
| 3436 | These procedures return information about a given vector, such as the |
| 3437 | size or what elements are contained in the vector. |
| 3438 | |
| 3439 | @rnindex vector-length |
| 3440 | @deffn primitive vector-length vector |
| 3441 | Returns the number of elements in @var{vector} as an exact integer. |
| 3442 | @end deffn |
| 3443 | |
| 3444 | @rnindex vector-ref |
| 3445 | @deffn primitive vector-ref vector k |
| 3446 | @var{k} must be a valid index of @var{vector}. |
| 3447 | @samp{Vector-ref} returns the contents of element @var{k} of |
| 3448 | @var{vector}. |
| 3449 | @lisp |
| 3450 | (vector-ref '#(1 1 2 3 5 8 13 21) 5) @result{} 8 |
| 3451 | (vector-ref '#(1 1 2 3 5 8 13 21) |
| 3452 | (let ((i (round (* 2 (acos -1))))) |
| 3453 | (if (inexact? i) |
| 3454 | (inexact->exact i) |
| 3455 | i))) @result{} 13 |
| 3456 | @end lisp |
| 3457 | @end deffn |
| 3458 | |
| 3459 | |
| 3460 | @node Records |
| 3461 | @section Records |
| 3462 | |
| 3463 | [FIXME: this is pasted in from Tom Lord's original guile.texi and should |
| 3464 | be reviewed] |
| 3465 | |
| 3466 | A @dfn{record type} is a first class object representing a user-defined |
| 3467 | data type. A @dfn{record} is an instance of a record type. |
| 3468 | |
| 3469 | @deffn procedure record? obj |
| 3470 | Returns @code{#t} if @var{obj} is a record of any type and @code{#f} |
| 3471 | otherwise. |
| 3472 | |
| 3473 | Note that @code{record?} may be true of any Scheme value; there is no |
| 3474 | promise that records are disjoint with other Scheme types. |
| 3475 | @end deffn |
| 3476 | |
| 3477 | @deffn procedure make-record-type type-name field-names |
| 3478 | Returns a @dfn{record-type descriptor}, a value representing a new data |
| 3479 | type disjoint from all others. The @var{type-name} argument must be a |
| 3480 | string, but is only used for debugging purposes (such as the printed |
| 3481 | representation of a record of the new type). The @var{field-names} |
| 3482 | argument is a list of symbols naming the @dfn{fields} of a record of the |
| 3483 | new type. It is an error if the list contains any duplicates. It is |
| 3484 | unspecified how record-type descriptors are represented.@refill |
| 3485 | @end deffn |
| 3486 | |
| 3487 | @deffn procedure record-constructor rtd [field-names] |
| 3488 | Returns a procedure for constructing new members of the type represented |
| 3489 | by @var{rtd}. The returned procedure accepts exactly as many arguments |
| 3490 | as there are symbols in the given list, @var{field-names}; these are |
| 3491 | used, in order, as the initial values of those fields in a new record, |
| 3492 | which is returned by the constructor procedure. The values of any |
| 3493 | fields not named in that list are unspecified. The @var{field-names} |
| 3494 | argument defaults to the list of field names in the call to |
| 3495 | @code{make-record-type} that created the type represented by @var{rtd}; |
| 3496 | if the @var{field-names} argument is provided, it is an error if it |
| 3497 | contains any duplicates or any symbols not in the default list.@refill |
| 3498 | @end deffn |
| 3499 | |
| 3500 | @deffn procedure record-predicate rtd |
| 3501 | Returns a procedure for testing membership in the type represented by |
| 3502 | @var{rtd}. The returned procedure accepts exactly one argument and |
| 3503 | returns a true value if the argument is a member of the indicated record |
| 3504 | type; it returns a false value otherwise.@refill |
| 3505 | @end deffn |
| 3506 | |
| 3507 | @deffn procedure record-accessor rtd field-name |
| 3508 | Returns a procedure for reading the value of a particular field of a |
| 3509 | member of the type represented by @var{rtd}. The returned procedure |
| 3510 | accepts exactly one argument which must be a record of the appropriate |
| 3511 | type; it returns the current value of the field named by the symbol |
| 3512 | @var{field-name} in that record. The symbol @var{field-name} must be a |
| 3513 | member of the list of field-names in the call to @code{make-record-type} |
| 3514 | that created the type represented by @var{rtd}.@refill |
| 3515 | @end deffn |
| 3516 | |
| 3517 | @deffn procedure record-modifier rtd field-name |
| 3518 | Returns a procedure for writing the value of a particular field of a |
| 3519 | member of the type represented by @var{rtd}. The returned procedure |
| 3520 | accepts exactly two arguments: first, a record of the appropriate type, |
| 3521 | and second, an arbitrary Scheme value; it modifies the field named by |
| 3522 | the symbol @var{field-name} in that record to contain the given value. |
| 3523 | The returned value of the modifier procedure is unspecified. The symbol |
| 3524 | @var{field-name} must be a member of the list of field-names in the call |
| 3525 | to @code{make-record-type} that created the type represented by |
| 3526 | @var{rtd}.@refill |
| 3527 | @end deffn |
| 3528 | |
| 3529 | @deffn procedure record-type-descriptor record |
| 3530 | Returns a record-type descriptor representing the type of the given |
| 3531 | record. That is, for example, if the returned descriptor were passed to |
| 3532 | @code{record-predicate}, the resulting predicate would return a true |
| 3533 | value when passed the given record. Note that it is not necessarily the |
| 3534 | case that the returned descriptor is the one that was passed to |
| 3535 | @code{record-constructor} in the call that created the constructor |
| 3536 | procedure that created the given record.@refill |
| 3537 | @end deffn |
| 3538 | |
| 3539 | @deffn procedure record-type-name rtd |
| 3540 | Returns the type-name associated with the type represented by rtd. The |
| 3541 | returned value is @code{eqv?} to the @var{type-name} argument given in |
| 3542 | the call to @code{make-record-type} that created the type represented by |
| 3543 | @var{rtd}.@refill |
| 3544 | @end deffn |
| 3545 | |
| 3546 | @deffn procedure record-type-fields rtd |
| 3547 | Returns a list of the symbols naming the fields in members of the type |
| 3548 | represented by @var{rtd}. The returned value is @code{equal?} to the |
| 3549 | field-names argument given in the call to @code{make-record-type} that |
| 3550 | created the type represented by @var{rtd}.@refill |
| 3551 | @end deffn |
| 3552 | |
| 3553 | |
| 3554 | @node Structures |
| 3555 | @section Structures |
| 3556 | @tpindex Structures |
| 3557 | |
| 3558 | [FIXME: this is pasted in from Tom Lord's original guile.texi and should |
| 3559 | be reviewed] |
| 3560 | |
| 3561 | A @dfn{structure type} is a first class user-defined data type. A |
| 3562 | @dfn{structure} is an instance of a structure type. A structure type is |
| 3563 | itself a structure. |
| 3564 | |
| 3565 | Structures are less abstract and more general than traditional records. |
| 3566 | In fact, in Guile Scheme, records are implemented using structures. |
| 3567 | |
| 3568 | @menu |
| 3569 | * Structure Concepts:: The structure of Structures |
| 3570 | * Structure Layout:: Defining the layout of structure types |
| 3571 | * Structure Basics:: make-, -ref and -set! procedures for structs |
| 3572 | * Vtables:: Accessing type-specific data |
| 3573 | @end menu |
| 3574 | |
| 3575 | @node Structure Concepts |
| 3576 | @subsection Structure Concepts |
| 3577 | |
| 3578 | A structure object consists of a handle, structure data, and a vtable. |
| 3579 | The handle is a Scheme value which points to both the vtable and the |
| 3580 | structure's data. Structure data is a dynamically allocated region of |
| 3581 | memory, private to the structure, divided up into typed fields. A |
| 3582 | vtable is another structure used to hold type-specific data. Multiple |
| 3583 | structures can share a common vtable. |
| 3584 | |
| 3585 | Three concepts are key to understanding structures. |
| 3586 | |
| 3587 | @itemize @bullet{} |
| 3588 | @item @dfn{layout specifications} |
| 3589 | |
| 3590 | Layout specifications determine how memory allocated to structures is |
| 3591 | divided up into fields. Programmers must write a layout specification |
| 3592 | whenever a new type of structure is defined. |
| 3593 | |
| 3594 | @item @dfn{structural accessors} |
| 3595 | |
| 3596 | Structure access is by field number. There is only one set of |
| 3597 | accessors common to all structure objects. |
| 3598 | |
| 3599 | @item @dfn{vtables} |
| 3600 | |
| 3601 | Vtables, themselves structures, are first class representations of |
| 3602 | disjoint sub-types of structures in general. In most cases, when a |
| 3603 | new structure is created, programmers must specifiy a vtable for the |
| 3604 | new structure. Each vtable has a field describing the layout of its |
| 3605 | instances. Vtables can have additional, user-defined fields as well. |
| 3606 | @end itemize |
| 3607 | |
| 3608 | |
| 3609 | |
| 3610 | @node Structure Layout |
| 3611 | @subsection Structure Layout |
| 3612 | |
| 3613 | When a structure is created, a region of memory is allocated to hold its |
| 3614 | state. The @dfn{layout} of the structure's type determines how that |
| 3615 | memory is divided into fields. |
| 3616 | |
| 3617 | Each field has a specified type. There are only three types allowed, each |
| 3618 | corresponding to a one letter code. The allowed types are: |
| 3619 | |
| 3620 | @itemize @bullet{} |
| 3621 | @item 'u' -- unprotected |
| 3622 | |
| 3623 | The field holds binary data that is not GC protected. |
| 3624 | |
| 3625 | @item 'p' -- protected |
| 3626 | |
| 3627 | The field holds a Scheme value and is GC protected. |
| 3628 | |
| 3629 | @item 's' -- self |
| 3630 | |
| 3631 | The field holds a Scheme value and is GC protected. When a structure is |
| 3632 | created with this type of field, the field is initialized to refer to |
| 3633 | the structure's own handle. This kind of field is mainly useful when |
| 3634 | mixing Scheme and C code in which the C code may need to compute a |
| 3635 | structure's handle given only the address of its malloced data. |
| 3636 | @end itemize |
| 3637 | |
| 3638 | |
| 3639 | Each field also has an associated access protection. There are only |
| 3640 | three kinds of protection, each corresponding to a one letter code. |
| 3641 | The allowed protections are: |
| 3642 | |
| 3643 | @itemize @bullet{} |
| 3644 | @item 'w' -- writable |
| 3645 | |
| 3646 | The field can be read and written. |
| 3647 | |
| 3648 | @item 'r' -- readable |
| 3649 | |
| 3650 | The field can be read, but not written. |
| 3651 | |
| 3652 | @item 'o' -- opaque |
| 3653 | |
| 3654 | The field can be neither read nor written. This kind |
| 3655 | of protection is for fields useful only to built-in routines. |
| 3656 | @end itemize |
| 3657 | |
| 3658 | A layout specification is described by stringing together pairs |
| 3659 | of letters: one to specify a field type and one to specify a field |
| 3660 | protection. For example, a traditional cons pair type object could |
| 3661 | be described as: |
| 3662 | |
| 3663 | @example |
| 3664 | ; cons pairs have two writable fields of Scheme data |
| 3665 | "pwpw" |
| 3666 | @end example |
| 3667 | |
| 3668 | A pair object in which the first field is held constant could be: |
| 3669 | |
| 3670 | @example |
| 3671 | "prpw" |
| 3672 | @end example |
| 3673 | |
| 3674 | Binary fields, (fields of type "u"), hold one @emph{word} each. The |
| 3675 | size of a word is a machine dependent value defined to be equal to the |
| 3676 | value of the C expression: @code{sizeof (long)}. |
| 3677 | |
| 3678 | The last field of a structure layout may specify a tail array. |
| 3679 | A tail array is indicated by capitalizing the field's protection |
| 3680 | code ('W', 'R' or 'O'). A tail-array field is replaced by |
| 3681 | a read-only binary data field containing an array size. The array |
| 3682 | size is determined at the time the structure is created. It is followed |
| 3683 | by a corresponding number of fields of the type specified for the |
| 3684 | tail array. For example, a conventional Scheme vector can be |
| 3685 | described as: |
| 3686 | |
| 3687 | @example |
| 3688 | ; A vector is an arbitrary number of writable fields holding Scheme |
| 3689 | ; values: |
| 3690 | "pW" |
| 3691 | @end example |
| 3692 | |
| 3693 | In the above example, field 0 contains the size of the vector and |
| 3694 | fields beginning at 1 contain the vector elements. |
| 3695 | |
| 3696 | A kind of tagged vector (a constant tag followed by conventioal |
| 3697 | vector elements) might be: |
| 3698 | |
| 3699 | @example |
| 3700 | "prpW" |
| 3701 | @end example |
| 3702 | |
| 3703 | |
| 3704 | Structure layouts are represented by specially interned symbols whose |
| 3705 | name is a string of type and protection codes. To create a new |
| 3706 | structure layout, use this procedure: |
| 3707 | |
| 3708 | @deffn primitive make-struct-layout fields |
| 3709 | Return a new structure layout object. |
| 3710 | |
| 3711 | @var{fields} must be a string made up of pairs of characters |
| 3712 | strung together. The first character of each pair describes a field |
| 3713 | type, the second a field protection. Allowed types are 'p' for |
| 3714 | GC-protected Scheme data, 'u' for unprotected binary data, and 's' for |
| 3715 | a field that points to the structure itself. Allowed protections |
| 3716 | are 'w' for mutable fields, 'r' for read-only fields, and 'o' for opaque |
| 3717 | fields. The last field protection specification may be capitalized to |
| 3718 | indicate that the field is a tail-array. |
| 3719 | @end deffn |
| 3720 | |
| 3721 | |
| 3722 | |
| 3723 | @node Structure Basics |
| 3724 | @subsection Structure Basics |
| 3725 | |
| 3726 | This section describes the basic procedures for creating and accessing |
| 3727 | structures. |
| 3728 | |
| 3729 | @deffn primitive make-struct vtable tail_array_size . init |
| 3730 | Create a new structure. |
| 3731 | |
| 3732 | @var{type} must be a vtable structure (@pxref{Vtables}). |
| 3733 | |
| 3734 | @var{tail-elts} must be a non-negative integer. If the layout |
| 3735 | specification indicated by @var{type} includes a tail-array, |
| 3736 | this is the number of elements allocated to that array. |
| 3737 | |
| 3738 | The @var{init1}, @dots{} are optional arguments describing how |
| 3739 | successive fields of the structure should be initialized. Only fields |
| 3740 | with protection 'r' or 'w' can be initialized, except for fields of |
| 3741 | type 's', which are automatically initialized to point to the new |
| 3742 | structure itself; fields with protection 'o' can not be initialized by |
| 3743 | Scheme programs. |
| 3744 | |
| 3745 | If fewer optional arguments than initializable fields are supplied, |
| 3746 | fields of type 'p' get default value #f while fields of type 'u' are |
| 3747 | initialized to 0. |
| 3748 | |
| 3749 | Structs are currently the basic representation for record-like data |
| 3750 | structures in Guile. The plan is to eventually replace them with a |
| 3751 | new representation which will at the same time be easier to use and |
| 3752 | more powerful. |
| 3753 | |
| 3754 | For more information, see the documentation for @code{make-vtable-vtable}. |
| 3755 | @end deffn |
| 3756 | |
| 3757 | @deffn primitive struct? x |
| 3758 | Return @code{#t} iff @var{obj} is a structure object, else |
| 3759 | @code{#f}. |
| 3760 | @end deffn |
| 3761 | |
| 3762 | |
| 3763 | @deffn primitive struct-ref handle pos |
| 3764 | @deffnx primitive struct-set! struct n value |
| 3765 | Access (or modify) the @var{n}th field of @var{struct}. |
| 3766 | |
| 3767 | If the field is of type 'p', then it can be set to an arbitrary value. |
| 3768 | |
| 3769 | If the field is of type 'u', then it can only be set to a non-negative |
| 3770 | integer value small enough to fit in one machine word. |
| 3771 | @end deffn |
| 3772 | |
| 3773 | |
| 3774 | |
| 3775 | @node Vtables |
| 3776 | @subsection Vtables |
| 3777 | |
| 3778 | Vtables are structures that are used to represent structure types. Each |
| 3779 | vtable contains a layout specification in field |
| 3780 | @code{vtable-index-layout} -- instances of the type are laid out |
| 3781 | according to that specification. Vtables contain additional fields |
| 3782 | which are used only internally to libguile. The variable |
| 3783 | @code{vtable-offset-user} is bound to a field number. Vtable fields |
| 3784 | at that position or greater are user definable. |
| 3785 | |
| 3786 | @deffn primitive struct-vtable handle |
| 3787 | Return the vtable structure that describes the type of @var{struct}. |
| 3788 | @end deffn |
| 3789 | |
| 3790 | @deffn primitive struct-vtable? x |
| 3791 | Return @code{#t} iff obj is a vtable structure. |
| 3792 | @end deffn |
| 3793 | |
| 3794 | If you have a vtable structure, @code{V}, you can create an instance of |
| 3795 | the type it describes by using @code{(make-struct V ...)}. But where |
| 3796 | does @code{V} itself come from? One possibility is that @code{V} is an |
| 3797 | instance of a user-defined vtable type, @code{V'}, so that @code{V} is |
| 3798 | created by using @code{(make-struct V' ...)}. Another possibility is |
| 3799 | that @code{V} is an instance of the type it itself describes. Vtable |
| 3800 | structures of the second sort are created by this procedure: |
| 3801 | |
| 3802 | @deffn primitive make-vtable-vtable user_fields tail_array_size . init |
| 3803 | Return a new, self-describing vtable structure. |
| 3804 | |
| 3805 | @var{user-fields} is a string describing user defined fields of the |
| 3806 | vtable beginning at index @code{vtable-offset-user} |
| 3807 | (see @code{make-struct-layout}). |
| 3808 | |
| 3809 | @var{tail-size} specifies the size of the tail-array (if any) of |
| 3810 | this vtable. |
| 3811 | |
| 3812 | @var{init1}, @dots{} are the optional initializers for the fields of |
| 3813 | the vtable. |
| 3814 | |
| 3815 | Vtables have one initializable system field---the struct printer. |
| 3816 | This field comes before the user fields in the initializers passed |
| 3817 | to @code{make-vtable-vtable} and @code{make-struct}, and thus works as |
| 3818 | a third optional argument to @code{make-vtable-vtable} and a fourth to |
| 3819 | @code{make-struct} when creating vtables: |
| 3820 | |
| 3821 | If the value is a procedure, it will be called instead of the standard |
| 3822 | printer whenever a struct described by this vtable is printed. |
| 3823 | The procedure will be called with arguments STRUCT and PORT. |
| 3824 | |
| 3825 | The structure of a struct is described by a vtable, so the vtable is |
| 3826 | in essence the type of the struct. The vtable is itself a struct with |
| 3827 | a vtable. This could go on forever if it weren't for the |
| 3828 | vtable-vtables which are self-describing vtables, and thus terminate |
| 3829 | the chain. |
| 3830 | |
| 3831 | There are several potential ways of using structs, but the standard |
| 3832 | one is to use three kinds of structs, together building up a type |
| 3833 | sub-system: one vtable-vtable working as the root and one or several |
| 3834 | "types", each with a set of "instances". (The vtable-vtable should be |
| 3835 | compared to the class <class> which is the class of itself.) |
| 3836 | |
| 3837 | @lisp |
| 3838 | (define ball-root (make-vtable-vtable "pr" 0)) |
| 3839 | |
| 3840 | (define (make-ball-type ball-color) |
| 3841 | (make-struct ball-root 0 |
| 3842 | (make-struct-layout "pw") |
| 3843 | (lambda (ball port) |
| 3844 | (format port "#<a ~A ball owned by ~A>" |
| 3845 | (color ball) |
| 3846 | (owner ball))) |
| 3847 | ball-color)) |
| 3848 | (define (color ball) (struct-ref (struct-vtable ball) vtable-offset-user)) |
| 3849 | (define (owner ball) (struct-ref ball 0)) |
| 3850 | |
| 3851 | (define red (make-ball-type 'red)) |
| 3852 | (define green (make-ball-type 'green)) |
| 3853 | |
| 3854 | (define (make-ball type owner) (make-struct type 0 owner)) |
| 3855 | |
| 3856 | (define ball (make-ball green 'Nisse)) |
| 3857 | ball @result{} #<a green ball owned by Nisse> |
| 3858 | @end lisp |
| 3859 | @end deffn |
| 3860 | |
| 3861 | @deffn primitive struct-vtable-name vtable |
| 3862 | Return the name of the vtable @var{vtable}. |
| 3863 | @end deffn |
| 3864 | |
| 3865 | @deffn primitive set-struct-vtable-name! vtable name |
| 3866 | Set the name of the vtable @var{vtable} to @var{name}. |
| 3867 | @end deffn |
| 3868 | |
| 3869 | @deffn primitive struct-vtable-tag handle |
| 3870 | Return the vtable tag of the structure @var{handle}. |
| 3871 | @end deffn |
| 3872 | |
| 3873 | |
| 3874 | @node Arrays |
| 3875 | @section Arrays |
| 3876 | @tpindex Arrays |
| 3877 | |
| 3878 | @menu |
| 3879 | * Conventional Arrays:: Arrays with arbitrary data. |
| 3880 | * Array Mapping:: Applying a procedure to the contents of an array. |
| 3881 | * Uniform Arrays:: Arrays with data of a single type. |
| 3882 | * Bit Vectors:: Vectors of bits. |
| 3883 | @end menu |
| 3884 | |
| 3885 | @node Conventional Arrays |
| 3886 | @subsection Conventional Arrays |
| 3887 | |
| 3888 | @dfn{Conventional arrays} are a collection of cells organised into an |
| 3889 | arbitrary number of dimensions. Each cell can hold any kind of Scheme |
| 3890 | value and can be accessed in constant time by supplying an index for |
| 3891 | each dimension. This contrasts with uniform arrays, which use memory |
| 3892 | more efficiently but can hold data of only a single type, and lists |
| 3893 | where inserting and deleting cells is more efficient, but more time |
| 3894 | is usually required to access a particular cell. |
| 3895 | |
| 3896 | A conventional array is displayed as @code{#} followed by the @dfn{rank} |
| 3897 | (number of dimensions) followed by the cells, organised into dimensions |
| 3898 | using parentheses. The nesting depth of the parentheses is equal to |
| 3899 | the rank. |
| 3900 | |
| 3901 | When an array is created, the number of dimensions and range of each |
| 3902 | dimension must be specified, e.g., to create a 2x3 array with a |
| 3903 | zero-based index: |
| 3904 | |
| 3905 | @example |
| 3906 | (make-array 'ho 2 3) @result{} |
| 3907 | #2((ho ho ho) (ho ho ho)) |
| 3908 | @end example |
| 3909 | |
| 3910 | The range of each dimension can also be given explicitly, e.g., another |
| 3911 | way to create the same array: |
| 3912 | |
| 3913 | @example |
| 3914 | (make-array 'ho '(0 1) '(0 2)) @result{} |
| 3915 | #2((ho ho ho) (ho ho ho)) |
| 3916 | @end example |
| 3917 | |
| 3918 | A conventional array with one dimension based at zero is identical to |
| 3919 | a vector: |
| 3920 | |
| 3921 | @example |
| 3922 | (make-array 'ho 3) @result{} |
| 3923 | #(ho ho ho) |
| 3924 | @end example |
| 3925 | |
| 3926 | The following procedures can be used with conventional arrays (or vectors). |
| 3927 | |
| 3928 | @deffn primitive array? v [prot] |
| 3929 | Return @code{#t} if the @var{obj} is an array, and @code{#f} if |
| 3930 | not. The @var{prototype} argument is used with uniform arrays |
| 3931 | and is described elsewhere. |
| 3932 | @end deffn |
| 3933 | |
| 3934 | @deffn procedure make-array initial-value bound1 bound2 @dots{} |
| 3935 | Creates and returns an array that has as many dimensions as there are |
| 3936 | @var{bound}s and fills it with @var{initial-value}. |
| 3937 | @end deffn |
| 3938 | |
| 3939 | @c array-ref's type is `compiled-closure'. There's some weird stuff |
| 3940 | @c going on in array.c, too. Let's call it a primitive. -twp |
| 3941 | |
| 3942 | @deffn primitive uniform-vector-ref v args |
| 3943 | @deffnx primitive array-ref v . args |
| 3944 | Return the element at the @code{(index1, index2)} element in |
| 3945 | @var{array}. |
| 3946 | @end deffn |
| 3947 | |
| 3948 | @deffn primitive array-in-bounds? v . args |
| 3949 | Return @code{#t} if its arguments would be acceptable to |
| 3950 | @code{array-ref}. |
| 3951 | @end deffn |
| 3952 | |
| 3953 | @deffn primitive array-set! v obj . args |
| 3954 | @deffnx primitive uniform-array-set1! v obj args |
| 3955 | Sets the element at the @code{(index1, index2)} element in @var{array} to |
| 3956 | @var{new-value}. The value returned by array-set! is unspecified. |
| 3957 | @end deffn |
| 3958 | |
| 3959 | @deffn primitive make-shared-array oldra mapfunc . dims |
| 3960 | @code{make-shared-array} can be used to create shared subarrays of other |
| 3961 | arrays. The @var{mapper} is a function that translates coordinates in |
| 3962 | the new array into coordinates in the old array. A @var{mapper} must be |
| 3963 | linear, and its range must stay within the bounds of the old array, but |
| 3964 | it can be otherwise arbitrary. A simple example: |
| 3965 | @lisp |
| 3966 | (define fred (make-array #f 8 8)) |
| 3967 | (define freds-diagonal |
| 3968 | (make-shared-array fred (lambda (i) (list i i)) 8)) |
| 3969 | (array-set! freds-diagonal 'foo 3) |
| 3970 | (array-ref fred 3 3) @result{} foo |
| 3971 | (define freds-center |
| 3972 | (make-shared-array fred (lambda (i j) (list (+ 3 i) (+ 3 j))) 2 2)) |
| 3973 | (array-ref freds-center 0 0) @result{} foo |
| 3974 | @end lisp |
| 3975 | @end deffn |
| 3976 | |
| 3977 | @deffn primitive shared-array-increments ra |
| 3978 | For each dimension, return the distance between elements in the root vector. |
| 3979 | @end deffn |
| 3980 | |
| 3981 | @deffn primitive shared-array-offset ra |
| 3982 | Return the root vector index of the first element in the array. |
| 3983 | @end deffn |
| 3984 | |
| 3985 | @deffn primitive shared-array-root ra |
| 3986 | Return the root vector of a shared array. |
| 3987 | @end deffn |
| 3988 | |
| 3989 | @deffn primitive transpose-array ra . args |
| 3990 | Return an array sharing contents with @var{array}, but with |
| 3991 | dimensions arranged in a different order. There must be one |
| 3992 | @var{dim} argument for each dimension of @var{array}. |
| 3993 | @var{dim0}, @var{dim1}, @dots{} should be integers between 0 |
| 3994 | and the rank of the array to be returned. Each integer in that |
| 3995 | range must appear at least once in the argument list. |
| 3996 | |
| 3997 | The values of @var{dim0}, @var{dim1}, @dots{} correspond to |
| 3998 | dimensions in the array to be returned, their positions in the |
| 3999 | argument list to dimensions of @var{array}. Several @var{dim}s |
| 4000 | may have the same value, in which case the returned array will |
| 4001 | have smaller rank than @var{array}. |
| 4002 | |
| 4003 | @lisp |
| 4004 | (transpose-array '#2((a b) (c d)) 1 0) @result{} #2((a c) (b d)) |
| 4005 | (transpose-array '#2((a b) (c d)) 0 0) @result{} #1(a d) |
| 4006 | (transpose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 1 0) @result{} |
| 4007 | #2((a 4) (b 5) (c 6)) |
| 4008 | @end lisp |
| 4009 | @end deffn |
| 4010 | |
| 4011 | @deffn primitive enclose-array ra . axes |
| 4012 | @var{dim0}, @var{dim1} @dots{} should be nonnegative integers less than |
| 4013 | the rank of @var{array}. @var{enclose-array} returns an array |
| 4014 | resembling an array of shared arrays. The dimensions of each shared |
| 4015 | array are the same as the @var{dim}th dimensions of the original array, |
| 4016 | the dimensions of the outer array are the same as those of the original |
| 4017 | array that did not match a @var{dim}. |
| 4018 | |
| 4019 | An enclosed array is not a general Scheme array. Its elements may not |
| 4020 | be set using @code{array-set!}. Two references to the same element of |
| 4021 | an enclosed array will be @code{equal?} but will not in general be |
| 4022 | @code{eq?}. The value returned by @var{array-prototype} when given an |
| 4023 | enclosed array is unspecified. |
| 4024 | |
| 4025 | examples: |
| 4026 | @lisp |
| 4027 | (enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1) @result{} |
| 4028 | #<enclosed-array (#1(a d) #1(b e) #1(c f)) (#1(1 4) #1(2 5) #1(3 6))> |
| 4029 | |
| 4030 | (enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 0) @result{} |
| 4031 | #<enclosed-array #2((a 1) (d 4)) #2((b 2) (e 5)) #2((c 3) (f 6))> |
| 4032 | @end lisp |
| 4033 | @end deffn |
| 4034 | |
| 4035 | @deffn procedure array-shape array |
| 4036 | Returns a list of inclusive bounds of integers. |
| 4037 | @example |
| 4038 | (array-shape (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) (0 4)) |
| 4039 | @end example |
| 4040 | @end deffn |
| 4041 | |
| 4042 | @deffn primitive array-dimensions ra |
| 4043 | @code{Array-dimensions} is similar to @code{array-shape} but replaces |
| 4044 | elements with a @code{0} minimum with one greater than the maximum. So: |
| 4045 | @lisp |
| 4046 | (array-dimensions (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) 5) |
| 4047 | @end lisp |
| 4048 | @end deffn |
| 4049 | |
| 4050 | @deffn primitive array-rank ra |
| 4051 | Return the number of dimensions of @var{obj}. If @var{obj} is |
| 4052 | not an array, @code{0} is returned. |
| 4053 | @end deffn |
| 4054 | |
| 4055 | @deffn primitive array->list v |
| 4056 | Return a list consisting of all the elements, in order, of |
| 4057 | @var{array}. |
| 4058 | @end deffn |
| 4059 | |
| 4060 | @deffn primitive array-copy! src dst |
| 4061 | @deffnx primitive array-copy-in-order! src dst |
| 4062 | Copies every element from vector or array @var{source} to the |
| 4063 | corresponding element of @var{destination}. @var{destination} must have |
| 4064 | the same rank as @var{source}, and be at least as large in each |
| 4065 | dimension. The order is unspecified. |
| 4066 | @end deffn |
| 4067 | |
| 4068 | @deffn primitive array-fill! ra fill |
| 4069 | Stores @var{fill} in every element of @var{array}. The value returned |
| 4070 | is unspecified. |
| 4071 | @end deffn |
| 4072 | |
| 4073 | @c begin (texi-doc-string "guile" "array-equal?") |
| 4074 | @deffn primitive array-equal? ra0 ra1 |
| 4075 | Returns @code{#t} iff all arguments are arrays with the same shape, the |
| 4076 | same type, and have corresponding elements which are either |
| 4077 | @code{equal?} or @code{array-equal?}. This function differs from |
| 4078 | @code{equal?} in that a one dimensional shared array may be |
| 4079 | @var{array-equal?} but not @var{equal?} to a vector or uniform vector. |
| 4080 | @end deffn |
| 4081 | |
| 4082 | @deffn primitive array-contents ra [strict] |
| 4083 | @deffnx primitive array-contents array strict |
| 4084 | If @var{array} may be @dfn{unrolled} into a one dimensional shared array |
| 4085 | without changing their order (last subscript changing fastest), then |
| 4086 | @code{array-contents} returns that shared array, otherwise it returns |
| 4087 | @code{#f}. All arrays made by @var{make-array} and |
| 4088 | @var{make-uniform-array} may be unrolled, some arrays made by |
| 4089 | @var{make-shared-array} may not be. |
| 4090 | |
| 4091 | If the optional argument @var{strict} is provided, a shared array will |
| 4092 | be returned only if its elements are stored internally contiguous in |
| 4093 | memory. |
| 4094 | @end deffn |
| 4095 | |
| 4096 | @node Array Mapping |
| 4097 | @subsection Array Mapping |
| 4098 | |
| 4099 | @deffn primitive array-map! ra0 proc . lra |
| 4100 | @deffnx primitive array-map-in-order! ra0 proc . lra |
| 4101 | @var{array1}, @dots{} must have the same number of dimensions as |
| 4102 | @var{array0} and have a range for each index which includes the range |
| 4103 | for the corresponding index in @var{array0}. @var{proc} is applied to |
| 4104 | each tuple of elements of @var{array1} @dots{} and the result is stored |
| 4105 | as the corresponding element in @var{array0}. The value returned is |
| 4106 | unspecified. The order of application is unspecified. |
| 4107 | @end deffn |
| 4108 | |
| 4109 | @deffn primitive array-for-each proc ra0 . lra |
| 4110 | @var{proc} is applied to each tuple of elements of @var{array0} @dots{} |
| 4111 | in row-major order. The value returned is unspecified. |
| 4112 | @end deffn |
| 4113 | |
| 4114 | @deffn primitive array-index-map! ra proc |
| 4115 | applies @var{proc} to the indices of each element of @var{array} in |
| 4116 | turn, storing the result in the corresponding element. The value |
| 4117 | returned and the order of application are unspecified. |
| 4118 | |
| 4119 | One can implement @var{array-indexes} as |
| 4120 | @lisp |
| 4121 | (define (array-indexes array) |
| 4122 | (let ((ra (apply make-array #f (array-shape array)))) |
| 4123 | (array-index-map! ra (lambda x x)) |
| 4124 | ra)) |
| 4125 | @end lisp |
| 4126 | Another example: |
| 4127 | @lisp |
| 4128 | (define (apl:index-generator n) |
| 4129 | (let ((v (make-uniform-vector n 1))) |
| 4130 | (array-index-map! v (lambda (i) i)) |
| 4131 | v)) |
| 4132 | @end lisp |
| 4133 | @end deffn |
| 4134 | |
| 4135 | @node Uniform Arrays |
| 4136 | @subsection Uniform Arrays |
| 4137 | @tpindex Uniform Arrays |
| 4138 | |
| 4139 | @noindent |
| 4140 | @dfn{Uniform arrays} have elements all of the |
| 4141 | same type and occupy less storage than conventional |
| 4142 | arrays. Uniform arrays with a single zero-based dimension |
| 4143 | are also known as @dfn{uniform vectors}. The procedures in |
| 4144 | this section can also be used on conventional arrays, vectors, |
| 4145 | bit-vectors and strings. |
| 4146 | |
| 4147 | @noindent |
| 4148 | When creating a uniform array, the type of data to be stored |
| 4149 | is indicated with a @var{prototype} argument. The following table |
| 4150 | lists the types available and example prototypes: |
| 4151 | |
| 4152 | @example |
| 4153 | prototype type printing character |
| 4154 | |
| 4155 | #t boolean (bit-vector) b |
| 4156 | #\a char (string) a |
| 4157 | #\nul byte (integer) y |
| 4158 | 's short (integer) h |
| 4159 | 1 unsigned long (integer) u |
| 4160 | -1 signed long (integer) e |
| 4161 | 'l signed long long (integer) l |
| 4162 | 1.0 float (single precision) s |
| 4163 | 1/3 double (double precision float) i |
| 4164 | 0+i complex (double precision) c |
| 4165 | () conventional vector |
| 4166 | @end example |
| 4167 | |
| 4168 | @noindent |
| 4169 | Unshared uniform arrays of characters with a single zero-based dimension |
| 4170 | are identical to strings: |
| 4171 | |
| 4172 | @example |
| 4173 | (make-uniform-array #\a 3) @result{} |
| 4174 | "aaa" |
| 4175 | @end example |
| 4176 | |
| 4177 | @noindent |
| 4178 | Unshared uniform arrays of booleans with a single zero-based dimension |
| 4179 | are identical to @ref{Bit Vectors, bit-vectors}. |
| 4180 | |
| 4181 | @example |
| 4182 | (make-uniform-array #t 3) @result{} |
| 4183 | #*111 |
| 4184 | @end example |
| 4185 | |
| 4186 | @noindent |
| 4187 | Other uniform vectors are written in a form similar to that of vectors, |
| 4188 | except that a single character from the above table is put between |
| 4189 | @code{#} and @code{(}. For example, a uniform vector of signed |
| 4190 | long integers is displayed in the form @code{'#e(3 5 9)}. |
| 4191 | |
| 4192 | @deffn primitive array? v [prot] |
| 4193 | Returns @code{#t} if the @var{obj} is an array, and @code{#f} if not. |
| 4194 | |
| 4195 | The @var{prototype} argument is used with uniform arrays and is described |
| 4196 | elsewhere. |
| 4197 | @end deffn |
| 4198 | |
| 4199 | @deffn procedure make-uniform-array prototype bound1 bound2 @dots{} |
| 4200 | Creates and returns a uniform array of type corresponding to |
| 4201 | @var{prototype} that has as many dimensions as there are @var{bound}s |
| 4202 | and fills it with @var{prototype}. |
| 4203 | @end deffn |
| 4204 | |
| 4205 | @deffn primitive array-prototype ra |
| 4206 | Return an object that would produce an array of the same type |
| 4207 | as @var{array}, if used as the @var{prototype} for |
| 4208 | @code{make-uniform-array}. |
| 4209 | @end deffn |
| 4210 | |
| 4211 | @deffn primitive list->uniform-array ndim prot lst |
| 4212 | @deffnx procedure list->uniform-vector prot lst |
| 4213 | Return a uniform array of the type indicated by prototype |
| 4214 | @var{prot} with elements the same as those of @var{lst}. |
| 4215 | Elements must be of the appropriate type, no coercions are |
| 4216 | done. |
| 4217 | @end deffn |
| 4218 | |
| 4219 | @deffn primitive uniform-vector-fill! uve fill |
| 4220 | Stores @var{fill} in every element of @var{uve}. The value returned is |
| 4221 | unspecified. |
| 4222 | @end deffn |
| 4223 | |
| 4224 | @deffn primitive uniform-vector-length v |
| 4225 | Return the number of elements in @var{uve}. |
| 4226 | @end deffn |
| 4227 | |
| 4228 | @deffn primitive dimensions->uniform-array dims prot [fill] |
| 4229 | @deffnx primitive make-uniform-vector length prototype [fill] |
| 4230 | Create and return a uniform array or vector of type |
| 4231 | corresponding to @var{prototype} with dimensions @var{dims} or |
| 4232 | length @var{length}. If @var{fill} is supplied, it's used to |
| 4233 | fill the array, otherwise @var{prototype} is used. |
| 4234 | @end deffn |
| 4235 | |
| 4236 | @c Another compiled-closure. -twp |
| 4237 | |
| 4238 | @deffn primitive uniform-array-read! ra [port_or_fd [start [end]]] |
| 4239 | @deffnx primitive uniform-vector-read! uve [port-or-fdes] [start] [end] |
| 4240 | Attempts to read all elements of @var{ura}, in lexicographic order, as |
| 4241 | binary objects from @var{port-or-fdes}. |
| 4242 | If an end of file is encountered during |
| 4243 | uniform-array-read! the objects up to that point only are put into @var{ura} |
| 4244 | (starting at the beginning) and the remainder of the array is |
| 4245 | unchanged. |
| 4246 | |
| 4247 | The optional arguments @var{start} and @var{end} allow |
| 4248 | a specified region of a vector (or linearized array) to be read, |
| 4249 | leaving the remainder of the vector unchanged. |
| 4250 | |
| 4251 | @code{uniform-array-read!} returns the number of objects read. |
| 4252 | @var{port-or-fdes} may be omitted, in which case it defaults to the value |
| 4253 | returned by @code{(current-input-port)}. |
| 4254 | @end deffn |
| 4255 | |
| 4256 | @deffn primitive uniform-array-write v [port_or_fd [start [end]]] |
| 4257 | @deffnx primitive uniform-vector-write uve [port-or-fdes] [start] [end] |
| 4258 | Writes all elements of @var{ura} as binary objects to |
| 4259 | @var{port-or-fdes}. |
| 4260 | |
| 4261 | The optional arguments @var{start} |
| 4262 | and @var{end} allow |
| 4263 | a specified region of a vector (or linearized array) to be written. |
| 4264 | |
| 4265 | The number of objects actually written is returned. |
| 4266 | @var{port-or-fdes} may be |
| 4267 | omitted, in which case it defaults to the value returned by |
| 4268 | @code{(current-output-port)}. |
| 4269 | @end deffn |
| 4270 | |
| 4271 | @node Bit Vectors |
| 4272 | @subsection Bit Vectors |
| 4273 | |
| 4274 | @noindent |
| 4275 | Bit vectors are a specific type of uniform array: an array of booleans |
| 4276 | with a single zero-based index. |
| 4277 | |
| 4278 | @noindent |
| 4279 | They are displayed as a sequence of @code{0}s and |
| 4280 | @code{1}s prefixed by @code{#*}, e.g., |
| 4281 | |
| 4282 | @example |
| 4283 | (make-uniform-vector 8 #t #f) @result{} |
| 4284 | #*00000000 |
| 4285 | |
| 4286 | #b(#t #f #t) @result{} |
| 4287 | #*101 |
| 4288 | @end example |
| 4289 | |
| 4290 | @deffn primitive bit-count b bitvector |
| 4291 | Return the number of occurrences of the boolean @var{b} in |
| 4292 | @var{bitvector}. |
| 4293 | @end deffn |
| 4294 | |
| 4295 | @deffn primitive bit-position item v k |
| 4296 | Return the minimum index of an occurrence of @var{bool} in |
| 4297 | @var{bv} which is at least @var{k}. If no @var{bool} occurs |
| 4298 | within the specified range @code{#f} is returned. |
| 4299 | @end deffn |
| 4300 | |
| 4301 | @deffn primitive bit-invert! v |
| 4302 | Modifies @var{bv} by replacing each element with its negation. |
| 4303 | @end deffn |
| 4304 | |
| 4305 | @deffn primitive bit-set*! v kv obj |
| 4306 | If uve is a bit-vector @var{bv} and uve must be of the same |
| 4307 | length. If @var{bool} is @code{#t}, uve is OR'ed into |
| 4308 | @var{bv}; If @var{bool} is @code{#f}, the inversion of uve is |
| 4309 | AND'ed into @var{bv}. |
| 4310 | |
| 4311 | If uve is a unsigned long integer vector all the elements of uve |
| 4312 | must be between 0 and the @code{length} of @var{bv}. The bits |
| 4313 | of @var{bv} corresponding to the indexes in uve are set to |
| 4314 | @var{bool}. The return value is unspecified. |
| 4315 | @end deffn |
| 4316 | |
| 4317 | @deffn primitive bit-count* v kv obj |
| 4318 | Return |
| 4319 | @lisp |
| 4320 | (bit-count (bit-set*! (if bool bv (bit-invert! bv)) uve #t) #t). |
| 4321 | @end lisp |
| 4322 | @var{bv} is not modified. |
| 4323 | @end deffn |
| 4324 | |
| 4325 | |
| 4326 | @node Association Lists and Hash Tables |
| 4327 | @section Association Lists and Hash Tables |
| 4328 | |
| 4329 | This chapter discusses dictionary objects: data structures that are |
| 4330 | useful for organizing and indexing large bodies of information. |
| 4331 | |
| 4332 | @menu |
| 4333 | * Dictionary Types:: About dictionary types; what they're good for. |
| 4334 | * Association Lists:: List-based dictionaries. |
| 4335 | * Hash Tables:: Table-based dictionaries. |
| 4336 | @end menu |
| 4337 | |
| 4338 | @node Dictionary Types |
| 4339 | @subsection Dictionary Types |
| 4340 | |
| 4341 | A @dfn{dictionary} object is a data structure used to index |
| 4342 | information in a user-defined way. In standard Scheme, the main |
| 4343 | aggregate data types are lists and vectors. Lists are not really |
| 4344 | indexed at all, and vectors are indexed only by number |
| 4345 | (e.g. @code{(vector-ref foo 5)}). Often you will find it useful |
| 4346 | to index your data on some other type; for example, in a library |
| 4347 | catalog you might want to look up a book by the name of its |
| 4348 | author. Dictionaries are used to help you organize information in |
| 4349 | such a way. |
| 4350 | |
| 4351 | An @dfn{association list} (or @dfn{alist} for short) is a list of |
| 4352 | key-value pairs. Each pair represents a single quantity or |
| 4353 | object; the @code{car} of the pair is a key which is used to |
| 4354 | identify the object, and the @code{cdr} is the object's value. |
| 4355 | |
| 4356 | A @dfn{hash table} also permits you to index objects with |
| 4357 | arbitrary keys, but in a way that makes looking up any one object |
| 4358 | extremely fast. A well-designed hash system makes hash table |
| 4359 | lookups almost as fast as conventional array or vector references. |
| 4360 | |
| 4361 | Alists are popular among Lisp programmers because they use only |
| 4362 | the language's primitive operations (lists, @dfn{car}, @dfn{cdr} |
| 4363 | and the equality primitives). No changes to the language core are |
| 4364 | necessary. Therefore, with Scheme's built-in list manipulation |
| 4365 | facilities, it is very convenient to handle data stored in an |
| 4366 | association list. Also, alists are highly portable and can be |
| 4367 | easily implemented on even the most minimal Lisp systems. |
| 4368 | |
| 4369 | However, alists are inefficient, especially for storing large |
| 4370 | quantities of data. Because we want Guile to be useful for large |
| 4371 | software systems as well as small ones, Guile provides a rich set |
| 4372 | of tools for using either association lists or hash tables. |
| 4373 | |
| 4374 | @node Association Lists |
| 4375 | @subsection Association Lists |
| 4376 | @tpindex Association Lists |
| 4377 | @tpindex Alist |
| 4378 | |
| 4379 | @cindex Association List |
| 4380 | @cindex Alist |
| 4381 | @cindex Database |
| 4382 | |
| 4383 | An association list is a conventional data structure that is often used |
| 4384 | to implement simple key-value databases. It consists of a list of |
| 4385 | entries in which each entry is a pair. The @dfn{key} of each entry is |
| 4386 | the @code{car} of the pair and the @dfn{value} of each entry is the |
| 4387 | @code{cdr}. |
| 4388 | |
| 4389 | @example |
| 4390 | ASSOCIATION LIST ::= '( (KEY1 . VALUE1) |
| 4391 | (KEY2 . VALUE2) |
| 4392 | (KEY3 . VALUE3) |
| 4393 | @dots{} |
| 4394 | ) |
| 4395 | @end example |
| 4396 | |
| 4397 | @noindent |
| 4398 | Association lists are also known, for short, as @dfn{alists}. |
| 4399 | |
| 4400 | The structure of an association list is just one example of the infinite |
| 4401 | number of possible structures that can be built using pairs and lists. |
| 4402 | As such, the keys and values in an association list can be manipulated |
| 4403 | using the general list structure procedures @code{cons}, @code{car}, |
| 4404 | @code{cdr}, @code{set-car!}, @code{set-cdr!} and so on. However, |
| 4405 | because association lists are so useful, Guile also provides specific |
| 4406 | procedures for manipulating them. |
| 4407 | |
| 4408 | @menu |
| 4409 | * Alist Key Equality:: |
| 4410 | * Adding or Setting Alist Entries:: |
| 4411 | * Retrieving Alist Entries:: |
| 4412 | * Removing Alist Entries:: |
| 4413 | * Sloppy Alist Functions:: |
| 4414 | * Alist Example:: |
| 4415 | @end menu |
| 4416 | |
| 4417 | @node Alist Key Equality |
| 4418 | @subsubsection Alist Key Equality |
| 4419 | |
| 4420 | All of Guile's dedicated association list procedures, apart from |
| 4421 | @code{acons}, come in three flavours, depending on the level of equality |
| 4422 | that is required to decide whether an existing key in the association |
| 4423 | list is the same as the key that the procedure call uses to identify the |
| 4424 | required entry. |
| 4425 | |
| 4426 | @itemize @bullet |
| 4427 | @item |
| 4428 | Procedures with @dfn{assq} in their name use @code{eq?} to determine key |
| 4429 | equality. |
| 4430 | |
| 4431 | @item |
| 4432 | Procedures with @dfn{assv} in their name use @code{eqv?} to determine |
| 4433 | key equality. |
| 4434 | |
| 4435 | @item |
| 4436 | Procedures with @dfn{assoc} in their name use @code{equal?} to |
| 4437 | determine key equality. |
| 4438 | @end itemize |
| 4439 | |
| 4440 | @code{acons} is an exception because it is used to build association |
| 4441 | lists which do not require their entries' keys to be unique. |
| 4442 | |
| 4443 | @node Adding or Setting Alist Entries |
| 4444 | @subsubsection Adding or Setting Alist Entries |
| 4445 | |
| 4446 | @code{acons} adds a new entry to an association list and returns the |
| 4447 | combined association list. The combined alist is formed by consing the |
| 4448 | new entry onto the head of the alist specified in the @code{acons} |
| 4449 | procedure call. So the specified alist is not modified, but its |
| 4450 | contents become shared with the tail of the combined alist that |
| 4451 | @code{acons} returns. |
| 4452 | |
| 4453 | In the most common usage of @code{acons}, a variable holding the |
| 4454 | original association list is updated with the combined alist: |
| 4455 | |
| 4456 | @example |
| 4457 | (set! address-list (acons name address address-list)) |
| 4458 | @end example |
| 4459 | |
| 4460 | In such cases, it doesn't matter that the old and new values of |
| 4461 | @code{address-list} share some of their contents, since the old value is |
| 4462 | usually no longer independently accessible. |
| 4463 | |
| 4464 | Note that @code{acons} adds the specified new entry regardless of |
| 4465 | whether the alist may already contain entries with keys that are, in |
| 4466 | some sense, the same as that of the new entry. Thus @code{acons} is |
| 4467 | ideal for building alists where there is no concept of key uniqueness. |
| 4468 | |
| 4469 | @example |
| 4470 | (set! task-list (acons 3 "pay gas bill" '())) |
| 4471 | task-list |
| 4472 | @result{} |
| 4473 | ((3 . "pay gas bill")) |
| 4474 | |
| 4475 | (set! task-list (acons 3 "tidy bedroom" task-list)) |
| 4476 | task-list |
| 4477 | @result{} |
| 4478 | ((3 . "tidy bedroom") (3 . "pay gas bill")) |
| 4479 | @end example |
| 4480 | |
| 4481 | @code{assq-set!}, @code{assv-set!} and @code{assoc-set!} are used to add |
| 4482 | or replace an entry in an association list where there @emph{is} a |
| 4483 | concept of key uniqueness. If the specified association list already |
| 4484 | contains an entry whose key is the same as that specified in the |
| 4485 | procedure call, the existing entry is replaced by the new one. |
| 4486 | Otherwise, the new entry is consed onto the head of the old association |
| 4487 | list to create the combined alist. In all cases, these procedures |
| 4488 | return the combined alist. |
| 4489 | |
| 4490 | @code{assq-set!} and friends @emph{may} destructively modify the |
| 4491 | structure of the old association list in such a way that an existing |
| 4492 | variable is correctly updated without having to @code{set!} it to the |
| 4493 | value returned: |
| 4494 | |
| 4495 | @example |
| 4496 | address-list |
| 4497 | @result{} |
| 4498 | (("mary" . "34 Elm Road") ("james" . "16 Bow Street")) |
| 4499 | |
| 4500 | (assoc-set! address-list "james" "1a London Road") |
| 4501 | @result{} |
| 4502 | (("mary" . "34 Elm Road") ("james" . "1a London Road")) |
| 4503 | |
| 4504 | address-list |
| 4505 | @result{} |
| 4506 | (("mary" . "34 Elm Road") ("james" . "1a London Road")) |
| 4507 | @end example |
| 4508 | |
| 4509 | Or they may not: |
| 4510 | |
| 4511 | @example |
| 4512 | (assoc-set! address-list "bob" "11 Newington Avenue") |
| 4513 | @result{} |
| 4514 | (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road") |
| 4515 | ("james" . "1a London Road")) |
| 4516 | |
| 4517 | address-list |
| 4518 | @result{} |
| 4519 | (("mary" . "34 Elm Road") ("james" . "1a London Road")) |
| 4520 | @end example |
| 4521 | |
| 4522 | The only safe way to update an association list variable when adding or |
| 4523 | replacing an entry like this is to @code{set!} the variable to the |
| 4524 | returned value: |
| 4525 | |
| 4526 | @example |
| 4527 | (set! address-list |
| 4528 | (assoc-set! address-list "bob" "11 Newington Avenue")) |
| 4529 | address-list |
| 4530 | @result{} |
| 4531 | (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road") |
| 4532 | ("james" . "1a London Road")) |
| 4533 | @end example |
| 4534 | |
| 4535 | Because of this slight inconvenience, you may find it more convenient to |
| 4536 | use hash tables to store dictionary data. If your application will not |
| 4537 | be modifying the contents of an alist very often, this may not make much |
| 4538 | difference to you. |
| 4539 | |
| 4540 | If you need to keep the old value of an association list in a form |
| 4541 | independent from the list that results from modification by |
| 4542 | @code{acons}, @code{assq-set!}, @code{assv-set!} or @code{assoc-set!}, |
| 4543 | use @code{list-copy} to copy the old association list before modifying |
| 4544 | it. |
| 4545 | |
| 4546 | @deffn primitive acons key value alist |
| 4547 | Adds a new key-value pair to @var{alist}. A new pair is |
| 4548 | created whose car is @var{key} and whose cdr is @var{value}, and the |
| 4549 | pair is consed onto @var{alist}, and the new list is returned. This |
| 4550 | function is @emph{not} destructive; @var{alist} is not modified. |
| 4551 | @end deffn |
| 4552 | |
| 4553 | @deffn primitive assq-set! alist key val |
| 4554 | @deffnx primitive assv-set! alist key value |
| 4555 | @deffnx primitive assoc-set! alist key value |
| 4556 | Reassociate @var{key} in @var{alist} with @var{value}: find any existing |
| 4557 | @var{alist} entry for @var{key} and associate it with the new |
| 4558 | @var{value}. If @var{alist} does not contain an entry for @var{key}, |
| 4559 | add a new one. Return the (possibly new) alist. |
| 4560 | |
| 4561 | These functions do not attempt to verify the structure of @var{alist}, |
| 4562 | and so may cause unusual results if passed an object that is not an |
| 4563 | association list. |
| 4564 | @end deffn |
| 4565 | |
| 4566 | @node Retrieving Alist Entries |
| 4567 | @subsubsection Retrieving Alist Entries |
| 4568 | @rnindex assq |
| 4569 | @rnindex assv |
| 4570 | @rnindex assoc |
| 4571 | |
| 4572 | @code{assq}, @code{assv} and @code{assoc} take an alist and a key as |
| 4573 | arguments and return the entry for that key if an entry exists, or |
| 4574 | @code{#f} if there is no entry for that key. Note that, in the cases |
| 4575 | where an entry exists, these procedures return the complete entry, that |
| 4576 | is @code{(KEY . VALUE)}, not just the value. |
| 4577 | |
| 4578 | @deffn primitive assq key alist |
| 4579 | @deffnx primitive assv key alist |
| 4580 | @deffnx primitive assoc key alist |
| 4581 | Fetches the entry in @var{alist} that is associated with @var{key}. To |
| 4582 | decide whether the argument @var{key} matches a particular entry in |
| 4583 | @var{alist}, @code{assq} compares keys with @code{eq?}, @code{assv} |
| 4584 | uses @code{eqv?} and @code{assoc} uses @code{equal?}. If @var{key} |
| 4585 | cannot be found in @var{alist} (according to whichever equality |
| 4586 | predicate is in use), then @code{#f} is returned. These functions |
| 4587 | return the entire alist entry found (i.e. both the key and the value). |
| 4588 | @end deffn |
| 4589 | |
| 4590 | @code{assq-ref}, @code{assv-ref} and @code{assoc-ref}, on the other |
| 4591 | hand, take an alist and a key and return @emph{just the value} for that |
| 4592 | key, if an entry exists. If there is no entry for the specified key, |
| 4593 | these procedures return @code{#f}. |
| 4594 | |
| 4595 | This creates an ambiguity: if the return value is @code{#f}, it means |
| 4596 | either that there is no entry with the specified key, or that there |
| 4597 | @emph{is} an entry for the specified key, with value @code{#f}. |
| 4598 | Consequently, @code{assq-ref} and friends should only be used where it |
| 4599 | is known that an entry exists, or where the ambiguity doesn't matter |
| 4600 | for some other reason. |
| 4601 | |
| 4602 | @deffn primitive assq-ref alist key |
| 4603 | @deffnx primitive assv-ref alist key |
| 4604 | @deffnx primitive assoc-ref alist key |
| 4605 | Like @code{assq}, @code{assv} and @code{assoc}, except that only the |
| 4606 | value associated with @var{key} in @var{alist} is returned. These |
| 4607 | functions are equivalent to |
| 4608 | |
| 4609 | @lisp |
| 4610 | (let ((ent (@var{associator} @var{key} @var{alist}))) |
| 4611 | (and ent (cdr ent))) |
| 4612 | @end lisp |
| 4613 | |
| 4614 | where @var{associator} is one of @code{assq}, @code{assv} or @code{assoc}. |
| 4615 | @end deffn |
| 4616 | |
| 4617 | @node Removing Alist Entries |
| 4618 | @subsubsection Removing Alist Entries |
| 4619 | |
| 4620 | To remove the element from an association list whose key matches a |
| 4621 | specified key, use @code{assq-remove!}, @code{assv-remove!} or |
| 4622 | @code{assoc-remove!} (depending, as usual, on the level of equality |
| 4623 | required between the key that you specify and the keys in the |
| 4624 | association list). |
| 4625 | |
| 4626 | As with @code{assq-set!} and friends, the specified alist may or may not |
| 4627 | be modified destructively, and the only safe way to update a variable |
| 4628 | containing the alist is to @code{set!} it to the value that |
| 4629 | @code{assq-remove!} and friends return. |
| 4630 | |
| 4631 | @example |
| 4632 | address-list |
| 4633 | @result{} |
| 4634 | (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road") |
| 4635 | ("james" . "1a London Road")) |
| 4636 | |
| 4637 | (set! address-list (assoc-remove! address-list "mary")) |
| 4638 | address-list |
| 4639 | @result{} |
| 4640 | (("bob" . "11 Newington Avenue") ("james" . "1a London Road")) |
| 4641 | @end example |
| 4642 | |
| 4643 | Note that, when @code{assq/v/oc-remove!} is used to modify an |
| 4644 | association list that has been constructed only using the corresponding |
| 4645 | @code{assq/v/oc-set!}, there can be at most one matching entry in the |
| 4646 | alist, so the question of multiple entries being removed in one go does |
| 4647 | not arise. If @code{assq/v/oc-remove!} is applied to an association |
| 4648 | list that has been constructed using @code{acons}, or an |
| 4649 | @code{assq/v/oc-set!} with a different level of equality, or any mixture |
| 4650 | of these, it removes only the first matching entry from the alist, even |
| 4651 | if the alist might contain further matching entries. For example: |
| 4652 | |
| 4653 | @example |
| 4654 | (define address-list '()) |
| 4655 | (set! address-list (assq-set! address-list "mary" "11 Elm Street")) |
| 4656 | (set! address-list (assq-set! address-list "mary" "57 Pine Drive")) |
| 4657 | address-list |
| 4658 | @result{} |
| 4659 | (("mary" . "57 Pine Drive") ("mary" . "11 Elm Street")) |
| 4660 | |
| 4661 | (set! address-list (assoc-remove! address-list "mary")) |
| 4662 | address-list |
| 4663 | @result{} |
| 4664 | (("mary" . "11 Elm Street")) |
| 4665 | @end example |
| 4666 | |
| 4667 | In this example, the two instances of the string "mary" are not the same |
| 4668 | when compared using @code{eq?}, so the two @code{assq-set!} calls add |
| 4669 | two distinct entries to @code{address-list}. When compared using |
| 4670 | @code{equal?}, both "mary"s in @code{address-list} are the same as the |
| 4671 | "mary" in the @code{assoc-remove!} call, but @code{assoc-remove!} stops |
| 4672 | after removing the first matching entry that it finds, and so one of the |
| 4673 | "mary" entries is left in place. |
| 4674 | |
| 4675 | @deffn primitive assq-remove! alist key |
| 4676 | @deffnx primitive assv-remove! alist key |
| 4677 | @deffnx primitive assoc-remove! alist key |
| 4678 | Delete the first entry in @var{alist} associated with @var{key}, and return |
| 4679 | the resulting alist. |
| 4680 | @end deffn |
| 4681 | |
| 4682 | @node Sloppy Alist Functions |
| 4683 | @subsubsection Sloppy Alist Functions |
| 4684 | |
| 4685 | @code{sloppy-assq}, @code{sloppy-assv} and @code{sloppy-assoc} behave |
| 4686 | like the corresponding non-@code{sloppy-} procedures, except that they |
| 4687 | return @code{#f} when the specified association list is not well-formed, |
| 4688 | where the non-@code{sloppy-} versions would signal an error. |
| 4689 | |
| 4690 | Specifically, there are two conditions for which the non-@code{sloppy-} |
| 4691 | procedures signal an error, which the @code{sloppy-} procedures handle |
| 4692 | instead by returning @code{#f}. Firstly, if the specified alist as a |
| 4693 | whole is not a proper list: |
| 4694 | |
| 4695 | @example |
| 4696 | (assoc "mary" '((1 . 2) ("key" . "door") . "open sesame")) |
| 4697 | @result{} |
| 4698 | ERROR: In procedure assoc in expression (assoc "mary" (quote #)): |
| 4699 | ERROR: Wrong type argument in position 2 (expecting NULLP): "open sesame" |
| 4700 | ABORT: (wrong-type-arg) |
| 4701 | |
| 4702 | (sloppy-assoc "mary" '((1 . 2) ("key" . "door") . "open sesame")) |
| 4703 | @result{} |
| 4704 | #f |
| 4705 | @end example |
| 4706 | |
| 4707 | @noindent |
| 4708 | Secondly, if one of the entries in the specified alist is not a pair: |
| 4709 | |
| 4710 | @example |
| 4711 | (assoc 2 '((1 . 1) 2 (3 . 9))) |
| 4712 | @result{} |
| 4713 | ERROR: In procedure assoc in expression (assoc 2 (quote #)): |
| 4714 | ERROR: Wrong type argument in position 2 (expecting CONSP): 2 |
| 4715 | ABORT: (wrong-type-arg) |
| 4716 | |
| 4717 | (sloppy-assoc 2 '((1 . 1) 2 (3 . 9))) |
| 4718 | @result{} |
| 4719 | #f |
| 4720 | @end example |
| 4721 | |
| 4722 | Unless you are explicitly working with badly formed association lists, |
| 4723 | it is much safer to use the non-@code{sloppy-} procedures, because they |
| 4724 | help to highlight coding and data errors that the @code{sloppy-} |
| 4725 | versions would silently cover up. |
| 4726 | |
| 4727 | @deffn primitive sloppy-assq key alist |
| 4728 | Behaves like @code{assq} but does not do any error checking. |
| 4729 | Recommended only for use in Guile internals. |
| 4730 | @end deffn |
| 4731 | |
| 4732 | @deffn primitive sloppy-assv key alist |
| 4733 | Behaves like @code{assv} but does not do any error checking. |
| 4734 | Recommended only for use in Guile internals. |
| 4735 | @end deffn |
| 4736 | |
| 4737 | @deffn primitive sloppy-assoc key alist |
| 4738 | Behaves like @code{assoc} but does not do any error checking. |
| 4739 | Recommended only for use in Guile internals. |
| 4740 | @end deffn |
| 4741 | |
| 4742 | @node Alist Example |
| 4743 | @subsubsection Alist Example |
| 4744 | |
| 4745 | Here is a longer example of how alists may be used in practice. |
| 4746 | |
| 4747 | @lisp |
| 4748 | (define capitals '(("New York" . "Albany") |
| 4749 | ("Oregon" . "Salem") |
| 4750 | ("Florida" . "Miami"))) |
| 4751 | |
| 4752 | ;; What's the capital of Oregon? |
| 4753 | (assoc "Oregon" capitals) @result{} ("Oregon" . "Salem") |
| 4754 | (assoc-ref capitals "Oregon") @result{} "Salem" |
| 4755 | |
| 4756 | ;; We left out South Dakota. |
| 4757 | (set! capitals |
| 4758 | (assoc-set! capitals "South Dakota" "Bismarck")) |
| 4759 | capitals |
| 4760 | @result{} (("South Dakota" . "Bismarck") |
| 4761 | ("New York" . "Albany") |
| 4762 | ("Oregon" . "Salem") |
| 4763 | ("Florida" . "Miami")) |
| 4764 | |
| 4765 | ;; And we got Florida wrong. |
| 4766 | (set! capitals |
| 4767 | (assoc-set! capitals "Florida" "Tallahassee")) |
| 4768 | capitals |
| 4769 | @result{} (("South Dakota" . "Bismarck") |
| 4770 | ("New York" . "Albany") |
| 4771 | ("Oregon" . "Salem") |
| 4772 | ("Florida" . "Tallahassee")) |
| 4773 | |
| 4774 | ;; After Oregon secedes, we can remove it. |
| 4775 | (set! capitals |
| 4776 | (assoc-remove! capitals "Oregon")) |
| 4777 | capitals |
| 4778 | @result{} (("South Dakota" . "Bismarck") |
| 4779 | ("New York" . "Albany") |
| 4780 | ("Florida" . "Tallahassee")) |
| 4781 | @end lisp |
| 4782 | |
| 4783 | @node Hash Tables |
| 4784 | @subsection Hash Tables |
| 4785 | @tpindex Hash Tables |
| 4786 | |
| 4787 | Like the association list functions, the hash table functions come |
| 4788 | in several varieties: @code{hashq}, @code{hashv}, and @code{hash}. |
| 4789 | The @code{hashq} functions use @code{eq?} to determine whether two |
| 4790 | keys match. The @code{hashv} functions use @code{eqv?}, and the |
| 4791 | @code{hash} functions use @code{equal?}. |
| 4792 | |
| 4793 | In each of the functions that follow, the @var{table} argument |
| 4794 | must be a vector. The @var{key} and @var{value} arguments may be |
| 4795 | any Scheme object. |
| 4796 | |
| 4797 | @deffn procedure make-hash-table size |
| 4798 | Create a new hash table of @var{size} slots. Note that the number of |
| 4799 | slots does not limit the size of the table, it just tells how large |
| 4800 | the underlying vector will be. The @var{size} should be similar to |
| 4801 | the expected number of elements which will be added to the table, but |
| 4802 | they need not match. For good performance, it might be a good idea to |
| 4803 | use a prime number as the @var{size}. |
| 4804 | @end deffn |
| 4805 | |
| 4806 | @deffn primitive hashq-ref table key [dflt] |
| 4807 | Look up @var{key} in the hash table @var{table}, and return the |
| 4808 | value (if any) associated with it. If @var{key} is not found, |
| 4809 | return @var{default} (or @code{#f} if no @var{default} argument |
| 4810 | is supplied). Uses @code{eq?} for equality testing. |
| 4811 | @end deffn |
| 4812 | |
| 4813 | @deffn primitive hashv-ref table key [dflt] |
| 4814 | Look up @var{key} in the hash table @var{table}, and return the |
| 4815 | value (if any) associated with it. If @var{key} is not found, |
| 4816 | return @var{default} (or @code{#f} if no @var{default} argument |
| 4817 | is supplied). Uses @code{eqv?} for equality testing. |
| 4818 | @end deffn |
| 4819 | |
| 4820 | @deffn primitive hash-ref table key [dflt] |
| 4821 | Look up @var{key} in the hash table @var{table}, and return the |
| 4822 | value (if any) associated with it. If @var{key} is not found, |
| 4823 | return @var{default} (or @code{#f} if no @var{default} argument |
| 4824 | is supplied). Uses @code{equal?} for equality testing. |
| 4825 | @end deffn |
| 4826 | |
| 4827 | @deffn primitive hashq-set! table key val |
| 4828 | Find the entry in @var{table} associated with @var{key}, and |
| 4829 | store @var{value} there. Uses @code{eq?} for equality testing. |
| 4830 | @end deffn |
| 4831 | |
| 4832 | @deffn primitive hashv-set! table key val |
| 4833 | Find the entry in @var{table} associated with @var{key}, and |
| 4834 | store @var{value} there. Uses @code{eqv?} for equality testing. |
| 4835 | @end deffn |
| 4836 | |
| 4837 | @deffn primitive hash-set! table key val |
| 4838 | Find the entry in @var{table} associated with @var{key}, and |
| 4839 | store @var{value} there. Uses @code{equal?} for equality |
| 4840 | testing. |
| 4841 | @end deffn |
| 4842 | |
| 4843 | @deffn primitive hashq-remove! table key |
| 4844 | Remove @var{key} (and any value associated with it) from |
| 4845 | @var{table}. Uses @code{eq?} for equality tests. |
| 4846 | @end deffn |
| 4847 | |
| 4848 | @deffn primitive hashv-remove! table key |
| 4849 | Remove @var{key} (and any value associated with it) from |
| 4850 | @var{table}. Uses @code{eqv?} for equality tests. |
| 4851 | @end deffn |
| 4852 | |
| 4853 | @deffn primitive hash-remove! table key |
| 4854 | Remove @var{key} (and any value associated with it) from |
| 4855 | @var{table}. Uses @code{equal?} for equality tests. |
| 4856 | @end deffn |
| 4857 | |
| 4858 | The standard hash table functions may be too limited for some |
| 4859 | applications. For example, you may want a hash table to store |
| 4860 | strings in a case-insensitive manner, so that references to keys |
| 4861 | named ``foobar'', ``FOOBAR'' and ``FooBaR'' will all yield the |
| 4862 | same item. Guile provides you with @dfn{extended} hash tables |
| 4863 | that permit you to specify a hash function and associator function |
| 4864 | of your choosing. The functions described in the rest of this section |
| 4865 | can be used to implement such custom hash table structures. |
| 4866 | |
| 4867 | If you are unfamiliar with the inner workings of hash tables, then |
| 4868 | this facility will probably be a little too abstract for you to |
| 4869 | use comfortably. If you are interested in learning more, see an |
| 4870 | introductory textbook on data structures or algorithms for an |
| 4871 | explanation of how hash tables are implemented. |
| 4872 | |
| 4873 | @deffn primitive hashq key size |
| 4874 | Determine a hash value for @var{key} that is suitable for |
| 4875 | lookups in a hashtable of size @var{size}, where @code{eq?} is |
| 4876 | used as the equality predicate. The function returns an |
| 4877 | integer in the range 0 to @var{size} - 1. Note that |
| 4878 | @code{hashq} may use internal addresses. Thus two calls to |
| 4879 | hashq where the keys are @code{eq?} are not guaranteed to |
| 4880 | deliver the same value if the key object gets garbage collected |
| 4881 | in between. This can happen, for example with symbols: |
| 4882 | @code{(hashq 'foo n) (gc) (hashq 'foo n)} may produce two |
| 4883 | different values, since @code{foo} will be garbage collected. |
| 4884 | @end deffn |
| 4885 | |
| 4886 | @deffn primitive hashv key size |
| 4887 | Determine a hash value for @var{key} that is suitable for |
| 4888 | lookups in a hashtable of size @var{size}, where @code{eqv?} is |
| 4889 | used as the equality predicate. The function returns an |
| 4890 | integer in the range 0 to @var{size} - 1. Note that |
| 4891 | @code{(hashv key)} may use internal addresses. Thus two calls |
| 4892 | to hashv where the keys are @code{eqv?} are not guaranteed to |
| 4893 | deliver the same value if the key object gets garbage collected |
| 4894 | in between. This can happen, for example with symbols: |
| 4895 | @code{(hashv 'foo n) (gc) (hashv 'foo n)} may produce two |
| 4896 | different values, since @code{foo} will be garbage collected. |
| 4897 | @end deffn |
| 4898 | |
| 4899 | @deffn primitive hash key size |
| 4900 | Determine a hash value for @var{key} that is suitable for |
| 4901 | lookups in a hashtable of size @var{size}, where @code{equal?} |
| 4902 | is used as the equality predicate. The function returns an |
| 4903 | integer in the range 0 to @var{size} - 1. |
| 4904 | @end deffn |
| 4905 | |
| 4906 | @deffn primitive hashx-ref hash assoc table key [dflt] |
| 4907 | This behaves the same way as the corresponding @code{ref} |
| 4908 | function, but uses @var{hash} as a hash function and |
| 4909 | @var{assoc} to compare keys. @code{hash} must be a function |
| 4910 | that takes two arguments, a key to be hashed and a table size. |
| 4911 | @code{assoc} must be an associator function, like @code{assoc}, |
| 4912 | @code{assq} or @code{assv}. |
| 4913 | |
| 4914 | By way of illustration, @code{hashq-ref table key} is |
| 4915 | equivalent to @code{hashx-ref hashq assq table key}. |
| 4916 | @end deffn |
| 4917 | |
| 4918 | @deffn primitive hashx-set! hash assoc table key val |
| 4919 | This behaves the same way as the corresponding @code{set!} |
| 4920 | function, but uses @var{hash} as a hash function and |
| 4921 | @var{assoc} to compare keys. @code{hash} must be a function |
| 4922 | that takes two arguments, a key to be hashed and a table size. |
| 4923 | @code{assoc} must be an associator function, like @code{assoc}, |
| 4924 | @code{assq} or @code{assv}. |
| 4925 | |
| 4926 | By way of illustration, @code{hashq-set! table key} is |
| 4927 | equivalent to @code{hashx-set! hashq assq table key}. |
| 4928 | @end deffn |
| 4929 | |
| 4930 | @deffn primitive hashq-get-handle table key |
| 4931 | This procedure returns the @code{(key . value)} pair from the |
| 4932 | hash table @var{table}. If @var{table} does not hold an |
| 4933 | associated value for @var{key}, @code{#f} is returned. |
| 4934 | Uses @code{eq?} for equality testing. |
| 4935 | @end deffn |
| 4936 | |
| 4937 | @deffn primitive hashv-get-handle table key |
| 4938 | This procedure returns the @code{(key . value)} pair from the |
| 4939 | hash table @var{table}. If @var{table} does not hold an |
| 4940 | associated value for @var{key}, @code{#f} is returned. |
| 4941 | Uses @code{eqv?} for equality testing. |
| 4942 | @end deffn |
| 4943 | |
| 4944 | @deffn primitive hash-get-handle table key |
| 4945 | This procedure returns the @code{(key . value)} pair from the |
| 4946 | hash table @var{table}. If @var{table} does not hold an |
| 4947 | associated value for @var{key}, @code{#f} is returned. |
| 4948 | Uses @code{equal?} for equality testing. |
| 4949 | @end deffn |
| 4950 | |
| 4951 | @deffn primitive hashx-get-handle hash assoc table key |
| 4952 | This behaves the same way as the corresponding |
| 4953 | @code{-get-handle} function, but uses @var{hash} as a hash |
| 4954 | function and @var{assoc} to compare keys. @code{hash} must be |
| 4955 | a function that takes two arguments, a key to be hashed and a |
| 4956 | table size. @code{assoc} must be an associator function, like |
| 4957 | @code{assoc}, @code{assq} or @code{assv}. |
| 4958 | @end deffn |
| 4959 | |
| 4960 | @deffn primitive hashq-create-handle! table key init |
| 4961 | This function looks up @var{key} in @var{table} and returns its handle. |
| 4962 | If @var{key} is not already present, a new handle is created which |
| 4963 | associates @var{key} with @var{init}. |
| 4964 | @end deffn |
| 4965 | |
| 4966 | @deffn primitive hashv-create-handle! table key init |
| 4967 | This function looks up @var{key} in @var{table} and returns its handle. |
| 4968 | If @var{key} is not already present, a new handle is created which |
| 4969 | associates @var{key} with @var{init}. |
| 4970 | @end deffn |
| 4971 | |
| 4972 | @deffn primitive hash-create-handle! table key init |
| 4973 | This function looks up @var{key} in @var{table} and returns its handle. |
| 4974 | If @var{key} is not already present, a new handle is created which |
| 4975 | associates @var{key} with @var{init}. |
| 4976 | @end deffn |
| 4977 | |
| 4978 | @deffn primitive hashx-create-handle! hash assoc table key init |
| 4979 | This behaves the same way as the corresponding |
| 4980 | @code{-create-handle} function, but uses @var{hash} as a hash |
| 4981 | function and @var{assoc} to compare keys. @code{hash} must be |
| 4982 | a function that takes two arguments, a key to be hashed and a |
| 4983 | table size. @code{assoc} must be an associator function, like |
| 4984 | @code{assoc}, @code{assq} or @code{assv}. |
| 4985 | @end deffn |
| 4986 | |
| 4987 | @deffn primitive hash-fold proc init table |
| 4988 | An iterator over hash-table elements. |
| 4989 | Accumulates and returns a result by applying PROC successively. |
| 4990 | The arguments to PROC are "(key value prior-result)" where key |
| 4991 | and value are successive pairs from the hash table TABLE, and |
| 4992 | prior-result is either INIT (for the first application of PROC) |
| 4993 | or the return value of the previous application of PROC. |
| 4994 | For example, @code{(hash-fold acons () tab)} will convert a hash |
| 4995 | table into an a-list of key-value pairs. |
| 4996 | @end deffn |
| 4997 | |
| 4998 | |
| 4999 | @node Hooks |
| 5000 | @section Hooks |
| 5001 | @tpindex Hooks |
| 5002 | |
| 5003 | @c FIXME::martin: Review me! |
| 5004 | |
| 5005 | A hook is basically a list of procedures to be called at well defined |
| 5006 | points in time. Hooks are used internally for several debugging |
| 5007 | facilities, but they can be used in user code, too. |
| 5008 | |
| 5009 | Hooks are created with @code{make-hook}, then procedures can be added to |
| 5010 | a hook with @code{add-hook!} or removed with @code{remove-hook!} or |
| 5011 | @code{reset-hook!}. The procedures stored in a hook can be invoked with |
| 5012 | @code{run-hook}. |
| 5013 | |
| 5014 | @menu |
| 5015 | * Hook Examples:: Hook usage by example. |
| 5016 | * Hook Reference:: Reference of all hook procedures. |
| 5017 | @end menu |
| 5018 | |
| 5019 | @node Hook Examples |
| 5020 | @subsection Hook Examples |
| 5021 | |
| 5022 | Hook usage is shown by some examples in this section. First, we will |
| 5023 | define a hook of arity 2 --- that is, the procedures stored in the hook |
| 5024 | will have to accept two arguments. |
| 5025 | |
| 5026 | @lisp |
| 5027 | (define hook (make-hook 2)) |
| 5028 | hook |
| 5029 | @result{} #<hook 2 40286c90> |
| 5030 | @end lisp |
| 5031 | |
| 5032 | Now we are ready to add some procedures to the newly created hook with |
| 5033 | @code{add-hook!}. In the following example, two procedures are added, |
| 5034 | which print different messages and do different things with their |
| 5035 | arguments. When the procedures have been added, we can invoke them |
| 5036 | using @code{run-hook}. |
| 5037 | |
| 5038 | @lisp |
| 5039 | (add-hook! hook (lambda (x y) |
| 5040 | (display "Foo: ") |
| 5041 | (display (+ x y)) |
| 5042 | (newline))) |
| 5043 | (add-hook! hook (lambda (x y) |
| 5044 | (display "Bar: ") |
| 5045 | (display (* x y)) |
| 5046 | (newline))) |
| 5047 | (run-hook hook 3 4) |
| 5048 | @print{} Bar: 12 |
| 5049 | @print{} Foo: 7 |
| 5050 | @end lisp |
| 5051 | |
| 5052 | Note that the procedures are called in reverse order than they were |
| 5053 | added. This can be changed by providing the optional third argument |
| 5054 | on the second call to @code{add-hook!}. |
| 5055 | |
| 5056 | @lisp |
| 5057 | (add-hook! hook (lambda (x y) |
| 5058 | (display "Foo: ") |
| 5059 | (display (+ x y)) |
| 5060 | (newline))) |
| 5061 | (add-hook! hook (lambda (x y) |
| 5062 | (display "Bar: ") |
| 5063 | (display (* x y)) |
| 5064 | (newline)) |
| 5065 | #t) ; @r{<- Change here!} |
| 5066 | (run-hook hook 3 4) |
| 5067 | @print{} Foo: 7 |
| 5068 | @print{} Bar: 12 |
| 5069 | @end lisp |
| 5070 | |
| 5071 | @node Hook Reference |
| 5072 | @subsection Hook Reference |
| 5073 | |
| 5074 | When a hook is created with @code{make-hook}, you can supply the arity |
| 5075 | of the procedures which can be added to the hook. The arity defaults to |
| 5076 | zero. All procedures of a hook must have the same arity, and when the |
| 5077 | procedures are invoked using @code{run-hook}, the number of arguments |
| 5078 | must match the arity of the procedures. |
| 5079 | |
| 5080 | The order in which procedures are added to a hook matters. If the third |
| 5081 | parameter to @var{add-hook!} is omitted or is equal to @code{#f}, the |
| 5082 | procedure is added in front of the procedures which might already be on |
| 5083 | that hook, otherwise the procedure is added at the end. The procedures |
| 5084 | are always called from first to last when they are invoked via |
| 5085 | @code{run-hook}. |
| 5086 | |
| 5087 | When calling @code{hook->list}, the procedures in the resulting list are |
| 5088 | in the same order as they would have been called by @code{run-hook}. |
| 5089 | |
| 5090 | @deffn primitive make-hook-with-name name [n_args] |
| 5091 | Create a named hook with the name @var{name} for storing |
| 5092 | procedures of arity @var{n_args}. @var{n_args} defaults to |
| 5093 | zero. |
| 5094 | @end deffn |
| 5095 | |
| 5096 | @deffn primitive make-hook [n_args] |
| 5097 | Create a hook for storing procedure of arity |
| 5098 | @var{n_args}. @var{n_args} defaults to zero. |
| 5099 | @end deffn |
| 5100 | |
| 5101 | @deffn primitive hook? x |
| 5102 | Return @code{#t} if @var{x} is a hook, @code{#f} otherwise. |
| 5103 | @end deffn |
| 5104 | |
| 5105 | @deffn primitive hook-empty? hook |
| 5106 | Return @code{#t} if @var{hook} is an empty hook, @code{#f} |
| 5107 | otherwise. |
| 5108 | @end deffn |
| 5109 | |
| 5110 | @deffn primitive add-hook! hook proc [append_p] |
| 5111 | Add the procedure @var{proc} to the hook @var{hook}. The |
| 5112 | procedure is added to the end if @var{append_p} is true, |
| 5113 | otherwise it is added to the front. |
| 5114 | @end deffn |
| 5115 | |
| 5116 | @deffn primitive remove-hook! hook proc |
| 5117 | Remove the procedure @var{proc} from the hook @var{hook}. |
| 5118 | @end deffn |
| 5119 | |
| 5120 | @deffn primitive reset-hook! hook |
| 5121 | Remove all procedures from the hook @var{hook}. |
| 5122 | @end deffn |
| 5123 | |
| 5124 | @deffn primitive run-hook hook . args |
| 5125 | Apply all procedures from the hook @var{hook} to the arguments |
| 5126 | @var{args}. The order of the procedure application is first to |
| 5127 | last. |
| 5128 | @end deffn |
| 5129 | |
| 5130 | @deffn primitive hook->list hook |
| 5131 | Convert the procedure list of @var{hook} to a list. |
| 5132 | @end deffn |
| 5133 | |
| 5134 | |
| 5135 | @node Other Data Types |
| 5136 | @section Other Core Guile Data Types |
| 5137 | |
| 5138 | @c Local Variables: |
| 5139 | @c TeX-master: "guile.texi" |
| 5140 | @c End: |