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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Guile Reference Manual. | |
b8596c08 | 3 | @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2009 |
2da09c3f MV |
4 | @c Free Software Foundation, Inc. |
5 | @c See the file guile.texi for copying conditions. | |
6 | ||
a0e07ba4 NJ |
7 | @page |
8 | @node Pretty Printing | |
3229f68b | 9 | @section Pretty Printing |
a0e07ba4 NJ |
10 | |
11 | @c FIXME::martin: Review me! | |
12 | ||
13 | @cindex pretty printing | |
14 | The module @code{(ice-9 pretty-print)} provides the procedure | |
15 | @code{pretty-print}, which provides nicely formatted output of Scheme | |
16 | objects. This is especially useful for deeply nested or complex data | |
17 | structures, such as lists and vectors. | |
18 | ||
b8596c08 | 19 | The module is loaded by entering the following: |
a0e07ba4 NJ |
20 | |
21 | @lisp | |
22 | (use-modules (ice-9 pretty-print)) | |
23 | @end lisp | |
24 | ||
25 | This makes the procedure @code{pretty-print} available. As an example | |
26 | how @code{pretty-print} will format the output, see the following: | |
27 | ||
28 | @lisp | |
29 | (pretty-print '(define (foo) (lambda (x) | |
385dbc8b KR |
30 | (cond ((zero? x) #t) ((negative? x) -x) (else |
31 | (if (= x 1) 2 (* x x x))))))) | |
a0e07ba4 NJ |
32 | @print{} |
33 | (define (foo) | |
34 | (lambda (x) | |
35 | (cond ((zero? x) #t) | |
36 | ((negative? x) -x) | |
37 | (else (if (= x 1) 2 (* x x x)))))) | |
38 | @end lisp | |
39 | ||
385dbc8b | 40 | @deffn {Scheme Procedure} pretty-print obj [port] [keyword-options] |
a0e07ba4 NJ |
41 | Print the textual representation of the Scheme object @var{obj} to |
42 | @var{port}. @var{port} defaults to the current output port, if not | |
43 | given. | |
385dbc8b KR |
44 | |
45 | The further @var{keyword-options} are keywords and parameters as | |
46 | follows, | |
47 | ||
48 | @table @asis | |
49 | @item @nicode{#:display?} @var{flag} | |
50 | If @var{flag} is true then print using @code{display}. The default is | |
51 | @code{#f} which means use @code{write} style. (@pxref{Writing}) | |
52 | ||
53 | @item @nicode{#:per-line-prefix} @var{string} | |
54 | Print the given @var{string} as a prefix on each line. The default is | |
55 | no prefix. | |
56 | ||
57 | @item @nicode{#:width} @var{columns} | |
58 | Print within the given @var{columns}. The default is 79. | |
59 | @end table | |
a0e07ba4 NJ |
60 | @end deffn |
61 | ||
2a946b44 | 62 | |
b8596c08 AW |
63 | @cindex truncated printing |
64 | Also exported by the @code{(ice-9 pretty-print)} module is | |
65 | @code{truncated-print}, a procedure to print Scheme datums, truncating | |
66 | the output to a certain number of characters. This is useful when you | |
67 | need to present an arbitrary datum to the user, but you only have one | |
68 | line in which to do so. | |
69 | ||
70 | @lisp | |
71 | (define exp '(a b #(c d e) f . g)) | |
72 | (truncated-print exp #:width 10) (newline) | |
73 | @print{} (a b . #) | |
74 | (truncated-print exp #:width 15) (newline) | |
75 | @print{} (a b # f . g) | |
76 | (truncated-print exp #:width 18) (newline) | |
77 | @print{} (a b #(c ...) . #) | |
78 | (truncated-print exp #:width 20) (newline) | |
79 | @print{} (a b #(c d e) f . g) | |
80 | (truncated-print "The quick brown fox" #:width 10) (newline) | |
81 | @print{} "The quick brown..." | |
82 | (truncated-print (current-module) #:width 20) (newline) | |
83 | @print{} #<directory (gui...> | |
84 | @end lisp | |
85 | ||
86 | @code{truncated-print} will not output a trailing newline. If an | |
87 | expression does not fit in the given width, it will be truncated -- | |
88 | possibly ellipsized, or in the worst case, displayed as @nicode{#}. | |
89 | ||
90 | @deffn {Scheme Procedure} truncated-print obj [port] [keyword-options] | |
91 | Print @var{obj}, truncating the output, if necessary, to make it fit | |
92 | into @var{width} characters. By default, @var{x} will be printed using | |
93 | @code{write}, though that behavior can be overriden via the | |
94 | @var{display?} keyword argument. | |
95 | ||
96 | The default behaviour is to print depth-first, meaning that the entire | |
97 | remaining width will be available to each sub-expressoin of @var{x} -- | |
98 | e.g., if @var{x} is a vector, each member of @var{x}. One can attempt to | |
99 | ``ration'' the available width, trying to allocate it equally to each | |
100 | sub-expression, via the @var{breadth-first?} keyword argument. | |
101 | ||
102 | The further @var{keyword-options} are keywords and parameters as | |
103 | follows, | |
104 | ||
105 | @table @asis | |
106 | @item @nicode{#:display?} @var{flag} | |
107 | If @var{flag} is true then print using @code{display}. The default is | |
108 | @code{#f} which means use @code{write} style. (@pxref{Writing}) | |
109 | ||
110 | @item @nicode{#:width} @var{columns} | |
111 | Print within the given @var{columns}. The default is 79. | |
112 | ||
113 | @item @nicode{#:breadth-first?} @var{flag} | |
114 | If @var{flag} is true, then allocate the available width breadth-first | |
115 | among elements of a compound data structure (list, vector, pair, | |
116 | etc.). The default is @code{#f} which means that any element is | |
117 | allowed to consume all of the available width. | |
118 | @end table | |
119 | @end deffn | |
120 | ||
121 | ||
a0e07ba4 NJ |
122 | @page |
123 | @node Formatted Output | |
3229f68b | 124 | @section Formatted Output |
a0e07ba4 | 125 | @cindex formatted output |
a0e07ba4 | 126 | |
76d3f3d4 KR |
127 | @c For reference, in this section escapes like ~a are given in |
128 | @c @nicode, to give code font in TeX etc, but leave them unadorned in | |
129 | @c Info. | |
130 | @c | |
131 | @c The idea is to reduce clutter around what's shown, and avoid any | |
132 | @c possible confusion over whether the ` ' quotes are part of what | |
133 | @c should be entered. (In particular for instance of course ' is | |
134 | @c meaningful in a format string, introducing a char parameter). | |
135 | ||
136 | The @code{format} function is a powerful way to print numbers, strings | |
137 | and other objects together with literal text under the control of a | |
138 | format string. This function is available from | |
139 | ||
140 | @example | |
141 | (use-modules (ice-9 format)) | |
142 | @end example | |
143 | ||
144 | A format string is generally more compact and easier than using just | |
145 | the standard procedures like @code{display}, @code{write} and | |
146 | @code{newline}. Parameters in the output string allow various output | |
147 | styles, and parameters can be taken from the arguments for runtime | |
148 | flexibility. | |
149 | ||
150 | @code{format} is similar to the Common Lisp procedure of the same | |
151 | name, but it's not identical and doesn't have quite all the features | |
152 | found in Common Lisp. | |
153 | ||
154 | C programmers will note the similarity between @code{format} and | |
155 | @code{printf}, though escape sequences are marked with @nicode{~} | |
156 | instead of @nicode{%}, and are more powerful. | |
157 | ||
158 | @sp 1 | |
159 | @deffn {Scheme Procedure} format dest fmt [args@dots{}] | |
160 | Write output specified by the @var{fmt} string to @var{dest}. | |
161 | @var{dest} can be an output port, @code{#t} for | |
162 | @code{current-output-port} (@pxref{Default Ports}), a number for | |
163 | @code{current-error-port}, or @code{#f} to return the output as a | |
164 | string. | |
165 | ||
166 | @var{fmt} can contain literal text to be output, and @nicode{~} | |
167 | escapes. Each escape has the form | |
168 | ||
169 | @example | |
170 | ~ [param [, param@dots{}] [:] [@@] code | |
171 | @end example | |
172 | ||
173 | @nicode{code} is a character determining the escape sequence. The | |
174 | @nicode{:} and @nicode{@@} characters are optional modifiers, one or | |
175 | both of which change the way various codes operate. Optional | |
176 | parameters are accepted by some codes too. Parameters have the | |
177 | following forms, | |
a0e07ba4 | 178 | |
76d3f3d4 | 179 | @table @asis |
80a894c9 | 180 | @item @nicode{[+/-]number} |
76d3f3d4 KR |
181 | An integer, with optional @nicode{+} or @nicode{-}. |
182 | @item @nicode{'} (apostrophe) | |
183 | The following character in the format string, for instance @nicode{'z} | |
184 | for @nicode{z}. | |
185 | @item @nicode{v} | |
186 | The next function argument as the parameter. @nicode{v} stands for | |
187 | ``variable'', a parameter can be calculated at runtime and included in | |
188 | the arguments. Upper case @nicode{V} can be used too. | |
189 | @item @nicode{#} | |
190 | The number of arguments remaining. (See @nicode{~*} below for some | |
191 | usages.) | |
a0e07ba4 NJ |
192 | @end table |
193 | ||
76d3f3d4 KR |
194 | Parameters are separated by commas (@nicode{,}). A parameter can be |
195 | left empty to keep its default value when supplying later parameters. | |
a0e07ba4 | 196 | |
76d3f3d4 KR |
197 | @sp 1 |
198 | The following escapes are available. The code letters are not | |
199 | case-sensitive, upper and lower case are the same. | |
a0e07ba4 | 200 | |
76d3f3d4 KR |
201 | @table @asis |
202 | @item @nicode{~a} | |
203 | @itemx @nicode{~s} | |
204 | Object output. Parameters: @var{minwidth}, @var{padinc}, | |
205 | @var{minpad}, @var{padchar}. | |
206 | ||
207 | @nicode{~a} outputs an argument like @code{display}, @nicode{~s} | |
208 | outputs an argument like @code{write} (@pxref{Writing}). | |
209 | ||
210 | @example | |
211 | (format #t "~a" "foo") @print{} foo | |
212 | (format #t "~s" "foo") @print{} "foo" | |
213 | @end example | |
214 | ||
80a894c9 KR |
215 | @nicode{~:a} and @nicode{~:s} put objects that don't have an external |
216 | representation in quotes like a string. | |
76d3f3d4 KR |
217 | |
218 | @example | |
219 | (format #t "~:a" car) @print{} "#<primitive-procedure car>" | |
220 | @end example | |
221 | ||
222 | If the output is less than @var{minwidth} characters (default 0), it's | |
80a894c9 KR |
223 | padded on the right with @var{padchar} (default space). @nicode{~@@a} |
224 | and @nicode{~@@s} put the padding on the left instead. | |
76d3f3d4 KR |
225 | |
226 | @example | |
227 | (format #f "~5a" 'abc) @result{} "abc " | |
228 | (format #f "~5,,,'-@@a" 'abc) @result{} "--abc" | |
229 | @end example | |
230 | ||
231 | @var{minpad} is a minimum for the padding then plus a multiple of | |
232 | @var{padinc}. Ie.@: the padding is @math{@var{minpad} + @var{N} * | |
233 | @var{padinc}}, where @var{n} is the smallest integer making the total | |
234 | object plus padding greater than or equal to @var{minwidth}. The | |
235 | default @var{minpad} is 0 and the default @var{padinc} is 1 (imposing | |
236 | no minimum or multiple). | |
237 | ||
238 | @example | |
239 | (format #f "~5,1,4a" 'abc) @result{} "abc " | |
240 | @end example | |
241 | ||
242 | @item @nicode{~c} | |
243 | Character. Parameter: @var{charnum}. | |
244 | ||
245 | Output a character. The default is to simply output, as per | |
80a894c9 KR |
246 | @code{write-char} (@pxref{Writing}). @nicode{~@@c} prints in |
247 | @code{write} style. @nicode{~:c} prints control characters (ASCII 0 | |
248 | to 31) in @nicode{^X} form. | |
76d3f3d4 KR |
249 | |
250 | @example | |
251 | (format #t "~c" #\z) @print{} z | |
252 | (format #t "~@@c" #\z) @print{} #\z | |
253 | (format #t "~:c" #\newline) @print{} ^J | |
254 | @end example | |
255 | ||
256 | If the @var{charnum} parameter is given then an argument is not taken | |
257 | but instead the character is @code{(integer->char @var{charnum})} | |
258 | (@pxref{Characters}). This can be used for instance to output | |
259 | characters given by their ASCII code. | |
260 | ||
261 | @example | |
262 | (format #t "~65c") @print{} A | |
263 | @end example | |
264 | ||
265 | @item @nicode{~d} | |
266 | @itemx @nicode{~x} | |
267 | @itemx @nicode{~o} | |
268 | @itemx @nicode{~b} | |
269 | Integer. Parameters: @var{minwidth}, @var{padchar}, @var{commachar}, | |
270 | @var{commawidth}. | |
271 | ||
272 | Output an integer argument as a decimal, hexadecimal, octal or binary | |
273 | integer (respectively). | |
274 | ||
275 | @example | |
276 | (format #t "~d" 123) @print{} 123 | |
277 | @end example | |
278 | ||
80a894c9 | 279 | @nicode{~@@d} etc shows a @nicode{+} sign is shown on positive |
76d3f3d4 KR |
280 | numbers. |
281 | ||
282 | @c FIXME: "+" is not shown on zero, unlike in Common Lisp. Should | |
283 | @c that be changed in the code, or is it too late and should just be | |
284 | @c documented that way? | |
285 | ||
286 | @example | |
287 | (format #t "~@@b" 12) @print{} +1100 | |
288 | @end example | |
289 | ||
290 | If the output is less than the @var{minwidth} parameter (default no | |
291 | minimum), it's padded on the left with the @var{padchar} parameter | |
292 | (default space). | |
293 | ||
294 | @example | |
295 | (format #t "~5,'*d" 12) @print{} ***12 | |
296 | (format #t "~5,'0d" 12) @print{} 00012 | |
297 | (format #t "~3d" 1234) @print{} 1234 | |
298 | @end example | |
299 | ||
80a894c9 KR |
300 | @nicode{~:d} adds commas (or the @var{commachar} parameter) every |
301 | three digits (or the @var{commawidth} parameter many). | |
76d3f3d4 KR |
302 | |
303 | @example | |
304 | (format #t "~:d" 1234567) @print{} 1,234,567 | |
305 | (format #t "~10,'*,'/,2:d" 12345) @print{} ***1/23/45 | |
306 | @end example | |
307 | ||
308 | Hexadecimal @nicode{~x} output is in lower case, but the @nicode{~(} | |
309 | and @nicode{~)} case conversion directives described below can be used | |
310 | to get upper case. | |
311 | ||
312 | @example | |
313 | (format #t "~x" 65261) @print{} feed | |
314 | (format #t "~:@@(~x~)" 65261) @print{} FEED | |
315 | @end example | |
316 | ||
317 | @item @nicode{~r} | |
318 | Integer in words, roman numerals, or a specified radix. Parameters: | |
319 | @var{radix}, @var{minwidth}, @var{padchar}, @var{commachar}, | |
320 | @var{commawidth}. | |
321 | ||
322 | With no parameters output is in words as a cardinal like ``ten'', or | |
80a894c9 | 323 | @nicode{~:r} prints an ordinal like ``tenth''. |
76d3f3d4 KR |
324 | |
325 | @example | |
326 | (format #t "~r" 9) @print{} nine ;; cardinal | |
327 | (format #t "~r" -9) @print{} minus nine ;; cardinal | |
328 | (format #t "~:r" 9) @print{} ninth ;; ordinal | |
329 | @end example | |
330 | ||
80a894c9 | 331 | And also with no parameters, @nicode{~@@r} gives roman numerals and |
40296bab | 332 | @nicode{~:@@r} gives old roman numerals. In old roman numerals |
80a894c9 KR |
333 | there's no ``subtraction'', so 9 is @nicode{VIIII} instead of |
334 | @nicode{IX}. In both cases only positive numbers can be output. | |
76d3f3d4 KR |
335 | |
336 | @example | |
337 | (format #t "~@@r" 89) @print{} LXXXIX ;; roman | |
40296bab | 338 | (format #t "~:@@r" 89) @print{} LXXXVIIII ;; old roman |
76d3f3d4 KR |
339 | @end example |
340 | ||
341 | When a parameter is given it means numeric output in the specified | |
342 | @var{radix}. The modifiers and parameters following the radix are the | |
343 | same as described for @nicode{~d} etc above. | |
344 | ||
345 | @example | |
346 | (format #f "~3r" 27) @result{} "1000" ;; base 3 | |
347 | (format #f "~3,5r" 26) @result{} " 222" ;; base 3 width 5 | |
348 | @end example | |
349 | ||
350 | @item @nicode{~f} | |
351 | Fixed-point float. Parameters: @var{width}, @var{decimals}, | |
352 | @var{scale}, @var{overflowchar}, @var{padchar}. | |
353 | ||
354 | Output a number or number string in fixed-point format, ie.@: with a | |
355 | decimal point. | |
356 | ||
357 | @example | |
358 | (format #t "~f" 5) @print{} 5.0 | |
359 | (format #t "~f" "123") @print{} 123.0 | |
360 | (format #t "~f" "1e-1") @print{} 0.1 | |
361 | @end example | |
362 | ||
80a894c9 KR |
363 | @nicode{~@@f} prints a @nicode{+} sign on positive numbers (including |
364 | zero). | |
76d3f3d4 KR |
365 | |
366 | @example | |
367 | (format #t "~@@f" 0) @print{} +0.0 | |
368 | @end example | |
369 | ||
370 | If the output is less than @var{width} characters it's padded on the | |
371 | left with @var{padchar} (space by default). If the output equals or | |
372 | exceeds @var{width} then there's no padding. The default for | |
373 | @var{width} is no padding. | |
374 | ||
375 | @example | |
376 | (format #f "~6f" -1.5) @result{} " -1.5" | |
377 | (format #f "~6,,,,'*f" 23) @result{} "**23.0" | |
378 | (format #f "~6f" 1234567.0) @result{} "1234567.0" | |
379 | @end example | |
380 | ||
381 | @var{decimals} is how many digits to print after the decimal point, | |
382 | with the value rounded or padded with zeros as necessary. (The | |
383 | default is to output as many decimals as required.) | |
384 | ||
385 | @example | |
386 | (format #t "~1,2f" 3.125) @print{} 3.13 | |
387 | (format #t "~1,2f" 1.5) @print{} 1.50 | |
388 | @end example | |
389 | ||
390 | @var{scale} is a power of 10 applied to the value, moving the decimal | |
391 | point that many places. A positive @var{scale} increases the value | |
392 | shown, a negative decreases it. | |
393 | ||
394 | @example | |
395 | (format #t "~,,2f" 1234) @print{} 123400.0 | |
396 | (format #t "~,,-2f" 1234) @print{} 12.34 | |
397 | @end example | |
398 | ||
399 | If @var{overflowchar} and @var{width} are both given and if the output | |
400 | would exceed @var{width}, then that many @var{overflowchar}s are | |
401 | printed instead of the value. | |
402 | ||
403 | @example | |
404 | (format #t "~5,,,'xf" 12345) @print{} 12345 | |
405 | (format #t "~4,,,'xf" 12345) @print{} xxxx | |
406 | @end example | |
407 | ||
408 | @item @nicode{~e} | |
409 | Exponential float. Parameters: @var{width}, @var{mantdigits}, | |
410 | @var{expdigits}, @var{intdigits}, @var{overflowchar}, @var{padchar}, | |
411 | @var{expchar}. | |
412 | ||
413 | Output a number or number string in exponential notation. | |
414 | ||
415 | @example | |
416 | (format #t "~e" 5000.25) @print{} 5.00025E+3 | |
417 | (format #t "~e" "123.4") @print{} 1.234E+2 | |
418 | (format #t "~e" "1e4") @print{} 1.0E+4 | |
419 | @end example | |
420 | ||
80a894c9 KR |
421 | @nicode{~@@e} prints a @nicode{+} sign on positive numbers (including |
422 | zero). (This is for the mantissa, a @nicode{+} or @nicode{-} sign is | |
423 | always shown on the exponent.) | |
76d3f3d4 KR |
424 | |
425 | @example | |
426 | (format #t "~@@e" 5000.0) @print{} +5.0E+3 | |
427 | @end example | |
428 | ||
429 | If the output is less than @var{width} characters it's padded on the | |
430 | left with @var{padchar} (space by default). The default for | |
431 | @var{width} is to output with no padding. | |
432 | ||
433 | @example | |
434 | (format #f "~10e" 1234.0) @result{} " 1.234E+3" | |
435 | (format #f "~10,,,,,'*e" 0.5) @result{} "****5.0E-1" | |
436 | @end example | |
437 | ||
438 | @c FIXME: Describe what happens when the number is bigger than WIDTH. | |
439 | @c There seems to be a bit of dodginess about this, or some deviation | |
440 | @c from Common Lisp. | |
441 | ||
442 | @var{mantdigits} is the number of digits shown in the mantissa after | |
443 | the decimal point. The value is rounded or trailing zeros are added | |
444 | as necessary. The default @var{mantdigits} is to show as much as | |
445 | needed by the value. | |
446 | ||
447 | @example | |
448 | (format #f "~,3e" 11111.0) @result{} "1.111E+4" | |
449 | (format #f "~,8e" 123.0) @result{} "1.23000000E+2" | |
450 | @end example | |
451 | ||
452 | @var{expdigits} is the minimum number of digits shown for the | |
453 | exponent, with leading zeros added if necessary. The default for | |
454 | @var{expdigits} is to show only as many digits as required. At least | |
455 | 1 digit is always shown. | |
456 | ||
457 | @example | |
458 | (format #f "~,,1e" 1.0e99) @result{} "1.0E+99" | |
459 | (format #f "~,,6e" 1.0e99) @result{} "1.0E+000099" | |
460 | @end example | |
461 | ||
462 | @var{intdigits} (default 1) is the number of digits to show before the | |
463 | decimal point in the mantissa. @var{intdigits} can be zero, in which | |
464 | case the integer part is a single @nicode{0}, or it can be negative, | |
465 | in which case leading zeros are shown after the decimal point. | |
466 | ||
467 | @c FIXME: When INTDIGITS is 0, Common Lisp format apparently only | |
468 | @c shows the single 0 digit if it fits in WIDTH. format.scm seems to | |
469 | @c show it always. Is it meant to? | |
470 | ||
471 | @example | |
472 | (format #t "~,,,3e" 12345.0) @print{} 123.45E+2 | |
473 | (format #t "~,,,0e" 12345.0) @print{} 0.12345E+5 | |
474 | (format #t "~,,,-3e" 12345.0) @print{} 0.00012345E+8 | |
475 | @end example | |
476 | ||
477 | @c FIXME: MANTDIGITS with negative INTDIGITS doesn't match CL spec, | |
478 | @c believe the spec says it ought to still show mantdigits+1 sig | |
479 | @c figures, ie. leading zeros don't count towards MANTDIGITS, but it | |
480 | @c seems to just treat MANTDIGITS as how many digits after the | |
481 | @c decimal point. | |
482 | ||
483 | If @var{overflowchar} is given then @var{width} is a hard limit. If | |
484 | the output would exceed @var{width} then instead that many | |
485 | @var{overflowchar}s are printed. | |
486 | ||
487 | @example | |
488 | (format #f "~6,,,,'xe" 100.0) @result{} "1.0E+2" | |
489 | (format #f "~3,,,,'xe" 100.0) @result{} "xxx" | |
490 | @end example | |
491 | ||
492 | @var{expchar} is the exponent marker character (default @nicode{E}). | |
493 | ||
494 | @example | |
495 | (format #t "~,,,,,,'ee" 100.0) @print{} 1.0e+2 | |
496 | @end example | |
497 | ||
498 | @item @nicode{~g} | |
499 | General float. Parameters: @var{width}, @var{mantdigits}, | |
500 | @var{expdigits}, @var{intdigits}, @var{overflowchar}, @var{padchar}, | |
501 | @var{expchar}. | |
502 | ||
503 | Output a number or number string in either exponential format the same | |
504 | as @nicode{~e}, or fixed-point format like @nicode{~f} but aligned | |
505 | where the mantissa would have been and followed by padding where the | |
506 | exponent would have been. | |
507 | ||
508 | @c FIXME: The default MANTDIGITS is apparently max(needed,min(n,7)) | |
509 | @c where 10^(n-1)<=abs(x)<=10^n. But the Common Lisp spec seems to | |
510 | @c ask for "needed" to be without leading or trailing zeros, whereas | |
511 | @c format.scm seems to include trailing zeros, ending up with it | |
512 | @c using fixed format for bigger values than it should. | |
513 | ||
514 | Fixed-point is used when the absolute value is 0.1 or more and it | |
515 | takes no more space than the mantissa in exponential format, ie.@: | |
516 | basically up to @var{mantdigits} digits. | |
517 | ||
518 | @example | |
519 | (format #f "~12,4,2g" 999.0) @result{} " 999.0 " | |
520 | (format #f "~12,4,2g" "100000") @result{} " 1.0000E+05" | |
521 | @end example | |
522 | ||
523 | The parameters are interpreted as per @nicode{~e} above. When | |
524 | fixed-point is used, the @var{decimals} parameter to @nicode{~f} is | |
525 | established from @var{mantdigits}, so as to give a total | |
526 | @math{@var{mantdigits}+1} figures. | |
527 | ||
528 | @item @nicode{~$} | |
529 | Monetary style fixed-point float. Parameters: @var{decimals}, | |
530 | @var{intdigits}, @var{width}, @var{padchar}. | |
531 | ||
532 | @c For reference, fmtdoc.txi from past versions of slib showed the | |
533 | @c INTDIGITS parameter as SCALE. That looks like a typo, in the code | |
534 | @c and in the Common Lisp spec it's a minimum digits for the integer | |
535 | @c part, it isn't a power of 10 like in ~f. | |
536 | ||
537 | Output a number or number string in fixed-point format, ie.@: with a | |
538 | decimal point. @var{decimals} is the number of decimal places to | |
539 | show, default 2. | |
540 | ||
541 | @example | |
542 | (format #t "~$" 5) @print{} 5.00 | |
543 | (format #t "~4$" "2.25") @print{} 2.2500 | |
544 | (format #t "~4$" "1e-2") @print{} 0.0100 | |
545 | @end example | |
546 | ||
80a894c9 KR |
547 | @nicode{~@@$} prints a @nicode{+} sign on positive numbers (including |
548 | zero). | |
76d3f3d4 KR |
549 | |
550 | @example | |
551 | (format #t "~@@$" 0) @print{} +0.00 | |
552 | @end example | |
553 | ||
554 | @var{intdigits} is a minimum number of digits to show in the integer | |
555 | part of the value (default 1). | |
556 | ||
557 | @example | |
558 | (format #t "~,3$" 9.5) @print{} 009.50 | |
559 | (format #t "~,0$" 0.125) @print{} .13 | |
560 | @end example | |
561 | ||
562 | If the output is less than @var{width} characters (default 0), it's | |
80a894c9 KR |
563 | padded on the left with @var{padchar} (default space). @nicode{~:$} |
564 | puts the padding after the sign. | |
76d3f3d4 KR |
565 | |
566 | @example | |
567 | (format #f "~,,8$" -1.5) @result{} " -1.50" | |
568 | (format #f "~,,8:$" -1.5) @result{} "- 1.50" | |
40296bab | 569 | (format #f "~,,8,'.:@@$" 3) @result{} "+...3.00" |
76d3f3d4 KR |
570 | @end example |
571 | ||
572 | Note that floating point for dollar amounts is generally not a good | |
573 | idea, because a cent @math{0.01} cannot be represented exactly in the | |
574 | binary floating point Guile uses, which leads to slowly accumulating | |
575 | rounding errors. Keeping values as cents (or fractions of a cent) in | |
576 | integers then printing with the scale option in @nicode{~f} may be a | |
577 | better approach. | |
578 | ||
579 | @c For reference, fractions don't work with ~$ (or any of the float | |
580 | @c conversions) currently. If they did work then we could perhaps | |
581 | @c suggest keeping dollar amounts as rationals, which would of course | |
582 | @c give exact cents. An integer as cents is probably still a better | |
583 | @c recommendation though, since it forces one to think about where | |
584 | @c and when rounding can or should occur. | |
585 | ||
586 | @item @nicode{~i} | |
587 | Complex fixed-point float. Parameters: @var{width}, @var{decimals}, | |
588 | @var{scale}, @var{overflowchar}, @var{padchar}. | |
589 | ||
590 | @c For reference, in Common Lisp ~i is an indent, but slib fmtdoc.txi | |
591 | @c described it as complex number output, so we keep that. | |
592 | ||
593 | Output the argument as a complex number, with both real and imaginary | |
594 | part shown (even if one or both are zero). | |
595 | ||
596 | The parameters and modifiers are the same as for fixed-point | |
597 | @nicode{~f} described above. The real and imaginary parts are both | |
598 | output with the same given parameters and modifiers, except that for | |
599 | the imaginary part the @nicode{@@} modifier is always enabled, so as | |
600 | to print a @nicode{+} sign between the real and imaginary parts. | |
601 | ||
602 | @example | |
603 | (format #t "~i" 1) @print{} 1.0+0.0i | |
604 | @end example | |
605 | ||
606 | @item @nicode{~p} | |
607 | Plural. No parameters. | |
608 | ||
609 | Output nothing if the argument is 1, or @samp{s} for any other | |
610 | value. | |
611 | ||
612 | @example | |
613 | (format #t "enter name~p" 1) @print{} enter name | |
614 | (format #t "enter name~p" 2) @print{} enter names | |
615 | @end example | |
616 | ||
80a894c9 | 617 | @nicode{~@@p} prints @samp{y} for 1 or @samp{ies} otherwise. |
76d3f3d4 KR |
618 | |
619 | @example | |
620 | (format #t "pupp~@@p" 1) @print{} puppy | |
621 | (format #t "pupp~@@p" 2) @print{} puppies | |
622 | @end example | |
623 | ||
80a894c9 KR |
624 | @nicode{~:p} re-uses the preceding argument instead of taking a new |
625 | one, which can be convenient when printing some sort of count. | |
76d3f3d4 KR |
626 | |
627 | @example | |
80a894c9 | 628 | (format #t "~d cat~:p" 9) @print{} 9 cats |
40296bab | 629 | (format #t "~d pupp~:@@p" 5) @print{} 5 puppies |
76d3f3d4 KR |
630 | @end example |
631 | ||
80a894c9 KR |
632 | @nicode{~p} is designed for English plurals and there's no attempt to |
633 | support other languages. @nicode{~[} conditionals (below) may be able | |
634 | to help. When using @code{gettext} to translate messages | |
635 | @code{ngettext} is probably best though | |
636 | (@pxref{Internationalization}). | |
637 | ||
76d3f3d4 | 638 | @item @nicode{~y} |
b8596c08 AW |
639 | Structured printing. Parameters: @var{width}. |
640 | ||
641 | @nicode{~y} outputs an argument using @code{pretty-print} | |
642 | (@pxref{Pretty Printing}). The result will be formatted to fit within | |
643 | @var{width} columns (79 by default), consuming multiple lines if | |
644 | necessary. | |
76d3f3d4 | 645 | |
b8596c08 AW |
646 | @nicode{~@@y} outputs an argument using @code{truncated-print} |
647 | (@pxref{Pretty Printing}). The resulting code will be formatted to fit | |
648 | within @var{width} columns (79 by default), on a single line. The | |
649 | output will be truncated if necessary. | |
76d3f3d4 | 650 | |
9274c3dd AW |
651 | @nicode{~:@@y} is like @nicode{~@@y}, except the @var{width} parameter |
652 | is interpreted to be the maximum column to which to output. That is to | |
653 | say, if you are at column 10, and @nicode{~60:@@y} is seen, the datum | |
654 | will be truncated to 50 columns. | |
655 | ||
76d3f3d4 KR |
656 | @item @nicode{~?} |
657 | @itemx @nicode{~k} | |
658 | Sub-format. No parameters. | |
659 | ||
660 | Take a format string argument and a second argument which is a list of | |
80a894c9 KR |
661 | arguments for that string, and output the result. |
662 | ||
663 | @example | |
664 | (format #t "~?" "~d ~d" '(1 2)) @print{} 1 2 | |
665 | @end example | |
666 | ||
667 | @nicode{~@@?} takes arguments for the sub-format directly rather than | |
668 | in a list. | |
76d3f3d4 KR |
669 | |
670 | @example | |
76d3f3d4 KR |
671 | (format #t "~@@? ~s" "~d ~d" 1 2 "foo") @print{} 1 2 "foo" |
672 | @end example | |
673 | ||
674 | @nicode{~?} and @nicode{~k} are the same, @nicode{~k} is provided for | |
675 | T-Scheme compatibility. | |
676 | ||
677 | @item @nicode{~*} | |
678 | Argument jumping. Parameter: @var{N}. | |
679 | ||
80a894c9 KR |
680 | Move forward @var{N} arguments (default 1) in the argument list. |
681 | @nicode{~:*} moves backwards. (@var{N} cannot be negative.) | |
a0e07ba4 | 682 | |
76d3f3d4 | 683 | @example |
471d2c6d KR |
684 | (format #f "~d ~2*~d" 1 2 3 4) @result{} "1 4" |
685 | (format #f "~d ~:*~d" 6) @result{} "6 6" | |
76d3f3d4 | 686 | @end example |
a0e07ba4 | 687 | |
80a894c9 KR |
688 | @nicode{~@@*} moves to argument number @var{N}. The first argument is |
689 | number 0 (and that's the default for @var{N}). | |
a0e07ba4 | 690 | |
76d3f3d4 KR |
691 | @example |
692 | (format #f "~d~d again ~@@*~d~d" 1 2) @result{} "12 again 12" | |
693 | (format #f "~d~d~d ~1@@*~d~d" 1 2 3) @result{} "123 23" | |
694 | @end example | |
a0e07ba4 | 695 | |
471d2c6d KR |
696 | A @nicode{#} move to the end followed by a @nicode{:} modifier move |
697 | back can be used for an absolute position relative to the end of the | |
698 | argument list, a reverse of what the @nicode{@@} modifier does. | |
a0e07ba4 | 699 | |
76d3f3d4 | 700 | @example |
471d2c6d | 701 | (format #t "~#*~2:*~a" 'a 'b 'c 'd) @print{} c |
76d3f3d4 | 702 | @end example |
a0e07ba4 | 703 | |
72b3aa56 | 704 | At the end of the format string the current argument position doesn't |
471d2c6d | 705 | matter, any further arguments are ignored. |
a0e07ba4 | 706 | |
76d3f3d4 KR |
707 | @item @nicode{~t} |
708 | Advance to a column position. Parameters: @var{colnum}, @var{colinc}, | |
709 | @var{padchar}. | |
a0e07ba4 | 710 | |
76d3f3d4 KR |
711 | Output @var{padchar} (space by default) to move to the given |
712 | @var{colnum} column. The start of the line is column 0, the default | |
713 | for @var{colnum} is 1. | |
a0e07ba4 | 714 | |
76d3f3d4 KR |
715 | @example |
716 | (format #f "~tX") @result{} " X" | |
717 | (format #f "~3tX") @result{} " X" | |
718 | @end example | |
a0e07ba4 | 719 | |
76d3f3d4 KR |
720 | If the current column is already past @var{colnum}, then the move is |
721 | to there plus a multiple of @var{colinc}, ie.@: column | |
722 | @math{@var{colnum} + @var{N} * @var{colinc}} for the smallest @var{N} | |
723 | which makes that value greater than or equal to the current column. | |
724 | The default @var{colinc} is 1 (which means no further move). | |
a0e07ba4 | 725 | |
76d3f3d4 KR |
726 | @example |
727 | (format #f "abcd~2,5,'.tx") @result{} "abcd...x" | |
728 | @end example | |
a0e07ba4 | 729 | |
80a894c9 KR |
730 | @nicode{~@@t} takes @var{colnum} as an offset from the current column. |
731 | @var{colnum} many pad characters are output, then further padding to | |
732 | make the current column a multiple of @var{colinc}, if it isn't | |
733 | already so. | |
76d3f3d4 KR |
734 | |
735 | @example | |
736 | (format #f "a~3,5'*@@tx") @result{} "a****x" | |
737 | @end example | |
738 | ||
471d2c6d KR |
739 | @nicode{~t} is implemented using @code{port-column} (@pxref{Reading}), |
740 | so it works even there has been other output before @code{format}. | |
741 | ||
76d3f3d4 KR |
742 | @item @nicode{~~} |
743 | Tilde character. Parameter: @var{n}. | |
744 | ||
745 | Output a tilde character @nicode{~}, or @var{n} many if a parameter is | |
746 | given. Normally @nicode{~} introduces an escape sequence, @nicode{~~} | |
747 | is the way to output a literal tilde. | |
748 | ||
749 | @item @nicode{~%} | |
750 | Newline. Parameter: @var{n}. | |
751 | ||
752 | Output a newline character, or @var{n} many if a parameter is given. | |
753 | A newline (or a few newlines) can of course be output just by | |
754 | including them in the format string. | |
755 | ||
756 | @item @nicode{~&} | |
757 | Start a new line. Parameter: @var{n}. | |
758 | ||
759 | Output a newline if not already at the start of a line. With a | |
760 | parameter, output that many newlines, but with the first only if not | |
761 | already at the start of a line. So for instance 3 would be a newline | |
762 | if not already at the start of a line, and 2 further newlines. | |
763 | ||
764 | @item @nicode{~_} | |
765 | Space character. Parameter: @var{n}. | |
766 | ||
767 | @c For reference, in Common Lisp ~_ is a conditional newline, but | |
768 | @c slib fmtdoc.txi described it as a space, so we keep that. | |
769 | ||
770 | Output a space character, or @var{n} many if a parameter is given. | |
771 | ||
772 | With a variable parameter this is one way to insert runtime calculated | |
773 | padding (@nicode{~t} or the various field widths can do similar | |
774 | things). | |
775 | ||
776 | @example | |
777 | (format #f "~v_foo" 4) @result{} " foo" | |
778 | @end example | |
779 | ||
780 | @item @nicode{~/} | |
781 | Tab character. Parameter: @var{n}. | |
782 | ||
783 | Output a tab character, or @var{n} many if a parameter is given. | |
784 | ||
785 | @item @nicode{~|} | |
786 | Formfeed character. Parameter: @var{n}. | |
787 | ||
788 | Output a formfeed character, or @var{n} many if a parameter is given. | |
789 | ||
790 | @item @nicode{~!} | |
791 | Force output. No parameters. | |
792 | ||
793 | At the end of output, call @code{force-output} to flush any buffers on | |
794 | the destination (@pxref{Writing}). @nicode{~!} can occur anywhere in | |
795 | the format string, but the force is done at the end of output. | |
796 | ||
797 | When output is to a string (destination @code{#f}), @nicode{~!} does | |
798 | nothing. | |
799 | ||
800 | @item @nicode{~newline} (ie.@: newline character) | |
801 | Continuation line. No parameters. | |
802 | ||
803 | Skip this newline and any following whitespace in the format string, | |
80a894c9 KR |
804 | ie.@: don't send it to the output. This can be used to break up a |
805 | long format string for readability, but not print the extra | |
76d3f3d4 KR |
806 | whitespace. |
807 | ||
76d3f3d4 KR |
808 | @example |
809 | (format #f "abc~ | |
810 | ~d def~ | |
811 | ~d" 1 2) @result{} "abc1 def2" | |
812 | @end example | |
813 | ||
80a894c9 KR |
814 | @nicode{~:newline} skips the newline but leaves any further whitespace |
815 | to be printed normally. | |
816 | ||
817 | @nicode{~@@newline} prints the newline then skips following | |
818 | whitespace. | |
819 | ||
76d3f3d4 | 820 | @item @nicode{~(} @nicode{~)} |
f0a9ab4d KR |
821 | Case conversion. No parameters. |
822 | ||
823 | Between @nicode{~(} and @nicode{~)} the case of all output is changed. | |
824 | The modifiers on @nicode{~(} control the conversion. | |
76d3f3d4 | 825 | |
f47029a1 | 826 | @itemize @w{} |
76d3f3d4 | 827 | @item |
80a894c9 | 828 | @nicode{~(} --- lower case. |
76d3f3d4 KR |
829 | @c |
830 | @c FIXME: The : and @ modifiers are not yet documented because the | |
831 | @c code applies string-capitalize and string-capitalize-first to each | |
832 | @c separate format:out-str call, which has various subtly doubtful | |
833 | @c effects. And worse they're applied to individual characters, | |
834 | @c including literal characters in the format string, which has the | |
835 | @c silly effect of being always an upcase. | |
836 | @c | |
837 | @c The Common Lisp spec is apparently for the capitalization to be | |
838 | @c applied in one hit to the whole of the output between ~( and ~). | |
839 | @c (This can no doubt be implemented without accumulating all that | |
840 | @c text, just by keeping a state or the previous char to tell whether | |
841 | @c within a word.) | |
842 | @c | |
843 | @c @item | |
844 | @c @nicode{:} --- first letter of each word upper case, the rest lower | |
845 | @c case, as per the @code{string-capitalize} function (@pxref{Alphabetic | |
846 | @c Case Mapping}). | |
847 | @c @item | |
848 | @c @nicode{@@} --- first letter of just the first word upper case, the | |
849 | @c rest lower case. | |
850 | @c | |
851 | @item | |
40296bab | 852 | @nicode{~:@@(} --- upper case. |
76d3f3d4 KR |
853 | @end itemize |
854 | ||
855 | For example, | |
856 | ||
857 | @example | |
858 | (format #t "~(Hello~)") @print{} hello | |
40296bab | 859 | (format #t "~:@@(Hello~)") @print{} HELLO |
76d3f3d4 KR |
860 | @end example |
861 | ||
862 | In the future it's intended the modifiers @nicode{:} and @nicode{@@} | |
863 | alone will capitalize the first letters of words, as per Common Lisp | |
864 | @code{format}, but the current implementation of this is flawed and | |
865 | not recommended for use. | |
866 | ||
867 | Case conversions do not nest, currently. This might change in the | |
868 | future, but if it does then it will be to Common Lisp style where the | |
869 | outermost conversion has priority, overriding inner ones (making those | |
870 | fairly pointless). | |
871 | ||
872 | @item @nicode{~@{} @nicode{~@}} | |
873 | Iteration. Parameter: @var{maxreps} (for @nicode{~@{}). | |
874 | ||
875 | The format between @nicode{~@{} and @nicode{~@}} is iterated. The | |
876 | modifiers to @nicode{~@{} determine how arguments are taken. The | |
877 | default is a list argument with each iteration successively consuming | |
878 | elements from it. This is a convenient way to output a whole list. | |
879 | ||
880 | @example | |
881 | (format #t "~@{~d~@}" '(1 2 3)) @print{} 123 | |
882 | (format #t "~@{~s=~d ~@}" '("x" 1 "y" 2)) @print{} "x"=1 "y"=2 | |
883 | @end example | |
884 | ||
80a894c9 KR |
885 | @nicode{~:@{} takes a single argument which is a list of lists, each |
886 | of those contained lists gives the arguments for the iterated format. | |
76d3f3d4 | 887 | |
40296bab | 888 | @c @print{} on a new line here to avoid overflowing page width in DVI |
76d3f3d4 | 889 | @example |
40296bab KR |
890 | (format #t "~:@{~dx~d ~@}" '((1 2) (3 4) (5 6))) |
891 | @print{} 1x2 3x4 5x6 | |
76d3f3d4 KR |
892 | @end example |
893 | ||
80a894c9 KR |
894 | @nicode{~@@@{} takes arguments directly, with each iteration |
895 | successively consuming arguments. | |
76d3f3d4 KR |
896 | |
897 | @example | |
898 | (format #t "~@@@{~d~@}" 1 2 3) @print{} 123 | |
899 | (format #t "~@@@{~s=~d ~@}" "x" 1 "y" 2) @print{} "x"=1 "y"=2 | |
900 | @end example | |
901 | ||
40296bab | 902 | @nicode{~:@@@{} takes list arguments, one argument for each iteration, |
80a894c9 | 903 | using that list for the format. |
76d3f3d4 | 904 | |
40296bab | 905 | @c @print{} on a new line here to avoid overflowing page width in DVI |
76d3f3d4 | 906 | @example |
40296bab KR |
907 | (format #t "~:@@@{~dx~d ~@}" '(1 2) '(3 4) '(5 6)) |
908 | @print{} 1x2 3x4 5x6 | |
76d3f3d4 KR |
909 | @end example |
910 | ||
911 | Iterating stops when there are no more arguments or when the | |
912 | @var{maxreps} parameter to @nicode{~@{} is reached (default no | |
913 | maximum). | |
914 | ||
915 | @example | |
916 | (format #t "~2@{~d~@}" '(1 2 3 4)) @print{} 12 | |
917 | @end example | |
918 | ||
919 | If the format between @nicode{~@{} and @nicode{~@}} is empty, then a | |
920 | format string argument is taken (before iteration argument(s)) and | |
921 | used instead. This allows a sub-format (like @nicode{~?} above) to be | |
922 | iterated. | |
923 | ||
924 | @example | |
925 | (format #t "~@{~@}" "~d" '(1 2 3)) @print{} 123 | |
926 | @end example | |
927 | ||
928 | @c FIXME: What is the @nicode{:} modifier to ~} meant to do? The | |
929 | @c Common Lisp spec says it's a minimum of 1 iteration, but the | |
930 | @c format.scm code seems to merely make it have MAXREPS default to 1. | |
931 | ||
932 | Iterations can be nested, an inner iteration operates in the same way | |
933 | as described, but of course on the arguments the outer iteration | |
934 | provides it. This can be used to work into nested list structures. | |
935 | For example in the following the inner @nicode{~@{~d~@}x} is applied | |
936 | to @code{(1 2)} then @code{(3 4 5)} etc. | |
937 | ||
938 | @example | |
939 | (format #t "~@{~@{~d~@}x~@}" '((1 2) (3 4 5))) @print{} 12x345x | |
940 | @end example | |
941 | ||
80a894c9 KR |
942 | See also @nicode{~^} below for escaping from iteration. |
943 | ||
76d3f3d4 KR |
944 | @item @nicode{~[} @nicode{~;} @nicode{~]} |
945 | Conditional. Parameter: @var{selector}. | |
946 | ||
947 | A conditional block is delimited by @nicode{~[} and @nicode{~]}, and | |
948 | @nicode{~;} separates clauses within the block. @nicode{~[} takes an | |
949 | integer argument and that number clause is used. The first clause is | |
950 | number 0. | |
951 | ||
952 | @example | |
953 | (format #f "~[peach~;banana~;mango~]" 1) @result{} "banana" | |
954 | @end example | |
955 | ||
956 | The @var{selector} parameter can be used for the clause number, | |
957 | instead of taking an argument. | |
958 | ||
959 | @example | |
960 | (format #f "~2[peach~;banana~;mango~]") @result{} "mango" | |
961 | @end example | |
962 | ||
963 | If the clause number is out of range then nothing is output. Or the | |
80a894c9 | 964 | last clause can be @nicode{~:;} to use that for a number out of range. |
76d3f3d4 KR |
965 | |
966 | @example | |
967 | (format #f "~[banana~;mango~]" 99) @result{} "" | |
968 | (format #f "~[banana~;mango~:;fruit~]" 99) @result{} "fruit" | |
969 | @end example | |
970 | ||
80a894c9 KR |
971 | @nicode{~:[} treats the argument as a flag, and expects two clauses. |
972 | The first is used if the argument is @code{#f} or the second | |
973 | otherwise. | |
76d3f3d4 KR |
974 | |
975 | @example | |
976 | (format #f "~:[false~;not false~]" #f) @result{} "false" | |
977 | (format #f "~:[false~;not false~]" 'abc) @result{} "not false" | |
978 | ||
979 | (let ((n 3)) | |
980 | (format #t "~d gnu~:[s are~; is~] here" n (= 1 n))) | |
981 | @print{} 3 gnus are here | |
982 | @end example | |
983 | ||
80a894c9 KR |
984 | @nicode{~@@[} also treats the argument as a flag, and expects one |
985 | clause. If the argument is @code{#f} then no output is produced and | |
986 | the argument is consumed, otherwise the clause is used and the | |
987 | argument is not consumed, it's left for the clause. This can be used | |
988 | for instance to suppress output if @code{#f} means something not | |
989 | available. | |
76d3f3d4 KR |
990 | |
991 | @example | |
992 | (format #f "~@@[temperature=~d~]" 27) @result{} "temperature=27" | |
993 | (format #f "~@@[temperature=~d~]" #f) @result{} "" | |
994 | @end example | |
995 | ||
996 | @item @nicode{~^} | |
997 | Escape. Parameters: @var{val1}, @var{val2}, @var{val3}. | |
998 | ||
999 | Stop formatting if there are no more arguments. This can be used for | |
80a894c9 | 1000 | instance to have a format string adapt to a variable number of |
76d3f3d4 KR |
1001 | arguments. |
1002 | ||
1003 | @example | |
1004 | (format #t "~d~^ ~d" 1) @print{} 1 | |
1005 | (format #t "~d~^ ~d" 1 2) @print{} 1 2 | |
1006 | @end example | |
1007 | ||
1008 | Within a @nicode{~@{} @nicode{~@}} iteration, @nicode{~^} stops the | |
1009 | current iteration step if there are no more arguments to that step, | |
80a894c9 KR |
1010 | but continuing with possible further steps and the rest of the format. |
1011 | This can be used for instance to avoid a separator on the last | |
1012 | iteration, or to adapt to variable length argument lists. | |
76d3f3d4 KR |
1013 | |
1014 | @example | |
1015 | (format #f "~@{~d~^/~@} go" '(1 2 3)) @result{} "1/2/3 go" | |
1016 | (format #f "~:@{ ~d~^~d~@} go" '((1) (2 3))) @result{} " 1 23 go" | |
1017 | @end example | |
1018 | ||
1019 | @c For reference, format.scm doesn't implement that Common Lisp ~:^ | |
1020 | @c modifier which stops the entire iterating of ~:{ or ~@:{. | |
1021 | ||
1022 | @c FIXME: Believe the Common Lisp spec is for ~^ within ~[ ~] | |
1023 | @c conditional to terminate the whole format (or iteration step if in | |
1024 | @c an iteration). But format.scm seems to terminate just the | |
1025 | @c conditional form. | |
1026 | @c | |
1027 | @c (format #f "~[abc~^def~;ghi~] blah" 0) | |
1028 | @c @result{} "abc blah" ;; looks wrong | |
1029 | ||
1030 | @c FIXME: Believe the Common Lisp spec is for ~^ within ~( ~) to end | |
1031 | @c that case conversion and then also terminate the whole format (or | |
1032 | @c iteration step if in an iteration). But format.scm doesn't seem | |
1033 | @c to do that quite right. | |
1034 | @c | |
1035 | @c (format #f "~d ~^ ~d" 1) @result{} "1 " | |
1036 | @c (format #f "~(~d ~^ ~d~)" 1) @result{} ERROR | |
1037 | ||
1038 | Within a @nicode{~?} sub-format, @nicode{~^} operates just on that | |
1039 | sub-format. If it terminates the sub-format then the originating | |
1040 | format will still continue. | |
1041 | ||
1042 | @example | |
1043 | (format #t "~? items" "~d~^ ~d" '(1)) @print{} 1 items | |
1044 | (format #t "~? items" "~d~^ ~d" '(1 2)) @print{} 1 2 items | |
1045 | @end example | |
1046 | ||
1047 | The parameters to @nicode{~^} (which are numbers) change the condition | |
1048 | used to terminate. For a single parameter, termination is when that | |
1049 | value is zero (notice this makes plain @nicode{~^} equivalent to | |
1050 | @nicode{~#^}). For two parameters, termination is when those two are | |
1051 | equal. For three parameters, termination is when @math{@var{val1} | |
1052 | @le{} @var{val2}} and @math{@var{val2} @le{} @var{val3}}. | |
1053 | ||
1054 | @c FIXME: Good examples of these? | |
1055 | ||
1056 | @item @nicode{~q} | |
80a894c9 KR |
1057 | Inquiry message. Insert a copyright message into the output. |
1058 | ||
1059 | @nicode{~:q} inserts the format implementation version. | |
a0e07ba4 NJ |
1060 | @end table |
1061 | ||
76d3f3d4 | 1062 | @sp 1 |
471d2c6d KR |
1063 | It's an error if there are not enough arguments for the escapes in the |
1064 | format string, but any excess arguments are ignored. | |
76d3f3d4 KR |
1065 | |
1066 | Iterations @nicode{~@{} @nicode{~@}} and conditionals @nicode{~[} | |
1067 | @nicode{~;} @nicode{~]} can be nested, but must be properly nested, | |
1068 | meaning the inner form must be entirely within the outer form. So | |
1069 | it's not possible, for instance, to try to conditionalize the endpoint | |
1070 | of an iteration. | |
1071 | ||
1072 | @example | |
1073 | (format #t "~@{ ~[ ... ~] ~@}" ...) ;; good | |
1074 | (format #t "~@{ ~[ ... ~@} ... ~]" ...) ;; bad | |
1075 | @end example | |
1076 | ||
1077 | The same applies to case conversions @nicode{~(} @nicode{~)}, they | |
1078 | must properly nest with respect to iterations and conditionals (though | |
1079 | currently a case conversion cannot nest within another case | |
1080 | conversion). | |
1081 | ||
1082 | When a sub-format (@nicode{~?}) is used, that sub-format string must | |
1083 | be self-contained. It cannot for instance give a @nicode{~@{} to | |
1084 | begin an iteration form and have the @nicode{~@}} up in the | |
1085 | originating format, or similar. | |
a0e07ba4 NJ |
1086 | @end deffn |
1087 | ||
76d3f3d4 KR |
1088 | @sp 1 |
1089 | Guile contains a @code{format} procedure even when the module | |
1090 | @code{(ice-9 format)} is not loaded. The default @code{format} is | |
1091 | @code{simple-format} (@pxref{Writing}), it doesn't support all escape | |
1092 | sequences documented in this section, and will signal an error if you | |
1093 | try to use one of them. The reason for two versions is that the full | |
1094 | @code{format} is fairly large and requires some time to load. | |
1095 | @code{simple-format} is often adequate too. | |
a0e07ba4 NJ |
1096 | |
1097 | ||
6da1534c | 1098 | @node File Tree Walk |
3229f68b | 1099 | @section File Tree Walk |
6da1534c KR |
1100 | @cindex file tree walk |
1101 | ||
1102 | The functions in this section traverse a tree of files and | |
1103 | directories, in a fashion similar to the C @code{ftw} and @code{nftw} | |
1104 | routines (@pxref{Working with Directory Trees,,, libc, GNU C Library | |
1105 | Reference Manual}). | |
1106 | ||
1107 | @example | |
1108 | (use-modules (ice-9 ftw)) | |
1109 | @end example | |
1110 | @sp 1 | |
1111 | ||
1112 | @defun ftw startname proc ['hash-size n] | |
c4e84357 | 1113 | Walk the file system tree descending from @var{startname}, calling |
6da1534c KR |
1114 | @var{proc} for each file and directory. |
1115 | ||
1116 | Hard links and symbolic links are followed. A file or directory is | |
1117 | reported to @var{proc} only once, and skipped if seen again in another | |
1118 | place. One consequence of this is that @code{ftw} is safe against | |
1119 | circularly linked directory structures. | |
1120 | ||
1121 | Each @var{proc} call is @code{(@var{proc} filename statinfo flag)} and | |
1122 | it should return @code{#t} to continue, or any other value to stop. | |
1123 | ||
1124 | @var{filename} is the item visited, being @var{startname} plus a | |
1125 | further path and the name of the item. @var{statinfo} is the return | |
1126 | from @code{stat} (@pxref{File System}) on @var{filename}. @var{flag} | |
1127 | is one of the following symbols, | |
1128 | ||
1129 | @table @code | |
1130 | @item regular | |
1131 | @var{filename} is a file, this includes special files like devices, | |
1132 | named pipes, etc. | |
1133 | ||
1134 | @item directory | |
1135 | @var{filename} is a directory. | |
1136 | ||
1137 | @item invalid-stat | |
1138 | An error occurred when calling @code{stat}, so nothing is known. | |
1139 | @var{statinfo} is @code{#f} in this case. | |
1140 | ||
1141 | @item directory-not-readable | |
1142 | @var{filename} is a directory, but one which cannot be read and hence | |
1143 | won't be recursed into. | |
1144 | ||
1145 | @item symlink | |
1146 | @var{filename} is a dangling symbolic link. Symbolic links are | |
1147 | normally followed and their target reported, the link itself is | |
1148 | reported if the target does not exist. | |
1149 | @end table | |
1150 | ||
1151 | The return value from @code{ftw} is @code{#t} if it ran to completion, | |
1152 | or otherwise the non-@code{#t} value from @var{proc} which caused the | |
1153 | stop. | |
1154 | ||
1155 | Optional argument symbol @code{hash-size} and an integer can be given | |
1156 | to set the size of the hash table used to track items already visited. | |
1157 | (@pxref{Hash Table Reference}) | |
1158 | ||
1159 | @c Actually, it's probably safe to escape from ftw, just need to | |
1160 | @c check it. | |
1161 | @c | |
1162 | In the current implementation, returning non-@code{#t} from @var{proc} | |
1163 | is the only valid way to terminate @code{ftw}. @var{proc} must not | |
1164 | use @code{throw} or similar to escape. | |
1165 | @end defun | |
1166 | ||
1167 | ||
1168 | @defun nftw startname proc ['chdir] ['depth] ['hash-size n] ['mount] ['physical] | |
c4e84357 | 1169 | Walk the file system tree starting at @var{startname}, calling |
6da1534c KR |
1170 | @var{proc} for each file and directory. @code{nftw} has extra |
1171 | features over the basic @code{ftw} described above. | |
1172 | ||
40296bab KR |
1173 | Like @code{ftw}, hard links and symbolic links are followed. A file |
1174 | or directory is reported to @var{proc} only once, and skipped if seen | |
1175 | again in another place. One consequence of this is that @code{nftw} | |
1176 | is safe against circular linked directory structures. | |
6da1534c KR |
1177 | |
1178 | Each @var{proc} call is @code{(@var{proc} filename statinfo flag | |
40296bab | 1179 | base level)} and it should return @code{#t} to continue, or any |
6da1534c KR |
1180 | other value to stop. |
1181 | ||
1182 | @var{filename} is the item visited, being @var{startname} plus a | |
1183 | further path and the name of the item. @var{statinfo} is the return | |
40296bab KR |
1184 | from @code{stat} on @var{filename} (@pxref{File System}). @var{base} |
1185 | is an integer offset into @var{filename} which is where the basename | |
1186 | for this item begins. @var{level} is an integer giving the directory | |
1187 | nesting level, starting from 0 for the contents of @var{startname} (or | |
1188 | that item itself if it's a file). @var{flag} is one of the following | |
1189 | symbols, | |
6da1534c KR |
1190 | |
1191 | @table @code | |
1192 | @item regular | |
40296bab KR |
1193 | @var{filename} is a file, including special files like devices, named |
1194 | pipes, etc. | |
6da1534c KR |
1195 | |
1196 | @item directory | |
1197 | @var{filename} is a directory. | |
1198 | ||
1199 | @item directory-processed | |
1200 | @var{filename} is a directory, and its contents have all been visited. | |
1201 | This flag is given instead of @code{directory} when the @code{depth} | |
1202 | option below is used. | |
1203 | ||
1204 | @item invalid-stat | |
1205 | An error occurred when applying @code{stat} to @var{filename}, so | |
1206 | nothing is known about it. @var{statinfo} is @code{#f} in this case. | |
1207 | ||
1208 | @item directory-not-readable | |
1209 | @var{filename} is a directory, but one which cannot be read and hence | |
1210 | won't be recursed into. | |
1211 | ||
6da1534c | 1212 | @item stale-symlink |
40296bab KR |
1213 | @var{filename} is a dangling symbolic link. Links are normally |
1214 | followed and their target reported, the link itself is reported if its | |
1215 | target does not exist. | |
1216 | ||
1217 | @item symlink | |
1218 | When the @code{physical} option described below is used, this | |
1219 | indicates @var{filename} is a symbolic link whose target exists (and | |
1220 | is not being followed). | |
6da1534c KR |
1221 | @end table |
1222 | ||
1223 | The following optional arguments can be given to modify the way | |
1224 | @code{nftw} works. Each is passed as a symbol (and @code{hash-size} | |
1225 | takes a following integer value). | |
1226 | ||
1227 | @table @asis | |
1228 | @item @code{chdir} | |
1229 | Change to the directory containing the item before calling @var{proc}. | |
1230 | When @code{nftw} returns the original current directory is restored. | |
1231 | ||
40296bab KR |
1232 | Under this option, generally the @var{base} parameter to each |
1233 | @var{proc} call should be used to pick out the base part of the | |
1234 | @var{filename}. The @var{filename} is still a path but with a changed | |
1235 | directory it won't be valid (unless the @var{startname} directory was | |
1236 | absolute). | |
6da1534c KR |
1237 | |
1238 | @item @code{depth} | |
1239 | Visit files ``depth first'', meaning @var{proc} is called for the | |
1240 | contents of each directory before it's called for the directory | |
1241 | itself. Normally a directory is reported first, then its contents. | |
1242 | ||
1243 | Under this option, the @var{flag} to @var{proc} for a directory is | |
1244 | @code{directory-processed} instead of @code{directory}. | |
1245 | ||
1246 | @item @code{hash-size @var{n}} | |
1247 | Set the size of the hash table used to track items already visited. | |
1248 | (@pxref{Hash Table Reference}) | |
1249 | ||
1250 | @item @code{mount} | |
1251 | Don't cross a mount point, meaning only visit items on the same | |
c4e84357 | 1252 | file system as @var{startname} (ie.@: the same @code{stat:dev}). |
6da1534c KR |
1253 | |
1254 | @item @code{physical} | |
1255 | Don't follow symbolic links, instead report them to @var{proc} as | |
40296bab KR |
1256 | @code{symlink}. Dangling links (those whose target doesn't exist) are |
1257 | still reported as @code{stale-symlink}. | |
6da1534c KR |
1258 | @end table |
1259 | ||
1260 | The return value from @code{nftw} is @code{#t} if it ran to | |
1261 | completion, or otherwise the non-@code{#t} value from @var{proc} which | |
1262 | caused the stop. | |
1263 | ||
1264 | @c For reference, one reason not to esacpe is that the current | |
1265 | @c directory is not saved and restored with dynamic-wind. Maybe | |
1266 | @c changing that would be enough to allow escaping. | |
1267 | @c | |
1268 | In the current implementation, returning non-@code{#t} from @var{proc} | |
1269 | is the only valid way to terminate @code{ftw}. @var{proc} must not | |
1270 | use @code{throw} or similar to escape. | |
1271 | @end defun | |
1272 | ||
1273 | ||
2370f809 | 1274 | @node Queues |
3229f68b | 1275 | @section Queues |
d10196fc | 1276 | @cindex queues |
2370f809 KR |
1277 | @tindex Queues |
1278 | ||
1279 | @noindent | |
1280 | The functions in this section are provided by | |
1281 | ||
1282 | @example | |
1283 | (use-modules (ice-9 q)) | |
1284 | @end example | |
1285 | ||
1286 | This module implements queues holding arbitrary scheme objects and | |
1287 | designed for efficient first-in / first-out operations. | |
1288 | ||
1289 | @code{make-q} creates a queue, and objects are entered and removed | |
23f2b9a3 | 1290 | with @code{enq!} and @code{deq!}. @code{q-push!} and @code{q-pop!} |
2370f809 KR |
1291 | can be used too, treating the front of the queue like a stack. |
1292 | ||
1293 | @sp 1 | |
1294 | ||
1295 | @deffn {Scheme Procedure} make-q | |
1296 | Return a new queue. | |
1297 | @end deffn | |
1298 | ||
1299 | @deffn {Scheme Procedure} q? obj | |
1300 | Return @code{#t} if @var{obj} is a queue, or @code{#f} if not. | |
1301 | ||
1302 | Note that queues are not a distinct class of objects but are | |
1303 | implemented with cons cells. For that reason certain list structures | |
1304 | can get @code{#t} from @code{q?}. | |
1305 | @end deffn | |
1306 | ||
1307 | @deffn {Scheme Procedure} enq! q obj | |
1308 | Add @var{obj} to the rear of @var{q}, and return @var{q}. | |
1309 | @end deffn | |
1310 | ||
1311 | @deffn {Scheme Procedure} deq! q | |
1312 | @deffnx {Scheme Procedure} q-pop! q | |
1313 | Remove and return the front element from @var{q}. If @var{q} is | |
1314 | empty, a @code{q-empty} exception is thrown. | |
1315 | ||
1316 | @code{deq!} and @code{q-pop!} are the same operation, the two names | |
1317 | just let an application match @code{enq!} with @code{deq!}, or | |
1318 | @code{q-push!} with @code{q-pop!}. | |
1319 | @end deffn | |
1320 | ||
1321 | @deffn {Scheme Procedure} q-push! q obj | |
1322 | Add @var{obj} to the front of @var{q}, and return @var{q}. | |
1323 | @end deffn | |
1324 | ||
1325 | @deffn {Scheme Procedure} q-length q | |
1326 | Return the number of elements in @var{q}. | |
1327 | @end deffn | |
1328 | ||
1329 | @deffn {Scheme Procedure} q-empty? q | |
1330 | Return true if @var{q} is empty. | |
1331 | @end deffn | |
1332 | ||
1333 | @deffn {Scheme Procedure} q-empty-check q | |
1334 | Throw a @code{q-empty} exception if @var{q} is empty. | |
1335 | @end deffn | |
1336 | ||
1337 | @deffn {Scheme Procedure} q-front q | |
1338 | Return the first element of @var{q} (without removing it). If @var{q} | |
1339 | is empty, a @code{q-empty} exception is thrown. | |
1340 | @end deffn | |
1341 | ||
1342 | @deffn {Scheme Procedure} q-rear q | |
1343 | Return the last element of @var{q} (without removing it). If @var{q} | |
1344 | is empty, a @code{q-empty} exception is thrown. | |
1345 | @end deffn | |
1346 | ||
1347 | @deffn {Scheme Procedure} q-remove! q obj | |
72b3aa56 | 1348 | Remove all occurrences of @var{obj} from @var{q}, and return @var{q}. |
2370f809 KR |
1349 | @var{obj} is compared to queue elements using @code{eq?}. |
1350 | @end deffn | |
1351 | ||
1352 | @sp 1 | |
1353 | @cindex @code{q-empty} | |
1354 | The @code{q-empty} exceptions described above are thrown just as | |
1355 | @code{(throw 'q-empty)}, there's no message etc like an error throw. | |
1356 | ||
1357 | A queue is implemented as a cons cell, the @code{car} containing a | |
1358 | list of queued elements, and the @code{cdr} being the last cell in | |
1359 | that list (for ease of enqueuing). | |
1360 | ||
1361 | @example | |
1362 | (@var{list} . @var{last-cell}) | |
1363 | @end example | |
1364 | ||
1365 | @noindent | |
1366 | If the queue is empty, @var{list} is the empty list and | |
1367 | @var{last-cell} is @code{#f}. | |
1368 | ||
1369 | An application can directly access the queue list if desired, for | |
1370 | instance to search the elements or to insert at a specific point. | |
1371 | ||
1372 | @deffn {Scheme Procedure} sync-q! q | |
1373 | Recompute the @var{last-cell} field in @var{q}. | |
1374 | ||
1375 | All the operations above maintain @var{last-cell} as described, so | |
1376 | normally there's no need for @code{sync-q!}. But if an application | |
1377 | modifies the queue @var{list} then it must either maintain | |
1378 | @var{last-cell} similarly, or call @code{sync-q!} to recompute it. | |
1379 | @end deffn | |
1380 | ||
1381 | ||
458dd501 KR |
1382 | @node Streams |
1383 | @section Streams | |
1384 | @cindex streams | |
1385 | ||
1386 | A stream represents a sequence of values, each of which is calculated | |
1387 | only when required. This allows large or even infinite sequences to | |
1388 | be represented and manipulated with familiar operations like ``car'', | |
1389 | ``cdr'', ``map'' or ``fold''. In such manipulations only as much as | |
1390 | needed is actually held in memory at any one time. The functions in | |
1391 | this section are available from | |
1392 | ||
1393 | @example | |
1394 | (use-modules (ice-9 streams)) | |
1395 | @end example | |
1396 | ||
1397 | Streams are implemented using promises (@pxref{Delayed Evaluation}), | |
1398 | which is how the underlying calculation of values is made only when | |
1399 | needed, and the values then retained so the calculation is not | |
1400 | repeated. | |
1401 | ||
1402 | @noindent | |
1403 | Here is a simple example producing a stream of all odd numbers, | |
1404 | ||
1405 | @example | |
1406 | (define odds (make-stream (lambda (state) | |
1407 | (cons state (+ state 2))) | |
1408 | 1)) | |
1409 | (stream-car odds) @result{} 1 | |
1410 | (stream-car (stream-cdr odds)) @result{} 3 | |
1411 | @end example | |
1412 | ||
1413 | @noindent | |
1414 | @code{stream-map} could be used to derive a stream of odd squares, | |
1415 | ||
1416 | @example | |
1417 | (define (square n) (* n n)) | |
1418 | (define oddsquares (stream-map square odds)) | |
1419 | @end example | |
1420 | ||
1421 | These are infinite sequences, so it's not possible to convert them to | |
1422 | a list, but they could be printed (infinitely) with for example | |
1423 | ||
1424 | @example | |
1425 | (stream-for-each (lambda (n sq) | |
1426 | (format #t "~a squared is ~a\n" n sq)) | |
1427 | odds oddsquares) | |
1428 | @print{} | |
1429 | 1 squared is 1 | |
1430 | 3 squared is 9 | |
1431 | 5 squared is 25 | |
1432 | 7 squared is 49 | |
1433 | @dots{} | |
1434 | @end example | |
1435 | ||
1436 | @sp 1 | |
1437 | @defun make-stream proc initial-state | |
1438 | Return a new stream, formed by calling @var{proc} successively. | |
1439 | ||
1440 | Each call is @code{(@var{proc} @var{state})}, it should return a pair, | |
1441 | the @code{car} being the value for the stream, and the @code{cdr} | |
1442 | being the new @var{state} for the next call. For the first call | |
1443 | @var{state} is the given @var{initial-state}. At the end of the | |
1444 | stream, @var{proc} should return some non-pair object. | |
1445 | @end defun | |
1446 | ||
1447 | @defun stream-car stream | |
1448 | Return the first element from @var{stream}. @var{stream} must not be | |
1449 | empty. | |
1450 | @end defun | |
1451 | ||
1452 | @defun stream-cdr stream | |
1453 | Return a stream which is the second and subsequent elements of | |
1454 | @var{stream}. @var{stream} must not be empty. | |
1455 | @end defun | |
1456 | ||
1457 | @defun stream-null? stream | |
1458 | Return true if @var{stream} is empty. | |
1459 | @end defun | |
1460 | ||
1461 | @defun list->stream list | |
1462 | @defunx vector->stream vector | |
1463 | Return a stream with the contents of @var{list} or @var{vector}. | |
1464 | ||
1465 | @var{list} or @var{vector} should not be modified subsequently, since | |
1466 | it's unspecified whether changes there will be reflected in the stream | |
1467 | returned. | |
1468 | @end defun | |
1469 | ||
1470 | @defun port->stream port readproc | |
1471 | Return a stream which is the values obtained by reading from | |
1472 | @var{port} using @var{readproc}. Each read call is | |
1473 | @code{(@var{readproc} @var{port})}, and it should return an EOF object | |
1474 | (@pxref{Reading}) at the end of input. | |
1475 | ||
1476 | For example a stream of characters from a file, | |
1477 | ||
1478 | @example | |
1479 | (port->stream (open-input-file "/foo/bar.txt") read-char) | |
1480 | @end example | |
1481 | @end defun | |
1482 | ||
1483 | @defun stream->list stream | |
1484 | Return a list which is the entire contents of @var{stream}. | |
1485 | @end defun | |
1486 | ||
1487 | @defun stream->reversed-list stream | |
1488 | Return a list which is the entire contents of @var{stream}, but in | |
1489 | reverse order. | |
1490 | @end defun | |
1491 | ||
1492 | @defun stream->list&length stream | |
5179b0e2 KR |
1493 | Return two values (@pxref{Multiple Values}), being firstly a list |
1494 | which is the entire contents of @var{stream}, and secondly the number | |
1495 | of elements in that list. | |
458dd501 KR |
1496 | @end defun |
1497 | ||
1498 | @defun stream->reversed-list&length stream | |
5179b0e2 KR |
1499 | Return two values (@pxref{Multiple Values}) being firstly a list which |
1500 | is the entire contents of @var{stream}, but in reverse order, and | |
1501 | secondly the number of elements in that list. | |
458dd501 KR |
1502 | @end defun |
1503 | ||
1504 | @defun stream->vector stream | |
1505 | Return a vector which is the entire contents of @var{stream}. | |
1506 | @end defun | |
1507 | ||
1508 | @defun stream-fold proc init stream0 @dots{} streamN | |
1509 | Apply @var{proc} successively over the elements of the given streams, | |
1510 | from first to last until the end of the shortest stream is reached. | |
1511 | Return the result from the last @var{proc} call. | |
1512 | ||
1513 | Each call is @code{(@var{proc} elem0 @dots{} elemN prev)}, where each | |
1514 | @var{elem} is from the corresponding @var{stream}. @var{prev} is the | |
1515 | return from the previous @var{proc} call, or the given @var{init} for | |
1516 | the first call. | |
1517 | @end defun | |
1518 | ||
1519 | @defun stream-for-each proc stream0 @dots{} streamN | |
1520 | Call @var{proc} on the elements from the given @var{stream}s. The | |
1521 | return value is unspecified. | |
1522 | ||
1523 | Each call is @code{(@var{proc} elem0 @dots{} elemN)}, where each | |
1524 | @var{elem} is from the corresponding @var{stream}. | |
1525 | @code{stream-for-each} stops when it reaches the end of the shortest | |
1526 | @var{stream}. | |
1527 | @end defun | |
1528 | ||
1529 | @defun stream-map proc stream0 @dots{} streamN | |
1530 | Return a new stream which is the results of applying @var{proc} to the | |
1531 | elements of the given @var{stream}s. | |
1532 | ||
1533 | Each call is @code{(@var{proc} elem0 @dots{} elemN)}, where each | |
1534 | @var{elem} is from the corresponding @var{stream}. The new stream | |
5179b0e2 | 1535 | ends when the end of the shortest given @var{stream} is reached. |
458dd501 KR |
1536 | @end defun |
1537 | ||
1538 | ||
40296bab KR |
1539 | @node Buffered Input |
1540 | @section Buffered Input | |
1541 | @cindex Buffered input | |
1542 | @cindex Line continuation | |
1543 | ||
1544 | The following functions are provided by | |
1545 | ||
1546 | @example | |
1547 | (use-modules (ice-9 buffered-input)) | |
1548 | @end example | |
1549 | ||
1550 | A buffered input port allows a reader function to return chunks of | |
1551 | characters which are to be handed out on reading the port. A notion | |
1552 | of further input for an application level logical expression is | |
1553 | maintained too, and passed through to the reader. | |
1554 | ||
1555 | @defun make-buffered-input-port reader | |
1556 | Create an input port which returns characters obtained from the given | |
1557 | @var{reader} function. @var{reader} is called (@var{reader} cont), | |
1558 | and should return a string or an EOF object. | |
1559 | ||
1560 | The new port gives precisely the characters returned by @var{reader}, | |
1561 | nothing is added, so if any newline characters or other separators are | |
1562 | desired they must come from the reader function. | |
1563 | ||
1564 | The @var{cont} parameter to @var{reader} is @code{#f} for initial | |
1565 | input, or @code{#t} when continuing an expression. This is an | |
1566 | application level notion, set with | |
1567 | @code{set-buffered-input-continuation?!} below. If the user has | |
1568 | entered a partial expression then it allows @var{reader} for instance | |
1569 | to give a different prompt to show more is required. | |
1570 | @end defun | |
1571 | ||
1572 | @defun make-line-buffered-input-port reader | |
1573 | @cindex Line buffered input | |
1574 | Create an input port which returns characters obtained from the | |
1575 | specified @var{reader} function, similar to | |
1576 | @code{make-buffered-input-port} above, but where @var{reader} is | |
1577 | expected to be a line-oriented. | |
1578 | ||
1579 | @var{reader} is called (@var{reader} cont), and should return a string | |
1580 | or an EOF object as above. Each string is a line of input without a | |
1581 | newline character, the port code inserts a newline after each string. | |
1582 | @end defun | |
1583 | ||
1584 | @defun set-buffered-input-continuation?! port cont | |
1585 | Set the input continuation flag for a given buffered input | |
1586 | @var{port}. | |
1587 | ||
1588 | An application uses this by calling with a @var{cont} flag of | |
1589 | @code{#f} when beginning to read a new logical expression. For | |
1590 | example with the Scheme @code{read} function (@pxref{Scheme Read}), | |
1591 | ||
1592 | @example | |
1593 | (define my-port (make-buffered-input-port my-reader)) | |
1594 | ||
1595 | (set-buffered-input-continuation?! my-port #f) | |
1596 | (let ((obj (read my-port))) | |
1597 | ... | |
1598 | @end example | |
1599 | @end defun | |
1600 | ||
1601 | ||
a0e07ba4 NJ |
1602 | @c Local Variables: |
1603 | @c TeX-master: "guile.texi" | |
1604 | @c End: |