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@page
@node Data Types
@chapter Data Types for Generic Use

This chapter describes all the data types that Guile provides for
``generic use''.

One of the great strengths of Scheme is that there is no straightforward
distinction between ``data'' and ``functionality''.  For example,
Guile's support for dynamic linking could be described

@itemize
@item
either in a ``data-centric'' way, as the behaviour and properties of the
``dynamically linked object'' data type, and the operations that may be
applied to instances of this type

@item
or in a ``functionality-centric'' way, as the set of procedures that
constitute Guile's support for dynamic linking, in the context of the
module system.
@end itemize

The contents of this chapter are, therefore, a matter of judgement.  By
``generic use'', we mean to select those data types whose typical use as
@emph{data} in a wide variety of programming contexts is more important
than their use in the implementation of a particular piece of
@emph{functionality}.

@ifinfo
The following menu
@end ifinfo
@iftex
The table of contents for this chapter
@end iftex
@ifhtml
The following table of contents
@end ifhtml
shows the data types that are documented in this chapter.  The final
section of this chapter lists all the core Guile data types that are not
documented here, and provides links to the ``functionality-centric''
sections of this manual that cover them.

@menu
* Booleans::                    True/false values.
* Numbers::                     Numerical data types.
* Characters::                  New character names.
* Strings::                     Special things about strings.
* Regular Expressions::         Pattern matching and substitution.
* Symbols and Variables::       Manipulating the Scheme symbol table.
* Keywords::                    Self-quoting, customizable display keywords.
* Pairs::                       Scheme's basic building block.
* Lists::                       Special list functions supported by Guile.
* Records::
* Structures::
* Arrays::
* Association Lists and Hash Tables::
* Vectors::
* Hooks::                       User-customizable event lists.
* Other Data Types::            Data types that are documented elsewhere.
@end menu


@node Booleans
@section Booleans

The two boolean values are @code{#t} for true and @code{#f} for false.

Boolean values are returned by predicate procedures, such as the general
equality predicates @code{eq?}, @code{eqv?} and @code{equal?}
(@pxref{Equality}) and numerical and string comparison operators like
@code{string=?} (REFFIXME) and @code{<=} (REFFIXME).

@lisp
(<= 3 8)
@result{}
#t

(<= 3 -3)
@result{}
#f

(equal? "house" "houses")
@result{}
#f

(eq? #f #f)
@result{}
#t
@end lisp

In test condition contexts like @code{if} (REFFIXME) and @code{cond}
(REFFIXME), where a group of subexpressions will be evaluated only if a
@var{condition} expression evaluates to ``true'', ``true'' means any
value at all except @code{#f}.

@lisp
(if #t "yes" "no")
@result{}
"yes"

(if 0 "yes" "no")
@result{}
"yes"

(if #f "yes" "no")
@result{}
"no"
@end lisp

A result of this asymmetry is that typical Scheme source code more often
uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
represent an @code{if} or @code{cond} false value, whereas @code{#t} is
not necessary to represent an @code{if} or @code{cond} true value.

It is important to note that @code{#f} is @strong{not} equivalent to any
other Scheme value.  In particular, @code{#f} is not the same as the
number 0 (like in C and C++), and not the same as the ``empty list''
(like in some Lisp dialects).

The @code{not} procedure returns the boolean inverse of its argument:

@c docstring begin (texi-doc-string "guile" "not")
@deffn primitive not x
Return @code{#t} iff @var{x} is @code{#f}, else return @code{#f}.
@end deffn

The @code{boolean?} procedure is a predicate that returns @code{#t} if
its argument is one of the boolean values, otherwise @code{#f}.

@c docstring begin (texi-doc-string "guile" "boolean?")
@deffn primitive boolean? obj
Return @code{#t} iff @var{obj} is either @code{#t} or @code{#f}.
@end deffn


@node Numbers
@section Numerical data types

Guile supports a rich ``tower'' of numerical types --- integer,
rational, real and complex --- and provides an extensive set of
mathematical and scientific functions for operating on numerical
data.  This section of the manual documents those types and functions.

You may also find it illuminating to read R5RS's presentation of numbers
in Scheme, which is particularly clear and accessible: see
@xref{Numbers,,,r5rs}.

@menu
* Numerical Tower::             Scheme's numerical "tower".
* Integers::                    Whole numbers.
* Reals and Rationals::         Real and rational numbers.
* Complex Numbers::             Complex numbers.
* Exactness::                   Exactness and inexactness.
* Number Syntax::		Read syntax for numerical data.
* Integer Operations::          Operations on integer values.
* Comparison::                  Comparison predicates.
* Conversion::                  Converting numbers to and from strings.
* Complex::                     Complex number operations.
* Arithmetic::                  Arithmetic functions.
* Scientific::                  Scientific functions.
* Primitive Numerics::          Primitive numeric functions.
* Bitwise Operations::          Logical AND, OR, NOT, and so on.
* Random::                      Random number generation.
@end menu


@node Numerical Tower
@subsection Scheme's Numerical ``Tower''

Scheme's numerical ``tower'' consists of the following categories of
numbers:

@itemize
@item
integers (whole numbers)

@item
rationals (the set of numbers that can be expressed as P/Q where P and Q
are integers)

@item
real numbers (the set of numbers that describes all possible positions
along a one dimensional line)

@item
complex numbers (the set of numbers that describes all possible
positions in a two dimensional space)
@end itemize

It is called a tower because each category ``sits on'' the one that
follows it, in the sense that every integer is also a rational, every
rational is also real, and every real number is also a complex number
(but with zero imaginary part).

Of these, Guile implements integers, reals and complex numbers as
distinct types.  Rationals are implemented as regards the read syntax
for rational numbers that is specified by R5RS, but are immediately
converted by Guile to the corresponding real number.

The @code{number?} predicate may be applied to any Scheme value to
discover whether the value is any of the supported numerical types.

@c docstring begin (texi-doc-string "guile" "number?")
@deffn primitive number? obj
Return @code{#t} if @var{obj} is any kind of number, @code{#f} else.
@end deffn

For example:

@lisp
(number? 3)
@result{}
#t

(number? "hello there!")
@result{}
#f

(define pi 3.141592654)
(number? pi)
@result{}
#t
@end lisp

The next few subsections document each of Guile's numerical data types
in detail.


@node Integers
@subsection Integers

Integers are whole numbers, that is numbers with no fractional part,
such as 2, 83 and -3789.

Integers in Guile can be arbitrarily big, as shown by the following
example.

@lisp
(define (factorial n)
  (let loop ((n n) (product 1))
    (if (= n 0)
        product
        (loop (- n 1) (* product n)))))

(factorial 3)
@result{}
6

(factorial 20)
@result{}
2432902008176640000

(- (factorial 45))
@result{}
-119622220865480194561963161495657715064383733760000000000
@end lisp

Readers whose background is in programming languages where integers are
limited by the need to fit into just 4 or 8 bytes of memory may find
this surprising, or suspect that Guile's representation of integers is
inefficient.  In fact, Guile achieves a near optimal balance of
convenience and efficiency by using the host computer's native
representation of integers where possible, and a more general
representation where the required number does not fit in the native
form.  Conversion between these two representations is automatic and
completely invisible to the Scheme level programmer.

@c REFFIXME Maybe point here to discussion of handling immediates/bignums
@c on the C level, where the conversion is not so automatic - NJ

@c docstring begin (texi-doc-string "guile" "integer?")
@deffn primitive integer? obj
Return @code{#t} if @var{obj} is an integer number, @code{#f} else.

@lisp
(integer? 487)
@result{}
#t

(integer? -3.4)
@result{}
#f
@end lisp
@end deffn


@node Reals and Rationals
@subsection Real and Rational Numbers

Mathematically, the real numbers are the set of numbers that describe
all possible points along a continuous, infinite, one-dimensional line.
The rational numbers are the set of all numbers that can be written as
fractions P/Q, where P and Q are integers.  All rational numbers are
also real, but there are real numbers that are not rational, for example
the square root of 2, and pi.

Guile represents both real and rational numbers approximately using a
floating point encoding with limited precision.  Even though the actual
encoding is in binary, it may be helpful to think of it as a decimal
number with a limited number of significant figures and a decimal point
somewhere, since this corresponds to the standard notation for non-whole
numbers.  For example:

@lisp
0.34
-0.00000142857931198
-5648394822220000000000.0
4.0
@end lisp

The limited precision of Guile's encoding means that any ``real'' number
in Guile can be written in a rational form, by multiplying and then dividing
by sufficient powers of 10 (or in fact, 2).  For example,
@code{-0.00000142857931198} is the same as @code{142857931198} divided by
@code{100000000000000000}.  In Guile's current incarnation, therefore,
the @code{rational?} and @code{real?} predicates are equivalent.

Another aspect of this equivalence is that Guile currently does not
preserve the exactness that is possible with rational arithmetic.
If such exactness is needed, it is of course possible to implement
exact rational arithmetic at the Scheme level using Guile's arbitrary
size integers.

A planned future revision of Guile's numerical tower will make it
possible to implement exact representations and arithmetic for both
rational numbers and real irrational numbers such as square roots,
and in such a way that the new kinds of number integrate seamlessly
with those that are already implemented.

@c docstring begin (texi-doc-string "guile" "real?")
@deffn primitive real? obj
Return @code{#t} if @var{obj} is a real number, @code{#f} else.
Note that the sets of integer and rational values form subsets
of the set of real numbers, so the predicate will also be fulfilled
if @var{obj} is an integer number or a rational number.
@end deffn

@c docstring begin (texi-doc-string "guile" "rational?")
@deffn primitive rational? obj
Return @code{#t} if @var{obj} is a rational number, @code{#f} else.
Note that the set of integer values forms a subset of the set of
rational numbers, so the predicate will also be fulfilled if @var{obj}
is an integer number.
@end deffn


@node Complex Numbers
@subsection Complex Numbers

Complex numbers are the set of numbers that describe all possible points
in a two-dimensional space.  The two coordinates of a particular point
in this space are known as the @dfn{real} and @dfn{imaginary} parts of
the complex number that describes that point.

In Guile, complex numbers are written in rectangular form as the sum of
their real and imaginary parts, using the symbol @code{i} to indicate
the imaginary part.

@lisp
3+4i
@result{}
3.0+4.0i

(* 3-8i 2.3+0.3i)
@result{}
9.3-17.5i
@end lisp

Guile represents a complex number as a pair of numbers both of which are
real, so the real and imaginary parts of a complex number have the same
properties of inexactness and limited precision as single real numbers.

@c docstring begin (texi-doc-string "guile" "complex?")
@deffn primitive complex? obj
Return @code{#t} if @var{obj} is a complex number, @code{#f} else.
Note that the sets of real, rational and integer values form subsets of
the set of complex numbers, so the predicate will also be fulfilled if
@var{obj} is a real, rational or integer number.
@end deffn


@node Exactness
@subsection Exact and Inexact Numbers

R5RS requires that a calculation involving inexact numbers always
produces an inexact result.  To meet this requirement, Guile
distinguishes between an exact integer value such as @code{5} and the
corresponding inexact real value which, to the limited precision
available, has no fractional part, and is printed as @code{5.0}.  Guile
will only convert the latter value to the former when forced to do so by
an invocation of the @code{inexact->exact} procedure.

@c docstring begin (texi-doc-string "guile" "exact?")
@deffn primitive exact? x
Return #t if X is an exact number, #f otherwise.
@end deffn

@c docstring begin (texi-doc-string "guile" "inexact?")
@deffn primitive inexact? x
Return #t if X is an inexact number, #f else.
@end deffn

@c docstring begin (texi-doc-string "guile" "inexact->exact")
@deffn primitive inexact->exact z
Returns an exact number that is numerically closest to Z.
@end deffn

@c begin (texi-doc-string "guile" "exact->inexact")
@deffn primitive exact->inexact
@end deffn


@node Number Syntax
@subsection Read Syntax for Numerical Data

The read syntax for integers is a string of digits, optionally
preceded by a minus or plus character, a code indicating the
base in which the integer is encoded, and a code indicating whether
the number is exact or inexact.  The supported base codes are:

@itemize @bullet
@item
@code{#b}, @code{#B} --- the integer is written in binary (base 2)

@item
@code{#o}, @code{#O} --- the integer is written in octal (base 8)

@item
@code{#d}, @code{#D} --- the integer is written in decimal (base 10)

@item
@code{#x}, @code{#X} --- the integer is written in hexadecimal (base 16).
@end itemize

If the base code is omitted, the integer is assumed to be decimal.  The
following examples show how these base codes are used.

@lisp
-13
@result{}
-13

#d-13
@result{}
-13

#x-13
@result{}
-19

#b+1101
@result{}
13

#o377
@result{}
255
@end lisp

The codes for indicating exactness (which can, incidentally, be applied
to all numerical values) are:

@itemize @bullet
@item
@code{#e}, @code{#E} --- the number is exact

@item
@code{#i}, @code{#I} --- the number is inexact.
@end itemize

If the exactness indicator is omitted, the integer is assumed to be exact,
since Guile's internal representation for integers is always exact.
Real numbers have limited precision similar to the precision of the
@code{double} type in C.  A consequence of the limited precision is that
all real numbers in Guile are also rational, since any number R with a
limited number of decimal places, say N, can be made into an integer by
multiplying by 10^N.


@node Integer Operations
@subsection Operations on Integer Values

@c docstring begin (texi-doc-string "guile" "odd?")
@deffn primitive odd? n
Return #t if N is an odd number, #f otherwise.
@end deffn

@c docstring begin (texi-doc-string "guile" "even?")
@deffn primitive even? n
Return #t if N is an even number, #f otherwise.
@end deffn

@c begin (texi-doc-string "guile" "quotient")
@deffn primitive quotient
@end deffn

@c begin (texi-doc-string "guile" "remainder")
@deffn primitive remainder
@end deffn

@c begin (texi-doc-string "guile" "modulo")
@deffn primitive modulo
@end deffn

@c begin (texi-doc-string "guile" "gcd")
@deffn primitive gcd
@end deffn

@c begin (texi-doc-string "guile" "lcm")
@deffn primitive lcm
@end deffn


@node Comparison
@subsection Comparison Predicates

@c begin (texi-doc-string "guile" "=")
@deffn primitive =
@end deffn

@c begin (texi-doc-string "guile" "<")
@deffn primitive <
@end deffn

@c begin (texi-doc-string "guile" ">")
@deffn primitive >
@end deffn

@c begin (texi-doc-string "guile" "<=")
@deffn primitive <=
@end deffn

@c begin (texi-doc-string "guile" ">=")
@deffn primitive >=
@end deffn

@c begin (texi-doc-string "guile" "zero?")
@deffn primitive zero?
@end deffn

@c begin (texi-doc-string "guile" "positive?")
@deffn primitive positive?
@end deffn

@c begin (texi-doc-string "guile" "negative?")
@deffn primitive negative?
@end deffn


@node Conversion
@subsection Converting Numbers To and From Strings

@c docstring begin (texi-doc-string "guile" "number->string")
@deffn primitive number->string n [radix]
Return a string holding the external representation of the
number N in the given RADIX.  If N is inexact, a radix of 10
will be used.
@end deffn

@c docstring begin (texi-doc-string "guile" "string->number")
@deffn primitive string->number string [radix]
Returns a number of the maximally precise representation
expressed by the given STRING. RADIX must be an exact integer,
either 2, 8, 10, or 16. If supplied, RADIX is a default radix
that may be overridden by an explicit radix prefix in STRING
(e.g. "#o177"). If RADIX is not supplied, then the default
radix is 10. If string is not a syntactically valid notation
for a number, then `string->number' returns #f.  (r5rs)
@end deffn


@node Complex
@subsection Complex Number Operations

@c docstring begin (texi-doc-string "guile" "make-rectangular")
@deffn primitive make-rectangular real imaginary
Return a complex number constructed of the given REAL and
IMAGINARY parts.
@end deffn

@c docstring begin (texi-doc-string "guile" "make-polar")
@deffn primitive make-polar x y
Return the complex number X * e^(i * Y).
@end deffn

@c begin (texi-doc-string "guile" "real-part")
@deffn primitive real-part
@end deffn

@c begin (texi-doc-string "guile" "imag-part")
@deffn primitive imag-part
@end deffn

@c begin (texi-doc-string "guile" "magnitude")
@deffn primitive magnitude
@end deffn

@c begin (texi-doc-string "guile" "angle")
@deffn primitive angle
@end deffn


@node Arithmetic
@subsection Arithmetic Functions

@c begin (texi-doc-string "guile" "+")
@deffn primitive +
@end deffn

@c begin (texi-doc-string "guile" "-")
@deffn primitive -
@end deffn

@c begin (texi-doc-string "guile" "*")
@deffn primitive *
@end deffn

@c begin (texi-doc-string "guile" "/")
@deffn primitive /
@end deffn

@c begin (texi-doc-string "guile" "abs")
@deffn primitive abs
@end deffn

@c begin (texi-doc-string "guile" "max")
@deffn primitive max
@end deffn

@c begin (texi-doc-string "guile" "min")
@deffn primitive min
@end deffn

@c begin (texi-doc-string "guile" "truncate")
@deffn primitive truncate
@end deffn

@c begin (texi-doc-string "guile" "round")
@deffn primitive round
@end deffn

@c begin (texi-doc-string "guile" "floor")
@deffn primitive floor
@end deffn

@c begin (texi-doc-string "guile" "ceiling")
@deffn primitive ceiling
@end deffn


@node Scientific
@subsection Scientific Functions

The following procedures accept any kind of number as arguments,
including complex numbers.

@c begin (texi-doc-string "guile" "sqrt")
@deffn procedure sqrt z
Return the square root of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "expt")
@deffn procedure expt z1 z2
Return @var{z1} raised to the power of @var{z2}.
@end deffn

@c begin (texi-doc-string "guile" "sin")
@deffn procedure sin z
Return the sine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "cos")
@deffn procedure cos z
Return the cosine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "tan")
@deffn procedure tan z
Return the tangent of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "asin")
@deffn procedure asin z
Return the arcsine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "acos")
@deffn procedure acos z
Return the arccosine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "atan")
@deffn procedure atan z
Return the arctangent of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "exp")
@deffn procedure exp z
Return e to the power of @var{z}, where e is the base of natural
logarithms (2.71828@dots{}).
@end deffn

@c begin (texi-doc-string "guile" "log")
@deffn procedure log z
Return the natural logarithm of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "log10")
@deffn procedure log10 z
Return the base 10 logarithm of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "sinh")
@deffn procedure sinh z
Return the hyperbolic sine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "cosh")
@deffn procedure cosh z
Return the hyperbolic cosine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "tanh")
@deffn procedure tanh z
Return the hyperbolic tangent of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "asinh")
@deffn procedure asinh z
Return the hyperbolic arcsine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "acosh")
@deffn procedure acosh z
Return the hyperbolic arccosine of @var{z}.
@end deffn

@c begin (texi-doc-string "guile" "atanh")
@deffn procedure atanh z
Return the hyperbolic arctangent of @var{z}.
@end deffn


@node Primitive Numerics
@subsection Primitive Numeric Functions

Many of Guile's numeric procedures which accept any kind of numbers as
arguments, including complex numbers, are implemented as Scheme
procedures that use the following real number-based primitives.  These
primitives signal an error if they are called with complex arguments.

@c begin (texi-doc-string "guile" "$abs")
@deffn primitive $abs x
Return the absolute value of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$sqrt")
@deffn primitive $sqrt x
Return the square root of @var{x}.
@end deffn

@c docstring begin (texi-doc-string "guile" "$expt")
@deffn primitive $expt x y
Return @var{x} raised to the power of @var{y}. This
procedure does not accept complex arguments.
@end deffn

@c begin (texi-doc-string "guile" "$sin")
@deffn primitive $sin x
Return the sine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$cos")
@deffn primitive $cos x
Return the cosine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$tan")
@deffn primitive $tan x
Return the tangent of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$asin")
@deffn primitive $asin x
Return the arcsine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$acos")
@deffn primitive $acos x
Return the arccosine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$atan")
@deffn primitive $atan x
Return the arctangent of @var{x} in the range -PI/2 to PI/2.
@end deffn

@c docstring begin (texi-doc-string "guile" "$atan2")
@deffn primitive $atan2 x y
Return the arc tangent of the two arguments @var{x} and
@var{y}. This is similar to calculating the arc tangent of
@var{x} / @var{y}, except that the signs of both arguments
are used to determine the quadrant of the result. This
procedure does not accept complex arguments.
@end deffn

@c begin (texi-doc-string "guile" "$exp")
@deffn primitive $exp x
Return e to the power of @var{x}, where e is the base of natural
logarithms (2.71828@dots{}).
@end deffn

@c begin (texi-doc-string "guile" "$log")
@deffn primitive $log x
Return the natural logarithm of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$sinh")
@deffn primitive $sinh x
Return the hyperbolic sine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$cosh")
@deffn primitive $cosh x
Return the hyperbolic cosine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$tanh")
@deffn primitive $tanh x
Return the hyperbolic tangent of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$asinh")
@deffn primitive $asinh x
Return the hyperbolic arcsine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$acosh")
@deffn primitive $acosh x
Return the hyperbolic arccosine of @var{x}.
@end deffn

@c begin (texi-doc-string "guile" "$atanh")
@deffn primitive $atanh x
Return the hyperbolic arctangent of @var{x}.
@end deffn


@node Bitwise Operations
@subsection Bitwise Operations

@c docstring begin (texi-doc-string "guile" "logand")
@deffn primitive logand n1 n2
Returns the integer which is the bit-wise AND of the two integer
arguments.

Example:
@lisp
(number->string (logand #b1100 #b1010) 2)
   @result{} "1000"
@end lisp
@end deffn

@c docstring begin (texi-doc-string "guile" "logior")
@deffn primitive logior n1 n2
Returns the integer which is the bit-wise OR of the two integer
arguments.

Example:
@lisp
(number->string (logior #b1100 #b1010) 2)
   @result{} "1110"
@end lisp
@end deffn

@c docstring begin (texi-doc-string "guile" "logxor")
@deffn primitive logxor n1 n2
Returns the integer which is the bit-wise XOR of the two integer
arguments.

Example:
@lisp
(number->string (logxor #b1100 #b1010) 2)
   @result{} "110"
@end lisp
@end deffn

@c docstring begin (texi-doc-string "guile" "lognot")
@deffn primitive lognot n
Returns the integer which is the 2s-complement of the integer argument.

Example:
@lisp
(number->string (lognot #b10000000) 2)
   @result{} "-10000001"
(number->string (lognot #b0) 2)
   @result{} "-1"
@end lisp
@end deffn

@c ARGFIXME j/n1 k/n2
@c docstring begin (texi-doc-string "guile" "logtest")
@deffn primitive logtest n1 n2
@example
(logtest j k) @equiv{} (not (zero? (logand j k)))

(logtest #b0100 #b1011) @result{} #f
(logtest #b0100 #b0111) @result{} #t
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "logbit?")
@deffn primitive logbit? index j
@example
(logbit? index j) @equiv{} (logtest (integer-expt 2 index) j)

(logbit? 0 #b1101) @result{} #t
(logbit? 1 #b1101) @result{} #f
(logbit? 2 #b1101) @result{} #t
(logbit? 3 #b1101) @result{} #t
(logbit? 4 #b1101) @result{} #f
@end example
@end deffn

@c ARGFIXME n/int cnt/count
@c docstring begin (texi-doc-string "guile" "ash")
@deffn primitive ash n cnt
The function ash performs an arithmetic shift left by CNT bits
(or shift right, if CNT is negative).  'Arithmetic' means, that
the function does not guarantee to keep the bit structure of N,
but rather guarantees that the result will always be rounded
towards minus infinity.  Therefore, the results of ash and a
corresponding bitwise shift will differ if N is negative.

Formally, the function returns an integer equivalent to
@code{(inexact->exact (floor (* N (expt 2 CNT))))}.@refill

Example:
@lisp
(number->string (ash #b1 3) 2)
   @result{} "1000"
(number->string (ash #b1010 -1) 2)
   @result{} "101"
@end lisp
@end deffn

@c docstring begin (texi-doc-string "guile" "logcount")
@deffn primitive logcount n
Returns the number of bits in integer @var{n}.  If integer is positive,
the 1-bits in its binary representation are counted.  If negative, the
0-bits in its two's-complement binary representation are counted.  If 0,
0 is returned.

Example:
@lisp
(logcount #b10101010)
   @result{} 4
(logcount 0)
   @result{} 0
(logcount -2)
   @result{} 1
@end lisp
@end deffn

@c docstring begin (texi-doc-string "guile" "integer-length")
@deffn primitive integer-length n
Returns the number of bits neccessary to represent @var{n}.

Example:
@lisp
(integer-length #b10101010)
   @result{} 8
(integer-length 0)
   @result{} 0
(integer-length #b1111)
   @result{} 4
@end lisp
@end deffn

@c docstring begin (texi-doc-string "guile" "integer-expt")
@deffn primitive integer-expt n k
Returns @var{n} raised to the non-negative integer exponent @var{k}.

Example:
@lisp
(integer-expt 2 5)
   @result{} 32
(integer-expt -3 3)
   @result{} -27
@end lisp
@end deffn

@c docstring begin (texi-doc-string "guile" "bit-extract")
@deffn primitive bit-extract n start end
Returns the integer composed of the @var{start} (inclusive) through
@var{end} (exclusive) bits of @var{n}.  The @var{start}th bit becomes
the 0-th bit in the result.@refill

Example:
@lisp
(number->string (bit-extract #b1101101010 0 4) 2)
   @result{} "1010"
(number->string (bit-extract #b1101101010 4 9) 2)
   @result{} "10110"
@end lisp
@end deffn


@node Random
@subsection Random Number Generation

@c docstring begin (texi-doc-string "guile" "copy-random-state")
@deffn primitive copy-random-state [state]
Return a copy of the random state @var{state}.
@end deffn

@c docstring begin (texi-doc-string "guile" "random")
@deffn primitive random n [state]
Return a number in [0,N).
Accepts a positive integer or real n and returns a
number of the same type between zero (inclusive) and
N (exclusive). The values returned have a uniform
distribution.
The optional argument @var{state} must be of the type produced
by @code{seed->random-state}. It defaults to the value of the
variable @var{*random-state*}. This object is used to maintain
the state of the pseudo-random-number generator and is altered
as a side effect of the random operation.
@end deffn

@c docstring begin (texi-doc-string "guile" "random:exp")
@deffn primitive random:exp [state]
Returns an inexact real in an exponential distribution with mean 1.
For an exponential distribution with mean u use (* u (random:exp)).
@end deffn

@c docstring begin (texi-doc-string "guile" "random:hollow-sphere!")
@deffn primitive random:hollow-sphere! v [state]
Fills vect with inexact real random numbers
the sum of whose squares is equal to 1.0.
Thinking of vect as coordinates in space of
dimension n = (vector-length vect), the coordinates
are uniformly distributed over the surface of the
unit n-shere.
@end deffn

@c docstring begin (texi-doc-string "guile" "random:normal")
@deffn primitive random:normal [state]
Returns an inexact real in a normal distribution.
The distribution used has mean 0 and standard deviation 1.
For a normal distribution with mean m and standard deviation
d use @code{(+ m (* d (random:normal)))}.
@end deffn

@c docstring begin (texi-doc-string "guile" "random:normal-vector!")
@deffn primitive random:normal-vector! v [state]
Fills vect with inexact real random numbers that are
independent and standard normally distributed
(i.e., with mean 0 and variance 1).
@end deffn

@c docstring begin (texi-doc-string "guile" "random:solid-sphere!")
@deffn primitive random:solid-sphere! v [state]
Fills vect with inexact real random numbers
the sum of whose squares is less than 1.0.
Thinking of vect as coordinates in space of
dimension n = (vector-length vect), the coordinates
are uniformly distributed within the unit n-shere.
The sum of the squares of the numbers is returned.
@end deffn

@c docstring begin (texi-doc-string "guile" "random:uniform")
@deffn primitive random:uniform [state]
Returns a uniformly distributed inexact real random number in [0,1).
@end deffn

@c docstring begin (texi-doc-string "guile" "seed->random-state")
@deffn primitive seed->random-state seed
Return a new random state using @var{seed}.
@end deffn


@node Characters
@section Characters

Most of the characters in the ASCII character set may be referred to by
name: for example, @code{#\tab}, @code{#\esc}, @code{#\stx}, and so on.
The following table describes the ASCII names for each character.

@multitable @columnfractions .25 .25 .25 .25
@item 0 = @code{#\nul}
 @tab 1 = @code{#\soh}
 @tab 2 = @code{#\stx}
 @tab 3 = @code{#\etx}
@item 4 = @code{#\eot}
 @tab 5 = @code{#\enq}
 @tab 6 = @code{#\ack}
 @tab 7 = @code{#\bel}
@item 8 = @code{#\bs}
 @tab 9 = @code{#\ht}
 @tab 10 = @code{#\nl}
 @tab 11 = @code{#\vt}
@item 12 = @code{#\np}
 @tab 13 = @code{#\cr}
 @tab 14 = @code{#\so}
 @tab 15 = @code{#\si}
@item 16 = @code{#\dle}
 @tab 17 = @code{#\dc1}
 @tab 18 = @code{#\dc2}
 @tab 19 = @code{#\dc3}
@item 20 = @code{#\dc4}
 @tab 21 = @code{#\nak}
 @tab 22 = @code{#\syn}
 @tab 23 = @code{#\etb}
@item 24 = @code{#\can}
 @tab 25 = @code{#\em}
 @tab 26 = @code{#\sub}
 @tab 27 = @code{#\esc}
@item 28 = @code{#\fs}
 @tab 29 = @code{#\gs}
 @tab 30 = @code{#\rs}
 @tab 31 = @code{#\us}
@item 32 = @code{#\sp}
@end multitable

The @code{delete} character (octal 177) may be referred to with the name
@code{#\del}.

Several characters have more than one name:

@itemize @bullet
@item
#\space, #\sp
@item
#\newline, #\nl
@item
#\tab, #\ht
@item
#\backspace, #\bs
@item
#\return, #\cr
@item
#\page, #\np
@item
#\null, #\nul
@end itemize

@c docstring begin (texi-doc-string "guile" "char?")
@deffn primitive char? x
Return @code{#t} iff @var{x} is a character, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char=?")
@deffn primitive char=? x y
Return @code{#t} iff @var{x} is the same character as @var{y}, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char<?")
@deffn primitive char<? x y
Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence,
else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char<=?")
@deffn primitive char<=? x y
Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
ASCII sequence, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char>?")
@deffn primitive char>? x y
Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII
sequence, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char>=?")
@deffn primitive char>=? x y
Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
ASCII sequence, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-ci=?")
@deffn primitive char-ci=? x y
Return @code{#t} iff @var{x} is the same character as @var{y} ignoring
case, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-ci<?")
@deffn primitive char-ci<? x y
Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence
ignoring case, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-ci<=?")
@deffn primitive char-ci<=? x y
Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
ASCII sequence ignoring case, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-ci>?")
@deffn primitive char-ci>? x y
Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII
sequence ignoring case, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-ci>=?")
@deffn primitive char-ci>=? x y
Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
ASCII sequence ignoring case, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-alphabetic?")
@deffn primitive char-alphabetic? chr
Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
Alphabetic means the same thing as the isalpha C library function.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-numeric?")
@deffn primitive char-numeric? chr
Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
Numeric means the same thing as the isdigit C library function.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-whitespace?")
@deffn primitive char-whitespace? chr
Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
Whitespace means the same thing as the isspace C library function.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-upper-case?")
@deffn primitive char-upper-case? chr
Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
Uppercase means the same thing as the isupper C library function.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-lower-case?")
@deffn primitive char-lower-case? chr
Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
Lowercase means the same thing as the islower C library function.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-is-both?")
@deffn primitive char-is-both? chr
Return @code{#t} iff @var{chr} is either uppercase or lowercase, else @code{#f}.
Uppercase and lowercase are as defined by the isupper and islower
C library functions.
@end deffn

@c docstring begin (texi-doc-string "guile" "char->integer")
@deffn primitive char->integer chr
Return the number corresponding to ordinal position of @var{chr} in the
ASCII sequence.
@end deffn

@c docstring begin (texi-doc-string "guile" "integer->char")
@deffn primitive integer->char n
Return the character at position @var{n} in the ASCII sequence.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-upcase")
@deffn primitive char-upcase chr
Return the uppercase character version of @var{chr}.
@end deffn

@c docstring begin (texi-doc-string "guile" "char-downcase")
@deffn primitive char-downcase chr
Return the lowercase character version of @var{chr}.
@end deffn


@node Strings
@section Strings

[FIXME: this is pasted in from Tom Lord's original guile.texi and should
be reviewed]

For the sake of efficiency, two special kinds of strings are available
in Guile: shared substrings and the misleadingly named ``read-only''
strings.  It is not necessary to know about these to program in Guile,
but you are likely to run into one or both of these special string types
eventually, and it will be helpful to know how they work.

@menu
* String Fun::                  New functions for manipulating strings.
* Shared Substrings::           Strings which share memory with each other.
* Read Only Strings::           Treating certain non-strings as strings.
@end menu

@node String Fun
@subsection String Fun

@c docstring begin (texi-doc-string "guile" "string")
@c docstring begin (texi-doc-string "guile" "list->string")
@deffn primitive string . chrs
@deffnx primitive list->string chrs
Returns a newly allocated string composed of the arguments,
@var{chrs}.
@end deffn

@c docstring begin (texi-doc-string "guile" "make-string")
@deffn primitive make-string k [chr]
Return a newly allocated string of
length @var{k}.  If @var{chr} is given, then all elements of
the string are initialized to @var{chr}, otherwise the contents
of the @var{string} are unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "string-append")
@deffn primitive string-append . args
Return a newly allocated string whose characters form the
concatenation of the given strings, @var{args}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string-length")
@deffn primitive string-length string
Return the number of characters in @var{string}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string-ref")
@deffn primitive string-ref str k
Return character @var{k} of @var{str} using zero-origin
indexing. @var{k} must be a valid index of @var{str}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string-set!")
@deffn primitive string-set! str k chr
Store @var{chr} in element @var{k} of @var{str} and return
an unspecified value. @var{k} must be a valid index of
@var{str}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string?")
@deffn primitive string? obj
Returns @code{#t} iff @var{obj} is a string, else returns
@code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "substring")
@deffn primitive substring str start [end]
Return a newly allocated string formed from the characters
of @var{str} beginning with index @var{start} (inclusive) and
ending with index @var{end} (exclusive).
@var{str} must be a string, @var{start} and @var{end} must be
exact integers satisfying:

0 <= @var{start} <= @var{end} <= (string-length @var{str}).
@end deffn

@c docstring begin (texi-doc-string "guile" "string-index")
@deffn primitive string-index str chr [frm [to]]
Return the index of the first occurrence of @var{chr} in @var{str}.  The
optional integer arguments @var{frm} and @var{to} limit the search to
a portion of the string.  This procedure essentially implements the
@code{index} or @code{strchr} functions from the C library.

(qdocs:)  Returns the index of @var{char} in @var{str}, or @code{#f} if the
@var{char} isn't in @var{str}. If @var{frm} is given and not @code{#f},
it is used as the starting index; if @var{to} is given and not @var{#f},
it is used as the ending index (exclusive).

@example
(string-index "weiner" #\e)
@result{} 1

(string-index "weiner" #\e 2)
@result{} 4

(string-index "weiner" #\e 2 4)
@result{} #f
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "string-rindex")
@deffn primitive string-rindex str chr [frm [to]]
Like @code{string-index}, but search from the right of the string rather
than from the left.  This procedure essentially implements the
@code{rindex} or @code{strrchr} functions from the C library.

(qdocs:) The same as @code{string-index}, except it gives the rightmost occurance
of @var{char} in the range [@var{frm}, @var{to}-1], which defaults to
the entire string.

@example
(string-rindex "weiner" #\e)
@result{} 4

(string-rindex "weiner" #\e 2 4)
@result{} #f

(string-rindex "weiner" #\e 2 5)
@result{} 4
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "substring-move!")
@c docstring begin (texi-doc-string "guile" "substring-move-left!")
@c docstring begin (texi-doc-string "guile" "substring-move-right!")
@deffn primitive substring-move! str1 start1 end1 str2 start2
@deffnx primitive substring-move-left! str1 start1 end1 str2 start2
@deffnx primitive substring-move-right! str1 start1 end1 str2 start2
Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
into @var{str2} beginning at position @var{end2}.
@code{substring-move-right!} begins copying from the rightmost character
and moves left, and @code{substring-move-left!} copies from the leftmost
character moving right.

It is useful to have two functions that copy in different directions so
that substrings can be copied back and forth within a single string.  If
you wish to copy text from the left-hand side of a string to the
right-hand side of the same string, and the source and destination
overlap, you must be careful to copy the rightmost characters of the
text first, to avoid clobbering your data.  Hence, when @var{str1} and
@var{str2} are the same string, you should use
@code{substring-move-right!} when moving text from left to right, and
@code{substring-move-left!}  otherwise.  If @code{str1} and @samp{str2}
are different strings, it does not matter which function you use.
@end deffn

@deffn primitive substring-move-left! str1 start1 end1 str2 start2
@end deffn
@deftypefn {C Function} SCM scm_substring_move_left_x (SCM @var{str1}, SCM @var{start1}, SCM @var{end1}, SCM @var{str2}, SCM @var{start2})
[@strong{Note:} this is only valid if you've applied the strop patch].

Moves a substring of @var{str1}, from @var{start1} to @var{end1}
(@var{end1} is exclusive), into @var{str2}, starting at
@var{start2}. Allows overlapping strings.

@example
(define x (make-string 10 #\a))
(define y "bcd")
(substring-move-left! x 2 5 y 0)
y
@result{} "aaa"

x
@result{} "aaaaaaaaaa"

(define y "bcdefg")
(substring-move-left! x 2 5 y 0)
y
@result{} "aaaefg"

(define y "abcdefg")
(substring-move-left! y 2 5 y 3)
y
@result{} "abccccg"
@end example
@end deftypefn

@deffn substring-move-right! str1 start1 end1 str2 start2
@end deffn
@deftypefn {C Function} SCM scm_substring_move_right_x (SCM @var{str1}, SCM @var{start1}, SCM @var{end1}, SCM @var{str2}, SCM @var{start2})
[@strong{Note:} this is only valid if you've applied the strop patch, if
it hasn't made it into the guile tree].

Does much the same thing as @code{substring-move-left!}, except it
starts moving at the end of the sequence, rather than the beginning.
@example
(define y "abcdefg")
(substring-move-right! y 2 5 y 0)
y
@result{} "ededefg"

(define y "abcdefg")
(substring-move-right! y 2 5 y 3)
y
@result{} "abccdeg"
@end example
@end deftypefn

@c docstring begin (texi-doc-string "guile" "vector-move-left!")
@deffn primitive vector-move-left! vec1 start1 end1 vec2 start2
Vector version of @code{substring-move-left!}.
@end deffn

@c docstring begin (texi-doc-string "guile" "vector-move-right!")
@deffn primitive vector-move-right! vec1 start1 end1 vec2 start2
Vector version of @code{substring-move-right!}.
@end deffn

@c ARGFIXME fill/fill-char
@c docstring begin (texi-doc-string "guile" "substring-fill!")
@deffn primitive substring-fill! str start end fill
Change every character in @var{str} between @var{start} and @var{end} to
@var{fill-char}.

(qdocs:) Destructively fills @var{str}, from @var{start} to @var{end}, with @var{fill}.

@example
(define y "abcdefg")
(substring-fill! y 1 3 #\r)
y
@result{} "arrdefg"
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "string-null?")
@deffn primitive string-null? str
Return @code{#t} if @var{str}'s length is nonzero, and @code{#f}
otherwise.

(qdocs:) Returns @code{#t} if @var{str} is empty, else returns @code{#f}.

@example
(string-null? "")
@result{} #t

(string-null? y)
@result{} #f
@end example
@end deffn

@c ARGFIXME v/str
@c docstring begin (texi-doc-string "guile" "string-upcase!")
@deffn primitive string-upcase! str
Destructively upcase every character in @code{str}.

(qdocs:) Converts each element in @var{str} to upper case.

@example
(string-upcase! y)
@result{} "ARRDEFG"

y
@result{} "ARRDEFG"
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "string-upcase")
@deffn primitive string-upcase str
Upcase every character in @code{str}.
@end deffn

@c ARGFIXME v/str
@c docstring begin (texi-doc-string "guile" "string-downcase!")
@deffn primitive string-downcase! str
Destructively downcase every character in @code{str}.

(qdocs:) Converts each element in @var{str} to lower case.

@example
y
@result{} "ARRDEFG"

(string-downcase! y)
@result{} "arrdefg"

y
@result{} "arrdefg"
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "string-downcase")
@deffn primitive string-downcase str
Downcase every character in @code{str}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string-capitalize!")
@deffn primitive string-capitalize! str
Destructively capitalize every character in @code{str}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string-capitalize")
@deffn primitive string-capitalize str
Capitalize every character in @code{str}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string-ci<=?")
@deffn primitive string-ci<=? s1 s2
Case insensitive lexicographic ordering predicate;
returns @t{#t} if @var{s1} is lexicographically less than
or equal to @var{s2} regardless of case.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string-ci<?")
@deffn primitive string-ci<? s1 s2
Case insensitive lexicographic ordering predicate;
returns @t{#t} if @var{s1} is lexicographically less than
@var{s2} regardless of case.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string-ci=?")
@deffn primitive string-ci=? s1 s2
Case-insensitive string equality predicate; returns @t{#t} if
the two strings are the same length and their component characters
match (ignoring case) at each position; otherwise returns @t{#f}. (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string-ci>=?")
@deffn primitive string-ci>=? s1 s2
Case insensitive lexicographic ordering predicate;
returns @t{#t} if @var{s1} is lexicographically greater than
or equal to @var{s2} regardless of case.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string-ci>?")
@deffn primitive string-ci>? s1 s2
Case insensitive lexicographic ordering predicate;
returns @t{#t} if @var{s1} is lexicographically greater than
@var{s2} regardless of case.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string<=?")
@deffn primitive string<=? s1 s2
Lexicographic ordering predicate; returns @t{#t} if @var{s1}
is lexicographically less than or equal to @var{s2}.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string<?")
@deffn primitive string<? s1 s2
Lexicographic ordering predicate; returns @t{#t} if @var{s1}
is lexicographically less than @var{s2}.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string=?")
@deffn primitive string=? s1 s2
Lexicographic equality predicate;
Returns @t{#t} if the two strings are the same length and contain the same
characters in the same positions, otherwise returns @t{#f}. (r5rs)

@samp{String-ci=?} treats
upper and lower case letters as though they were the same character, but
@samp{string=?} treats upper and lower case as distinct characters.
@end deffn

@c docstring begin (texi-doc-string "guile" "string>=?")
@deffn primitive string>=? s1 s2
Lexicographic ordering predicate; returns @t{#t} if @var{s1}
is lexicographically greater than or equal to @var{s2}.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string>?")
@deffn primitive string>? s1 s2
Lexicographic ordering predicate; returns @t{#t} if @var{s1}
is lexicographically greater than @var{s2}.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string->list")
@deffn primitive string->list str
@samp{String->list} returns a newly allocated list of the
characters that make up the given string.  @samp{List->string}
returns a newly allocated string formed from the characters in the list
@var{list}, which must be a list of characters. @samp{String->list}
and @samp{list->string} are
inverses so far as @samp{equal?} is concerned.  (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string-ci->symbol")
@deffn primitive string-ci->symbol str
Return the symbol whose name is @var{str}, downcased in necessary(???).
@end deffn

@c docstring begin (texi-doc-string "guile" "string-copy")
@deffn primitive string-copy str
Returns a newly allocated copy of the given @var{string}. (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "string-fill!")
@deffn primitive string-fill! str chr
Stores @var{char} in every element of the given @var{string} and returns an
unspecified value.  (r5rs)
@end deffn


@node Shared Substrings
@subsection Shared Substrings

Whenever you extract a substring using @code{substring}, the Scheme
interpreter allocates a new string and copies data from the old string.
This is expensive, but @code{substring} is so convenient for
manipulating text that programmers use it often.

Guile Scheme provides the concept of the @dfn{shared substring} to
improve performance of many substring-related operations.  A shared
substring is an object that mostly behaves just like an ordinary
substring, except that it actually shares storage space with its parent
string.

@c ARGFIXME frm/start to/end
@c docstring begin (texi-doc-string "guile" "make-shared-substring")
@deffn primitive make-shared-substring str [frm [to]]
Return a shared substring of @var{str}.  The semantics are the same as
for the @code{substring} function: the shared substring returned
includes all of the text from @var{str} between indexes @var{start}
(inclusive) and @var{end} (exclusive).  If @var{end} is omitted, it
defaults to the end of @var{str}.  The shared substring returned by
@code{make-shared-substring} occupies the same storage space as
@var{str}.
@end deffn

Example:

@example
(define foo "the quick brown fox")
(define bar (make-shared-substring some-string 4 9))

foo => "t h e   q u i c k   b r o w n   f o x"
bar =========> |---------|
@end example

The shared substring @var{bar} is not given its own storage space.
Instead, the Guile interpreter notes internally that @var{bar} points to
a portion of the memory allocated to @var{foo}.  However, @var{bar}
behaves like an ordinary string in most respects: it may be used with
string primitives like @code{string-length}, @code{string-ref},
@code{string=?}.  Guile makes the necessary translation between indices
of @var{bar} and indices of @var{foo} automatically.

@example
(string-length? bar) @result{} 5	; bar only extends from indices 4 to 9
(string-ref bar 3)  @result{} #\c	; same as (string-ref foo 7)
(make-shared-substring bar 2)
  @result{} "ick"			; can even make a shared substring!
@end example

Because creating a shared substring does not require allocating new
storage from the heap, it is a very fast operation.  However, because it
shares memory with its parent string, a change to the contents of the
parent string will implicitly change the contents of its shared
substrings.

@example
(string-set! foo 7 #\r)
bar @result{} "quirk"
@end example

Guile considers shared substrings to be immutable.  This is because
programmers might not always be aware that a given string is really a
shared substring, and might innocently try to mutate it without
realizing that the change would affect its parent string.  (We are
currently considering a "copy-on-write" strategy that would permit
modifying shared substrings without affecting the parent string.)

In general, shared substrings are useful in circumstances where it is
important to divide a string into smaller portions, but you do not
expect to change the contents of any of the strings involved.

@node Read Only Strings
@subsection Read Only Strings

Type-checking in Guile primitives distinguishes between mutable strings
and read only strings.  Mutable strings answer @code{#t} to
@code{string?}  while read only strings may or may not.   All kinds of
strings, whether or not they are mutable return #t to this:

@c ARGFIXME x/obj
@c docstring begin (texi-doc-string "guile" "read-only-string?")
@deffn primitive read-only-string? obj
Return true if @var{obj} can be read as a string,

This illustrates the difference between @code{string?} and
@code{read-only-string?}:

@example
(string? "a string") @result{} #t
(string? 'a-symbol) @result{} #f

(read-only-string? "a string") @result{} #t
(read-only-string? 'a-symbol) @result{} #t
@end example
@end deffn

"Read-only" refers to how the string will be used, not how the string is
permitted to be used.  In particular, all strings are "read-only
strings" even if they are mutable, because a function that only reads
from a string can certainly operate on even a mutable string.

Symbols are an example of read-only strings.  Many string functions,
such as @code{string-append} are happy to operate on symbols.  Many
functions that expect a string argument, such as @code{open-file}, will
accept a symbol as well.

Shared substrings, discussed in the previous chapter, also happen to be
read-only strings.


@node Regular Expressions
@section Regular Expressions

@cindex regular expressions
@cindex regex
@cindex emacs regexp

A @dfn{regular expression} (or @dfn{regexp}) is a pattern that
describes a whole class of strings.  A full description of regular
expressions and their syntax is beyond the scope of this manual;
an introduction can be found in the Emacs manual (@pxref{Regexps,
, Syntax of Regular Expressions, emacs, The GNU Emacs Manual}, or
in many general Unix reference books.

If your system does not include a POSIX regular expression library, and
you have not linked Guile with a third-party regexp library such as Rx,
these functions will not be available.  You can tell whether your Guile
installation includes regular expression support by checking whether the
@code{*features*} list includes the @code{regex} symbol.

@menu
* Regexp Functions::            Functions that create and match regexps.
* Match Structures::            Finding what was matched by a regexp.
* Backslash Escapes::           Removing the special meaning of regexp metacharacters.
* Rx Interface::                Tom Lord's Rx library does things differently.
@end menu

[FIXME: it may be useful to include an Examples section.  Parts of this
interface are bewildering on first glance.]

@node Regexp Functions
@subsection Regexp Functions

By default, Guile supports POSIX extended regular expressions.
That means that the characters @samp{(}, @samp{)}, @samp{+} and
@samp{?} are special, and must be escaped if you wish to match the
literal characters.

This regular expression interface was modeled after that
implemented by SCSH, the Scheme Shell.  It is intended to be
upwardly compatible with SCSH regular expressions.

@c begin (scm-doc-string "regex.scm" "string-match")
@deffn procedure string-match pattern str [start]
Compile the string @var{pattern} into a regular expression and compare
it with @var{str}.  The optional numeric argument @var{start} specifies
the position of @var{str} at which to begin matching.

@code{string-match} returns a @dfn{match structure} which
describes what, if anything, was matched by the regular
expression.  @xref{Match Structures}.  If @var{str} does not match
@var{pattern} at all, @code{string-match} returns @code{#f}.
@end deffn

Each time @code{string-match} is called, it must compile its
@var{pattern} argument into a regular expression structure.  This
operation is expensive, which makes @code{string-match} inefficient if
the same regular expression is used several times (for example, in a
loop).  For better performance, you can compile a regular expression in
advance and then match strings against the compiled regexp.

@c ARGFIXME pat/str flags/flag
@c docstring begin (texi-doc-string "guile" "make-regexp")
@deffn primitive make-regexp pat . flags
Compile the regular expression described by @var{str}, and return the
compiled regexp structure.  If @var{str} does not describe a legal
regular expression, @code{make-regexp} throws a
@code{regular-expression-syntax} error.

The @var{flag} arguments change the behavior of the compiled regexp.
The following flags may be supplied:

@table @code
@item regexp/icase
Consider uppercase and lowercase letters to be the same when matching.

@item regexp/newline
If a newline appears in the target string, then permit the @samp{^} and
@samp{$} operators to match immediately after or immediately before the
newline, respectively.  Also, the @samp{.} and @samp{[^...]} operators
will never match a newline character.  The intent of this flag is to
treat the target string as a buffer containing many lines of text, and
the regular expression as a pattern that may match a single one of those
lines.

@item regexp/basic
Compile a basic (``obsolete'') regexp instead of the extended
(``modern'') regexps that are the default.  Basic regexps do not
consider @samp{|}, @samp{+} or @samp{?} to be special characters, and
require the @samp{@{...@}} and @samp{(...)} metacharacters to be
backslash-escaped (@pxref{Backslash Escapes}).  There are several other
differences between basic and extended regular expressions, but these
are the most significant.

@item regexp/extended
Compile an extended regular expression rather than a basic regexp.  This
is the default behavior; this flag will not usually be needed.  If a
call to @code{make-regexp} includes both @code{regexp/basic} and
@code{regexp/extended} flags, the one which comes last will override
the earlier one.
@end table
@end deffn

@c ARGFIXME rx/regexp
@c docstring begin (texi-doc-string "guile" "regexp-exec")
@deffn primitive regexp-exec rx str [start [flags]]
Match the compiled regular expression @var{regexp} against @code{str}.
If the optional integer @var{start} argument is provided, begin matching
from that position in the string.  Return a match structure describing
the results of the match, or @code{#f} if no match could be found.
@end deffn

@c ARGFIXME x/obj
@c docstring begin (texi-doc-string "guile" "regexp?")
@deffn primitive regexp? x
Return @code{#t} if @var{obj} is a compiled regular expression, or
@code{#f} otherwise.
@end deffn

Regular expressions are commonly used to find patterns in one string and
replace them with the contents of another string.

@c begin (scm-doc-string "regex.scm" "regexp-substitute")
@deffn procedure regexp-substitute port match [item@dots{}]
Write to the output port @var{port} selected contents of the match
structure @var{match}.  Each @var{item} specifies what should be
written, and may be one of the following arguments:

@itemize @bullet
@item
A string.  String arguments are written out verbatim.

@item
An integer.  The submatch with that number is written.

@item
The symbol @samp{pre}.  The portion of the matched string preceding
the regexp match is written.

@item
The symbol @samp{post}.  The portion of the matched string following
the regexp match is written.
@end itemize

@var{port} may be @code{#f}, in which case nothing is written; instead,
@code{regexp-substitute} constructs a string from the specified
@var{item}s and returns that.
@end deffn

@c begin (scm-doc-string "regex.scm" "regexp-substitute")
@deffn procedure regexp-substitute/global port regexp target [item@dots{}]
Similar to @code{regexp-substitute}, but can be used to perform global
substitutions on @var{str}.  Instead of taking a match structure as an
argument, @code{regexp-substitute/global} takes two string arguments: a
@var{regexp} string describing a regular expression, and a @var{target}
string which should be matched against this regular expression.

Each @var{item} behaves as in @var{regexp-substitute}, with the
following exceptions:

@itemize @bullet
@item
A function may be supplied.  When this function is called, it will be
passed one argument: a match structure for a given regular expression
match.  It should return a string to be written out to @var{port}.

@item
The @samp{post} symbol causes @code{regexp-substitute/global} to recurse
on the unmatched portion of @var{str}.  This @emph{must} be supplied in
order to perform global search-and-replace on @var{str}; if it is not
present among the @var{item}s, then @code{regexp-substitute/global} will
return after processing a single match.
@end itemize
@end deffn

@node Match Structures
@subsection Match Structures

@cindex match structures

A @dfn{match structure} is the object returned by @code{string-match} and
@code{regexp-exec}.  It describes which portion of a string, if any,
matched the given regular expression.  Match structures include: a
reference to the string that was checked for matches; the starting and
ending positions of the regexp match; and, if the regexp included any
parenthesized subexpressions, the starting and ending positions of each
submatch.

In each of the regexp match functions described below, the @code{match}
argument must be a match structure returned by a previous call to
@code{string-match} or @code{regexp-exec}.  Most of these functions
return some information about the original target string that was
matched against a regular expression; we will call that string
@var{target} for easy reference.

@c begin (scm-doc-string "regex.scm" "regexp-match?")
@deffn procedure regexp-match? obj
Return @code{#t} if @var{obj} is a match structure returned by a
previous call to @code{regexp-exec}, or @code{#f} otherwise.
@end deffn

@c begin (scm-doc-string "regex.scm" "match:substring")
@deffn procedure match:substring match [n]
Return the portion of @var{target} matched by subexpression number
@var{n}.  Submatch 0 (the default) represents the entire regexp match.
If the regular expression as a whole matched, but the subexpression
number @var{n} did not match, return @code{#f}.
@end deffn

@c begin (scm-doc-string "regex.scm" "match:start")
@deffn procedure match:start match [n]
Return the starting position of submatch number @var{n}.
@end deffn

@c begin (scm-doc-string "regex.scm" "match:end")
@deffn procedure match:end match [n]
Return the ending position of submatch number @var{n}.
@end deffn

@c begin (scm-doc-string "regex.scm" "match:prefix")
@deffn procedure match:prefix match
Return the unmatched portion of @var{target} preceding the regexp match.
@end deffn

@c begin (scm-doc-string "regex.scm" "match:suffix")
@deffn procedure match:suffix match
Return the unmatched portion of @var{target} following the regexp match.
@end deffn

@c begin (scm-doc-string "regex.scm" "match:count")
@deffn procedure match:count match
Return the number of parenthesized subexpressions from @var{match}.
Note that the entire regular expression match itself counts as a
subexpression, and failed submatches are included in the count.
@end deffn

@c begin (scm-doc-string "regex.scm" "match:string")
@deffn procedure match:string match
Return the original @var{target} string.
@end deffn

@node Backslash Escapes
@subsection Backslash Escapes

Sometimes you will want a regexp to match characters like @samp{*} or
@samp{$} exactly.  For example, to check whether a particular string
represents a menu entry from an Info node, it would be useful to match
it against a regexp like @samp{^* [^:]*::}.  However, this won't work;
because the asterisk is a metacharacter, it won't match the @samp{*} at
the beginning of the string.  In this case, we want to make the first
asterisk un-magic.

You can do this by preceding the metacharacter with a backslash
character @samp{\}.  (This is also called @dfn{quoting} the
metacharacter, and is known as a @dfn{backslash escape}.)  When Guile
sees a backslash in a regular expression, it considers the following
glyph to be an ordinary character, no matter what special meaning it
would ordinarily have.  Therefore, we can make the above example work by
changing the regexp to @samp{^\* [^:]*::}.  The @samp{\*} sequence tells
the regular expression engine to match only a single asterisk in the
target string.

Since the backslash is itself a metacharacter, you may force a regexp to
match a backslash in the target string by preceding the backslash with
itself.  For example, to find variable references in a @TeX{} program,
you might want to find occurrences of the string @samp{\let\} followed
by any number of alphabetic characters.  The regular expression
@samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the
regexp each match a single backslash in the target string.

@c begin (scm-doc-string "regex.scm" "regexp-quote")
@deffn procedure regexp-quote str
Quote each special character found in @var{str} with a backslash, and
return the resulting string.
@end deffn

@strong{Very important:} Using backslash escapes in Guile source code
(as in Emacs Lisp or C) can be tricky, because the backslash character
has special meaning for the Guile reader.  For example, if Guile
encounters the character sequence @samp{\n} in the middle of a string
while processing Scheme code, it replaces those characters with a
newline character.  Similarly, the character sequence @samp{\t} is
replaced by a horizontal tab.  Several of these @dfn{escape sequences}
are processed by the Guile reader before your code is executed.
Unrecognized escape sequences are ignored: if the characters @samp{\*}
appear in a string, they will be translated to the single character
@samp{*}.

This translation is obviously undesirable for regular expressions, since
we want to be able to include backslashes in a string in order to
escape regexp metacharacters.  Therefore, to make sure that a backslash
is preserved in a string in your Guile program, you must use @emph{two}
consecutive backslashes:

@lisp
(define Info-menu-entry-pattern (make-regexp "^\\* [^:]*"))
@end lisp

The string in this example is preprocessed by the Guile reader before
any code is executed.  The resulting argument to @code{make-regexp} is
the string @samp{^\* [^:]*}, which is what we really want.

This also means that in order to write a regular expression that matches
a single backslash character, the regular expression string in the
source code must include @emph{four} backslashes.  Each consecutive pair
of backslashes gets translated by the Guile reader to a single
backslash, and the resulting double-backslash is interpreted by the
regexp engine as matching a single backslash character.  Hence:

@lisp
(define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*"))
@end lisp

The reason for the unwieldiness of this syntax is historical.  Both
regular expression pattern matchers and Unix string processing systems
have traditionally used backslashes with the special meanings
described above.  The POSIX regular expression specification and ANSI C
standard both require these semantics.  Attempting to abandon either
convention would cause other kinds of compatibility problems, possibly
more severe ones.  Therefore, without extending the Scheme reader to
support strings with different quoting conventions (an ungainly and
confusing extension when implemented in other languages), we must adhere
to this cumbersome escape syntax.

@node Rx Interface
@subsection Rx Interface

[FIXME: this is taken from Gary and Mark's quick summaries and should be
reviewed and expanded.  Rx is pretty stable, so could already be done!]

@cindex rx
@cindex finite automaton

Guile includes an interface to Tom Lord's Rx library (currently only to
POSIX regular expressions).  Use of the library requires a two step
process: compile a regular expression into an efficient structure, then
use the structure in any number of string comparisons.

For example, given the
regular expression @samp{abc.} (which matches any string containing
@samp{abc} followed by any single character):

@smalllisp
guile> @kbd{(define r (regcomp "abc."))}
guile> @kbd{r}
#<rgx abc.>
guile> @kbd{(regexec r "abc")}
#f
guile> @kbd{(regexec r "abcd")}
#((0 . 4))
guile>
@end smalllisp

The definitions of @code{regcomp} and @code{regexec} are as follows:

@c NJFIXME not in libguile!
@deffn primitive regcomp pattern [flags]
Compile the regular expression pattern using POSIX rules.  Flags is
optional and should be specified using symbolic names:
@defvar REG_EXTENDED
use extended POSIX syntax
@end defvar
@defvar REG_ICASE
use case-insensitive matching
@end defvar
@defvar REG_NEWLINE
allow anchors to match after newline characters in the
string and prevents @code{.} or @code{[^...]} from matching newlines.
@end defvar

The @code{logior} procedure can be used to combine multiple flags.
The default is to use
POSIX basic syntax, which makes @code{+} and @code{?}  literals and @code{\+}
and @code{\?}
operators.  Backslashes in @var{pattern} must be escaped if specified in a
literal string e.g., @code{"\\(a\\)\\?"}.
@end deffn

@c NJFIXME not in libguile!
@deffn primitive regexec regex string [match-pick] [flags]

Match @var{string} against the compiled POSIX regular expression
@var{regex}.
@var{match-pick} and @var{flags} are optional.  Possible flags (which can be
combined using the logior procedure) are:

@defvar REG_NOTBOL
The beginning of line operator won't match the beginning of
@var{string} (presumably because it's not the beginning of a line)
@end defvar

@defvar REG_NOTEOL
Similar to REG_NOTBOL, but prevents the end of line operator
from matching the end of @var{string}.
@end defvar

If no match is possible, regexec returns #f.  Otherwise @var{match-pick}
determines the return value:

@code{#t} or unspecified: a newly-allocated vector is returned,
containing pairs with the indices of the matched part of @var{string} and any
substrings.

@code{""}: a list is returned: the first element contains a nested list
with the matched part of @var{string} surrounded by the the unmatched parts.
Remaining elements are matched substrings (if any).  All returned
substrings share memory with @var{string}.

@code{#f}: regexec returns #t if a match is made, otherwise #f.

vector: the supplied vector is returned, with the first element replaced
by a pair containing the indices of the matched portion of @var{string} and
further elements replaced by pairs containing the indices of matched
substrings (if any).

list: a list will be returned, with each member of the list
specified by a code in the corresponding position of the supplied list:

a number: the numbered matching substring (0 for the entire match).

@code{#\<}: the beginning of @var{string} to the beginning of the part matched
by regex.

@code{#\>}: the end of the matched part of @var{string} to the end of
@var{string}.

@code{#\c}: the "final tag", which seems to be associated with the "cut
operator", which doesn't seem to be available through the posix
interface.

e.g., @code{(list #\< 0 1 #\>)}.  The returned substrings share memory with
@var{string}.
@end deffn

Here are some other procedures that might be used when using regular
expressions:

@c NJFIXME not in libguile!
@deffn primitive compiled-regexp? obj
Test whether obj is a compiled regular expression.
@end deffn

@c NJFIXME not in libguile!
@deffn primitive regexp->dfa regex [flags]
@end deffn

@c NJFIXME not in libguile!
@deffn primitive dfa-fork dfa
@end deffn

@c NJFIXME not in libguile!
@deffn primitive reset-dfa! dfa
@end deffn

@c NJFIXME not in libguile!
@deffn primitive dfa-final-tag dfa
@end deffn

@c NJFIXME not in libguile!
@deffn primitive dfa-continuable? dfa
@end deffn

@c NJFIXME not in libguile!
@deffn primitive advance-dfa! dfa string
@end deffn


@node Symbols and Variables
@section Symbols and Variables

Guile symbol tables are hash tables.  Each hash table, also called an
@dfn{obarray} (for `object array'), is a vector of association lists.
Each entry in the alists is a pair (@var{SYMBOL} . @var{VALUE}).  To
@dfn{intern} a symbol in a symbol table means to return its
(@var{SYMBOL} . @var{VALUE}) pair, adding a new entry to the symbol
table (with an undefined value) if none is yet present.

@c docstring begin (texi-doc-string "guile" "builtin-bindings")
@deffn primitive builtin-bindings
Create and return a copy of the global symbol table, removing all
unbound symbols.
@end deffn

@c docstring begin (texi-doc-string "guile" "gensym")
@deffn primitive gensym [prefix]
Create a new symbol with a name constructed from a prefix and
a counter value. The string @var{prefix} can be specified as
an optional argument. Default prefix is @code{g}.  The counter
is increased by 1 at each call. There is no provision for
resetting the counter.
@end deffn

@c docstring begin (texi-doc-string "guile" "gentemp")
@deffn primitive gentemp [prefix [obarray]]
Create a new symbol with a name unique in an obarray.
The name is constructed from an optional string @var{prefix}
and a counter value.  The default prefix is @code{t}.  The
@var{obarray} is specified as a second optional argument.
Default is the system obarray where all normal symbols are
interned.  The counter is increased by 1 at each
call.  There is no provision for resetting the counter.
@end deffn

@c docstring begin (texi-doc-string "guile" "intern-symbol")
@deffn primitive intern-symbol obarray string
Add a new symbol to @var{obarray} with name @var{string}, bound to an
unspecified initial value.  The symbol table is not modified if a symbol
with this name is already present.
@end deffn

@c docstring begin (texi-doc-string "guile" "string->obarray-symbol")
@deffn primitive string->obarray-symbol obarray string [soft?]
Intern a new symbol in @var{obarray}, a symbol table, with name
@var{string}.

If @var{obarray} is @code{#f}, use the default system symbol table.  If
@var{obarray} is @code{#t}, the symbol should not be interned in any
symbol table; merely return the pair (@var{symbol}
. @var{#<undefined>}).

The @var{soft?} argument determines whether new symbol table entries
should be created when the specified symbol is not already present in
@var{obarray}.  If @var{soft?} is specified and is a true value, then
new entries should not be added for symbols not already present in the
table; instead, simply return @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "string->symbol")
@deffn primitive string->symbol string
Returns the symbol whose name is @var{string}.  This procedure can
create symbols with names containing special characters or letters in
the non-standard case, but it is usually a bad idea to create such
symbols because in some implementations of Scheme they cannot be read as
themselves.  See @samp{symbol->string}.

The following examples assume that the implementation's standard case is
lower case:

@format
@t{(eq? 'mISSISSIppi 'mississippi)
          ==>  #t
(string->symbol "mISSISSIppi")
          ==>
  @r{}the symbol with name "mISSISSIppi"
(eq? 'bitBlt (string->symbol "bitBlt"))
          ==>  #f
(eq? 'JollyWog
     (string->symbol
       (symbol->string 'JollyWog)))
          ==>  #t
(string=? "K. Harper, M.D."
          (symbol->string
            (string->symbol "K. Harper, M.D.")))
          ==>  #t
}
@end format
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol->string")
@deffn primitive symbol->string symbol
Returns the name of @var{symbol} as a string.  If the symbol was part of
an object returned as the value of a literal expression (section
@pxref{Literal expressions,,,r4rs, The Revised^4 Report on Scheme}) or
by a call to the @samp{read} procedure, and its name contains alphabetic
characters, then the string returned will contain characters in the
implementation's preferred standard case---some implementations will
prefer upper case, others lower case.  If the symbol was returned by
@samp{string->symbol}, the case of characters in the string returned
will be the same as the case in the string that was passed to
@samp{string->symbol}.  It is an error to apply mutation procedures like
@code{string-set!} to strings returned by this procedure. (r5rs)

The following examples assume that the implementation's standard case is
lower case:

@format
@t{(symbol->string 'flying-fish)
                                ==>  "flying-fish"
(symbol->string 'Martin)               ==>  "martin"
(symbol->string
   (string->symbol "Malvina"))
                           ==>  "Malvina"
}
@end format
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-binding")
@deffn primitive symbol-binding obarray string
Look up in @var{obarray} the symbol whose name is @var{string}, and
return the value to which it is bound.  If @var{obarray} is @code{#f},
use the global symbol table.  If @var{string} is not interned in
@var{obarray}, an error is signalled.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-bound?")
@deffn primitive symbol-bound? obarray string
Return @var{#t} if @var{obarray} contains a symbol with name
@var{string} bound to a defined value.  This differs from
@var{symbol-interned?} in that the mere mention of a symbol usually causes
it to be interned; @code{symbol-bound?} determines whether a symbol has
been given any meaningful value.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-fref")
@deffn primitive symbol-fref symbol
Return the contents of @var{symbol}'s @dfn{function slot}.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-fset!")
@deffn primitive symbol-fset! symbol value
Change the binding of @var{symbol}'s function slot.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-hash")
@deffn primitive symbol-hash symbol
Return a hash value for @var{symbol}.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-interned?")
@deffn primitive symbol-interned? obarray string
Return @var{#t} if @var{obarray} contains a symbol with name
@var{string}, and @var{#f} otherwise.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-pref")
@deffn primitive symbol-pref symbol
Return the @dfn{property list} currently associated with @var{symbol}.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-pset!")
@deffn primitive symbol-pset! symbol value
Change the binding of @var{symbol}'s property slot.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol-set!")
@deffn primitive symbol-set! obarray string value
Find the symbol in @var{obarray} whose name is @var{string}, and rebind
it to @var{value}.  An error is signalled if @var{string} is not present
in @var{obarray}.
@end deffn

@c docstring begin (texi-doc-string "guile" "symbol?")
@deffn primitive symbol? obj
Returns @t{#t} if @var{obj} is a symbol, otherwise returns @t{#f}. (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "unintern-symbol")
@deffn primitive unintern-symbol obarray string
Remove the symbol with name @var{string} from @var{obarray}.  This
function returns @code{#t} if the symbol was present and @code{#f}
otherwise.
@end deffn

@c docstring begin (texi-doc-string "guile" "builtin-variable")
@deffn primitive builtin-variable name
Return the built-in variable with the name @var{name}.
@var{name} must be a symbol (not a string).
Then use @code{variable-ref} to access its value.
@end deffn

@c docstring begin (texi-doc-string "guile" "make-undefined-variable")
@deffn primitive make-undefined-variable [name-hint]
Return a variable object initialized to an undefined value.
If given, uses @var{name-hint} as its internal (debugging)
name, otherwise just treat it as an anonymous variable.
Remember, of course, that multiple bindings to the same
variable may exist, so @var{name-hint} is just that---a hint.
@end deffn

@c docstring begin (texi-doc-string "guile" "make-variable")
@deffn primitive make-variable init [name-hint]
Return a variable object initialized to value @var{init}.
If given, uses @var{name-hint} as its internal (debugging)
name, otherwise just treat it as an anonymous variable.
Remember, of course, that multiple bindings to the same
variable may exist, so @var{name-hint} is just that---a hint.
@end deffn

@c docstring begin (texi-doc-string "guile" "variable-bound?")
@deffn primitive variable-bound? var
Return @code{#t} iff @var{var} is bound to a value.
Throws an error if @var{var} is not a variable object.
@end deffn

@c docstring begin (texi-doc-string "guile" "variable-ref")
@deffn primitive variable-ref var
Dereference @var{var} and return its value.
@var{var} must be a variable object; see @code{make-variable}
and @code{make-undefined-variable}.
@end deffn

@c docstring begin (texi-doc-string "guile" "variable-set!")
@deffn primitive variable-set! var val
Set the value of the variable @var{var} to @var{val}.
@var{var} must be a variable object, @var{val} can be any
value. Return an unspecified value.
@end deffn

@c docstring begin (texi-doc-string "guile" "variable?")
@deffn primitive variable? obj
Return @code{#t} iff @var{obj} is a variable object, else
return @code{#f}
@end deffn


@node Keywords
@section Keywords

Keywords are self-evaluating objects with a convenient read syntax that
makes them easy to type.

Guile's keyword support conforms to R4RS, and adds a (switchable) read
syntax extension to permit keywords to begin with @code{:} as well as
@code{#:}.

@menu
* Why Use Keywords?::
* Coding With Keywords::
* Keyword Read Syntax::
* Keyword Primitives::
@end menu

@node Why Use Keywords?
@subsection Why Use Keywords?

Keywords are useful in contexts where a program or procedure wants to be
able to accept a large number of optional arguments without making its
interface unmanageable.

To illustrate this, consider a hypothetical @code{make-window}
procedure, which creates a new window on the screen for drawing into
using some graphical toolkit.  There are many parameters that the caller
might like to specify, but which could also be sensibly defaulted, for
example:

@itemize @bullet
@item
colour depth -- Default: the colour depth for the screen

@item
background colour -- Default: white

@item
width -- Default: 600

@item
height -- Default: 400
@end itemize

If @code{make-window} did not use keywords, the caller would have to
pass in a value for each possible argument, remembering the correct
argument order and using a special value to indicate the default value
for that argument:

@lisp
(make-window 'default              ;; Colour depth
             'default              ;; Background colour
             800                   ;; Width
             100                   ;; Height
             @dots{})                  ;; More make-window arguments
@end lisp

With keywords, on the other hand, defaulted arguments are omitted, and
non-default arguments are clearly tagged by the appropriate keyword.  As
a result, the invocation becomes much clearer:

@lisp
(make-window #:width 800 #:height 100)
@end lisp

On the other hand, for a simpler procedure with few arguments, the use
of keywords would be a hindrance rather than a help.  The primitive
procedure @code{cons}, for example, would not be improved if it had to
be invoked as

@lisp
(cons #:car x #:cdr y)
@end lisp

So the decision whether to use keywords or not is purely pragmatic: use
them if they will clarify the procedure invocation at point of call.

@node Coding With Keywords
@subsection Coding With Keywords

If a procedure wants to support keywords, it should take a rest argument
and then use whatever means is convenient to extract keywords and their
corresponding arguments from the contents of that rest argument.

The following example illustrates the principle: the code for
@code{make-window} uses a helper procedure called
@code{get-keyword-value} to extract individual keyword arguments from
the rest argument.

@lisp
(define (get-keyword-value args keyword default)
  (let ((kv (memq keyword args)))
    (if (and kv (>= (length kv) 2))
        (cadr kv)
        default)))

(define (make-window . args)
  (let ((depth  (get-keyword-value args #:depth  screen-depth))
        (bg     (get-keyword-value args #:bg     "white"))
        (width  (get-keyword-value args #:width  800))
        (height (get-keyword-value args #:height 100))
        @dots{})
    @dots{}))
@end lisp

But you don't need to write @code{get-keyword-value}.  The @code{(ice-9
optargs)} module provides a set of powerful macros that you can use to
implement keyword-supporting procedures like this:

@lisp
(use-modules (ice-9 optargs))

(define (make-window . args)
  (let-keywords args #f ((depth  screen-depth)
                         (bg     "white")
                         (width  800)
                         (height 100))
    ...))
@end lisp

@noindent
Or, even more economically, like this:

@lisp
(use-modules (ice-9 optargs))

(define* (make-window #:key (depth  screen-depth)
                            (bg     "white")
                            (width  800)
                            (height 100))
  ...)
@end lisp

For further details on @code{let-keywords}, @code{define*} and other
facilities provided by the @code{(ice-9 optargs)} module, @ref{Optional
Arguments}.


@node Keyword Read Syntax
@subsection Keyword Read Syntax

Guile, by default, only recognizes the keyword syntax specified by R5RS.
A token of the form @code{#:NAME}, where @code{NAME} has the same syntax
as a Scheme symbol, is the external representation of the keyword named
@code{NAME}.  Keyword objects print using this syntax as well, so values
containing keyword objects can be read back into Guile.  When used in an
expression, keywords are self-quoting objects.

If the @code{keyword} read option is set to @code{'prefix}, Guile also
recognizes the alternative read syntax @code{:NAME}.  Otherwise, tokens
of the form @code{:NAME} are read as symbols, as required by R4RS.

To enable and disable the alternative non-R4RS keyword syntax, you use
the @code{read-options} procedure documented in @ref{General option
interface} and @ref{Reader options}.

@smalllisp
(read-set! keywords 'prefix)

#:type
@result{}
#:type

:type
@result{}
#:type

(read-set! keywords #f)

#:type
@result{}
#:type

:type
@result{}
ERROR: In expression :type:
ERROR: Unbound variable: :type
ABORT: (unbound-variable)
@end smalllisp

@node Keyword Primitives
@subsection Keyword Primitives

Internally, a keyword is implemented as something like a tagged symbol,
where the tag identifies the keyword as being self-evaluating, and the
symbol, known as the keyword's @dfn{dash symbol} has the same name as
the keyword name but prefixed by a single dash.  For example, the
keyword @code{#:name} has the corresponding dash symbol @code{-name}.

Most keyword objects are constructed automatically by the reader when it
reads a token beginning with @code{#:}.  However, if you need to
construct a keyword object programmatically, you can do so by calling
@code{make-keyword-from-dash-symbol} with the corresponding dash symbol
(as the reader does).  The dash symbol for a keyword object can be
retrieved using the @code{keyword-dash-symbol} procedure.

@c docstring begin (texi-doc-string "guile" "make-keyword-from-dash-symbol")
@deffn primitive make-keyword-from-dash-symbol symbol
Make a keyword object from a @var{symbol} that starts with a dash.
@end deffn

@c docstring begin (texi-doc-string "guile" "keyword?")
@deffn primitive keyword? obj
Returns @code{#t} if the argument @var{obj} is a keyword, else @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "keyword-dash-symbol")
@deffn primitive keyword-dash-symbol keyword
Return the dash symbol for @var{keyword}.
This is the inverse of @code{make-keyword-from-dash-symbol}.
@end deffn


@node Pairs
@section Pairs

@c docstring begin (texi-doc-string "guile" "cons")
@deffn primitive cons x y
Returns a newly allocated pair whose car is @var{x} and whose cdr is
@var{y}.  The pair is guaranteed to be different (in the sense of
@code{eqv?}) from every previously existing object.
@end deffn

@c docstring begin (texi-doc-string "guile" "pair?")
@deffn primitive pair? x
Returns @code{#t} if @var{x} is a pair; otherwise returns @code{#f}.
@end deffn

@c docstring begin (texi-doc-string "guile" "set-car!")
@deffn primitive set-car! pair value
Stores @var{value} in the car field of @var{pair}.  The value returned
by @code{set-car!} is unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "set-cdr!")
@deffn primitive set-cdr! pair value
Stores @var{value} in the cdr field of @var{pair}.  The value returned
by @code{set-cdr!} is unspecified.
@end deffn


@node Lists
@section Lists

@c docstring begin (texi-doc-string "guile" "list")
@deffn primitive list . objs
Return a list containing OBJS, the arguments to `list'.
@end deffn

@c docstring begin (texi-doc-string "guile" "cons*")
@deffn primitive cons* arg . rest
@deffnx primitive list* arg . rest
Like `list', but the last arg provides the tail of the constructed list,
returning (cons ARG1 (cons ARG2 (cons ... ARGn))).
Requires at least one argument.  If given one argument, that argument
is returned as result.
This function is called `list*' in some other Schemes and in Common LISP.
@end deffn

@c docstring begin (texi-doc-string "guile" "list?")
@deffn primitive list? x
Return #t iff X is a proper list, else #f.
@end deffn

@c docstring begin (texi-doc-string "guile" "null?")
@deffn primitive null? x
Return #t iff X is the empty list, else #f.
@end deffn

@c docstring begin (texi-doc-string "guile" "length")
@deffn primitive length lst
Return the number of elements in list LST.
@end deffn

@c docstring begin (texi-doc-string "guile" "append")
@deffn primitive append . args
Returns a list consisting of the elements of the first LIST
followed by the elements of the other LISTs.

@example
  (append '(x) '(y))          =>  (x y)
  (append '(a) '(b c d))      =>  (a b c d)
  (append '(a (b)) '((c)))    =>  (a (b) (c))
@end example

The resulting list is always newly allocated, except that it shares
structure with the last LIST argument.  The last argument may
actually be any object; an improper list results if the last
argument is not a proper list.

@example
  (append '(a b) '(c . d))    =>  (a b c . d)
  (append '() 'a)             =>  a
@end example
@end deffn

@c ARGFIXME args ?
@c docstring begin (texi-doc-string "guile" "append!")
@deffn primitive append! . args
A destructive version of @code{append} (@pxref{Pairs and Lists,,,r4rs,
The Revised^4 Report on Scheme}).  The cdr field of each list's final
pair is changed to point to the head of the next list, so no consing is
performed.  Return a pointer to the mutated list.
@end deffn

@c docstring begin (texi-doc-string "guile" "last-pair")
@deffn primitive last-pair lst
Return a pointer to the last pair in @var{lst}, signalling an error if
@var{lst} is circular.
@end deffn

@c docstring begin (texi-doc-string "guile" "reverse")
@deffn primitive reverse lst
Return a new list that contains the elements of LST but in reverse order.
@end deffn

@c NJFIXME explain new_tail
@c docstring begin (texi-doc-string "guile" "reverse!")
@deffn primitive reverse! lst [new_tail]
A destructive version of @code{reverse} (@pxref{Pairs and Lists,,,r4rs,
The Revised^4 Report on Scheme}).  The cdr of each cell in @var{lst} is
modified to point to the previous list element.  Return a pointer to the
head of the reversed list.

Caveat: because the list is modified in place, the tail of the original
list now becomes its head, and the head of the original list now becomes
the tail.  Therefore, the @var{lst} symbol to which the head of the
original list was bound now points to the tail.  To ensure that the head
of the modified list is not lost, it is wise to save the return value of
@code{reverse!}
@end deffn

@c docstring begin (texi-doc-string "guile" "list-ref")
@deffn primitive list-ref list k
Return the Kth element from LIST.
@end deffn

@c docstring begin (texi-doc-string "guile" "list-set!")
@deffn primitive list-set! list k val
Set the @var{k}th element of @var{list} to @var{val}.
@end deffn

@c docstring begin (texi-doc-string "guile" "list-tail")
@c docstring begin (texi-doc-string "guile" "list-cdr-ref")
@deffn primitive list-tail lst k
@deffnx primitive list-cdr-ref lst k
Return the "tail" of @var{lst} beginning with its @var{k}th element.
The first element of the list is considered to be element 0.

@code{list-tail} and @code{list-cdr-ref} are identical.  It may help to
think of @code{list-cdr-ref} as accessing the @var{k}th cdr of the list,
or returning the results of cdring @var{k} times down @var{lst}.
@end deffn

@c docstring begin (texi-doc-string "guile" "list-cdr-set!")
@deffn primitive list-cdr-set! list k val
Set the @var{k}th cdr of @var{list} to @var{val}.
@end deffn

@c docstring begin (texi-doc-string "guile" "list-head")
@deffn primitive list-head lst k
Copy the first @var{k} elements from @var{lst} into a new list, and
return it.
@end deffn

@c docstring begin (texi-doc-string "guile" "list-copy")
@deffn primitive list-copy lst
Return a (newly-created) copy of @var{lst}.
@end deffn

@c docstring begin (texi-doc-string "guile" "memq")
@deffn primitive memq x lst
Return the first sublist of LST whose car is `eq?' to X
where the sublists of LST are the non-empty lists returned
by `(list-tail LST K)' for K less than the length of LST.  If
X does not occur in LST, then `#f' (not the empty list) is
returned.
@end deffn

@c docstring begin (texi-doc-string "guile" "memv")
@deffn primitive memv x lst
Return the first sublist of LST whose car is `eqv?' to X
where the sublists of LST are the non-empty lists returned
by `(list-tail LST K)' for K less than the length of LST.  If
X does not occur in LST, then `#f' (not the empty list) is
returned.
@end deffn

@c docstring begin (texi-doc-string "guile" "member")
@deffn primitive member x lst
Return the first sublist of LST whose car is `equal?' to X
where the sublists of LST are the non-empty lists returned
by `(list-tail LST K)' for K less than the length of LST.  If
X does not occur in LST, then `#f' (not the empty list) is
returned.
@end deffn

@c docstring begin (texi-doc-string "guile" "delq")
@deffn primitive delq item lst
Return a newly-created copy of @var{lst} with elements `eq?' to @var{item} removed.
This procedure mirrors @code{memq}:
@code{delq} compares elements of @var{lst} against @var{item} with
@code{eq?}.
@end deffn

@c docstring begin (texi-doc-string "guile" "delv")
@deffn primitive delv item lst
Return a newly-created copy of @var{lst} with elements `eqv?' to @var{item} removed.
This procedure mirrors @code{memv}:
@code{delv} compares elements of @var{lst} against @var{item} with
@code{eqv?}.
@end deffn

@c docstring begin (texi-doc-string "guile" "delete")
@deffn primitive delete item lst
Return a newly-created copy of @var{lst} with elements `equal?' to @var{item} removed.
This procedure mirrors @code{member}:
@code{delete} compares elements of @var{lst} against @var{item} with
@code{equal?}.
@end deffn

@c docstring begin (texi-doc-string "guile" "delq!")
@c docstring begin (texi-doc-string "guile" "delv!")
@c docstring begin (texi-doc-string "guile" "delete!")
@deffn primitive delq! item lst
@deffnx primitive delv! item lst
@deffnx primitive delete! item lst
These procedures are destructive versions of @code{delq}, @code{delv}
and @code{delete}: they modify the pointers in the existing @var{lst}
rather than creating a new list.  Caveat evaluator: Like other
destructive list functions, these functions cannot modify the binding of
@var{lst}, and so cannot be used to delete the first element of
@var{lst} destructively.
@end deffn

@c docstring begin (texi-doc-string "guile" "delq1!")
@deffn primitive delq1! item lst
Like `delq!', but only deletes the first occurrence of ITEM from LST.
Tests for equality using `eq?'.  See also `delv1!' and `delete1!'.
@end deffn

@c docstring begin (texi-doc-string "guile" "delv1!")
@deffn primitive delv1! item lst
Like `delv!', but only deletes the first occurrence of ITEM from LST.
Tests for equality using `eqv?'.  See also `delq1!' and `delete1!'.
@end deffn

@c docstring begin (texi-doc-string "guile" "delete1!")
@deffn primitive delete1! item lst
Like `delete!', but only deletes the first occurrence of ITEM from LST.
Tests for equality using `equal?'.  See also `delq1!' and `delv1!'.
@end deffn

[FIXME: is there any reason to have the `sloppy' functions available at
high level at all?  Maybe these docs should be relegated to a "Guile
Internals" node or something. -twp]

@c docstring begin (texi-doc-string "guile" "sloppy-memq")
@deffn primitive sloppy-memq x lst
This procedure behaves like @code{memq}, but does no type or error checking.
Its use is recommended only in writing Guile internals,
not for high-level Scheme programs.
@end deffn

@c docstring begin (texi-doc-string "guile" "sloppy-memv")
@deffn primitive sloppy-memv x lst
This procedure behaves like @code{memv}, but does no type or error checking.
Its use is recommended only in writing Guile internals,
not for high-level Scheme programs.
@end deffn

@c docstring begin (texi-doc-string "guile" "sloppy-member")
@deffn primitive sloppy-member x lst
This procedure behaves like @code{member}, but does no type or error checking.
Its use is recommended only in writing Guile internals,
not for high-level Scheme programs.
@end deffn

@c begin (texi-doc-string "guile" "map")
@c docstring begin (texi-doc-string "guile" "map-in-order")
@deffn primitive map proc arg1 . args
@deffnx primitive map-in-order proc arg1 . args
@end deffn

@c begin (texi-doc-string "guile" "for-each")
@deffn primitive for-each proc arg1 . args
@end deffn


@node Records
@section Records

[FIXME: this is pasted in from Tom Lord's original guile.texi and should
be reviewed]

A @dfn{record type} is a first class object representing a user-defined
data type.  A @dfn{record} is an instance of a record type.

@deffn procedure record? obj
Returns @code{#t} if @var{obj} is a record of any type and @code{#f}
otherwise.

Note that @code{record?} may be true of any Scheme value; there is no
promise that records are disjoint with other Scheme types.
@end deffn

@deffn procedure make-record-type type-name field-names
Returns a @dfn{record-type descriptor}, a value representing a new data
type disjoint from all others.  The @var{type-name} argument must be a
string, but is only used for debugging purposes (such as the printed
representation of a record of the new type).  The @var{field-names}
argument is a list of symbols naming the @dfn{fields} of a record of the
new type.  It is an error if the list contains any duplicates.  It is
unspecified how record-type descriptors are represented.@refill
@end deffn

@deffn procedure record-constructor rtd [field-names]
Returns a procedure for constructing new members of the type represented
by @var{rtd}.  The returned procedure accepts exactly as many arguments
as there are symbols in the given list, @var{field-names}; these are
used, in order, as the initial values of those fields in a new record,
which is returned by the constructor procedure.  The values of any
fields not named in that list are unspecified.  The @var{field-names}
argument defaults to the list of field names in the call to
@code{make-record-type} that created the type represented by @var{rtd};
if the @var{field-names} argument is provided, it is an error if it
contains any duplicates or any symbols not in the default list.@refill
@end deffn

@deffn procedure record-predicate rtd
Returns a procedure for testing membership in the type represented by
@var{rtd}.  The returned procedure accepts exactly one argument and
returns a true value if the argument is a member of the indicated record
type; it returns a false value otherwise.@refill
@end deffn

@deffn procedure record-accessor rtd field-name
Returns a procedure for reading the value of a particular field of a
member of the type represented by @var{rtd}.  The returned procedure
accepts exactly one argument which must be a record of the appropriate
type; it returns the current value of the field named by the symbol
@var{field-name} in that record.  The symbol @var{field-name} must be a
member of the list of field-names in the call to @code{make-record-type}
that created the type represented by @var{rtd}.@refill
@end deffn

@deffn procedure record-modifier rtd field-name
Returns a procedure for writing the value of a particular field of a
member of the type represented by @var{rtd}.  The returned procedure
accepts exactly two arguments: first, a record of the appropriate type,
and second, an arbitrary Scheme value; it modifies the field named by
the symbol @var{field-name} in that record to contain the given value.
The returned value of the modifier procedure is unspecified.  The symbol
@var{field-name} must be a member of the list of field-names in the call
to @code{make-record-type} that created the type represented by
@var{rtd}.@refill
@end deffn

@deffn procedure record-type-descriptor record
Returns a record-type descriptor representing the type of the given
record.  That is, for example, if the returned descriptor were passed to
@code{record-predicate}, the resulting predicate would return a true
value when passed the given record.  Note that it is not necessarily the
case that the returned descriptor is the one that was passed to
@code{record-constructor} in the call that created the constructor
procedure that created the given record.@refill
@end deffn

@deffn procedure record-type-name rtd
Returns the type-name associated with the type represented by rtd.  The
returned value is @code{eqv?} to the @var{type-name} argument given in
the call to @code{make-record-type} that created the type represented by
@var{rtd}.@refill
@end deffn

@deffn procedure record-type-fields rtd
Returns a list of the symbols naming the fields in members of the type
represented by @var{rtd}.  The returned value is @code{equal?} to the
field-names argument given in the call to @code{make-record-type} that
created the type represented by @var{rtd}.@refill
@end deffn


@node Structures
@section Structures

[FIXME: this is pasted in from Tom Lord's original guile.texi and should
be reviewed]

A @dfn{structure type} is a first class user-defined data type.  A
@dfn{structure} is an instance of a structure type.  A structure type is
itself a structure.

Structures are less abstract and more general than traditional records.
In fact, in Guile Scheme, records are implemented using structures.

@menu
* Structure Concepts::          The structure of Structures
* Structure Layout::            Defining the layout of structure types
* Structure Basics::            make-, -ref and -set! procedures for structs
* Vtables::                     Accessing type-specific data
@end menu

@node  Structure Concepts
@subsection Structure Concepts

A structure object consists of a handle, structure data, and a vtable.
The handle is a Scheme value which points to both the vtable and the
structure's data.  Structure data is a dynamically allocated region of
memory, private to the structure, divided up into typed fields.  A
vtable is another structure used to hold type-specific data.  Multiple
structures can share a common vtable.

Three concepts are key to understanding structures.

@itemize @bullet{}
@item @dfn{layout specifications}

Layout specifications determine how memory allocated to structures is
divided up into fields.  Programmers must write a layout specification
whenever a new type of structure is defined.

@item @dfn{structural accessors}

Structure access is by field number.   There is only one set of
accessors common to all structure objects.

@item @dfn{vtables}

Vtables, themselves structures, are first class representations of
disjoint sub-types of structures in general.   In most cases, when a
new structure is created, programmers must specifiy a vtable for the
new structure.   Each vtable has a field describing the layout of its
instances.   Vtables can have additional, user-defined fields as well.
@end itemize



@node  Structure Layout
@subsection Structure Layout

When a structure is created, a region of memory is allocated to hold its
state.  The @dfn{layout} of the structure's type determines how that
memory is divided into fields.

Each field has a specified type.  There are only three types allowed, each
corresponding to a one letter code.  The allowed types are:

@itemize @bullet{}
@item 'u' -- unprotected

The field holds binary data that is not GC protected.

@item 'p' -- protected

The field holds a Scheme value and is GC protected.

@item 's' -- self

The field holds a Scheme value and is GC protected.  When a structure is
created with this type of field, the field is initialized to refer to
the structure's own handle.  This kind of field is mainly useful when
mixing Scheme and C code in which the C code may need to compute a
structure's handle given only the address of its malloced data.
@end itemize


Each field also has an associated access protection.   There are only
three kinds of protection, each corresponding to a one letter code.
The allowed protections are:

@itemize @bullet{}
@item 'w' -- writable

The field can be read and written.

@item 'r' -- readable

The field can be read, but not written.

@item 'o' -- opaque

The field can be neither read nor written.   This kind
of protection is for fields useful only to built-in routines.
@end itemize

A layout specification is described by stringing together pairs
of letters: one to specify a field type and one to specify a field
protection.    For example, a traditional cons pair type object could
be described as:

@example
; cons pairs have two writable fields of Scheme data
"pwpw"
@end example

A pair object in which the first field is held constant could be:

@example
"prpw"
@end example

Binary fields, (fields of type "u"), hold one @emph{word} each.  The
size of a word is a machine dependent value defined to be equal to the
value of the C expression: @code{sizeof (long)}.

The last field of a structure layout may specify a tail array.
A tail array is indicated by capitalizing the field's protection
code ('W', 'R' or 'O').   A tail-array field is replaced by
a read-only binary data field containing an array size.   The array
size is determined at the time the structure is created.  It is followed
by a corresponding number of fields of the type specified for the
tail array.   For example, a conventional Scheme vector can be
described as:

@example
; A vector is an arbitrary number of writable fields holding Scheme
; values:
"pW"
@end example

In the above example, field 0 contains the size of the vector and
fields beginning at 1 contain the vector elements.

A kind of tagged vector (a constant tag followed by conventioal
vector elements) might be:

@example
"prpW"
@end example


Structure layouts are represented by specially interned symbols whose
name is a string of type and protection codes.  To create a new
structure layout, use this procedure:

@c docstring begin (texi-doc-string "guile" "make-struct-layout")
@deffn primitive make-struct-layout fields
Return a new structure layout object.

@var{fields} must be a string made up of pairs of characters
strung together.  The first character of each pair describes a field
type, the second a field protection.  Allowed types are 'p' for
GC-protected Scheme data, 'u' for unprotected binary data, and 's' for
a field that points to the structure itself.    Allowed protections
are 'w' for mutable fields, 'r' for read-only fields, and 'o' for opaque
fields.  The last field protection specification may be capitalized to
indicate that the field is a tail-array.
@end deffn



@node Structure Basics
@subsection Structure Basics

This section describes the basic procedures for creating and accessing
structures.

@c docstring begin (texi-doc-string "guile" "make-struct")
@deffn primitive make-struct vtable tail_array_size . init
Create a new structure.

@var{type} must be a vtable structure (@pxref{Vtables}).

@var{tail-elts} must be a non-negative integer.  If the layout
specification indicated by @var{type} includes a tail-array,
this is the number of elements allocated to that array.

The @var{init1}, @dots{} are optional arguments describing how
successive fields of the structure should be initialized.  Only fields
with protection 'r' or 'w' can be initialized, except for fields of
type 's', which are automatically initialized to point to the new
structure itself; fields with protection 'o' can not be initialized by
Scheme programs.

If fewer optional arguments than initializable fields are supplied,
fields of type 'p' get default value #f while fields of type 'u' are
initialized to 0.

Structs are currently the basic representation for record-like data
structures in Guile.  The plan is to eventually replace them with a
new representation which will at the same time be easier to use and
more powerful.

For more information, see the documentation for @code{make-vtable-vtable}.
@end deffn

@c docstring begin (texi-doc-string "guile" "struct?")
@deffn primitive struct? x
Return #t iff @var{obj} is a structure object, else #f.
@end deffn


@c docstring begin (texi-doc-string "guile" "struct-ref")
@c docstring begin (texi-doc-string "guile" "struct-set!")
@deffn primitive struct-ref handle pos
@deffnx primitive struct-set! struct n value
Access (or modify) the @var{n}th field of @var{struct}.

If the field is of type 'p', then it can be set to an arbitrary value.

If the field is of type 'u', then it can only be set to a non-negative
integer value small enough to fit in one machine word.
@end deffn



@node  Vtables
@subsection Vtables

Vtables are structures that are used to represent structure types.  Each
vtable contains a layout specification in field
@code{vtable-index-layout} -- instances of the type are laid out
according to that specification.  Vtables contain additional fields
which are used only internally to libguile.  The variable
@code{vtable-offset-user} is bound to a field number.  Vtable fields
at that position or greater are user definable.

@c docstring begin (texi-doc-string "guile" "struct-vtable")
@deffn primitive struct-vtable handle
Return the vtable structure that describes the type of @var{struct}.
@end deffn

@c docstring begin (texi-doc-string "guile" "struct-vtable?")
@deffn primitive struct-vtable? x
Return #t iff obj is a vtable structure.
@end deffn

If you have a vtable structure, @code{V}, you can create an instance of
the type it describes by using @code{(make-struct V ...)}.  But where
does @code{V} itself come from?  One possibility is that @code{V} is an
instance of a user-defined vtable type, @code{V'}, so that @code{V} is
created by using @code{(make-struct V' ...)}.  Another possibility is
that @code{V} is an instance of the type it itself describes.  Vtable
structures of the second sort are created by this procedure:

@c docstring begin (texi-doc-string "guile" "make-vtable-vtable")
@deffn primitive make-vtable-vtable user_fields tail_array_size . init
Return a new, self-describing vtable structure.

@var{user-fields} is a string describing user defined fields of the
vtable beginning at index @code{vtable-offset-user}
(see @code{make-struct-layout}).

@var{tail-size} specifies the size of the tail-array (if any) of
this vtable.

@var{init1}, @dots{} are the optional initializers for the fields of
the vtable.

Vtables have one initializable system field---the struct printer.
This field comes before the user fields in the initializers passed
to @code{make-vtable-vtable} and @code{make-struct}, and thus works as
a third optional argument to @code{make-vtable-vtable} and a fourth to
@code{make-struct} when creating vtables:

If the value is a procedure, it will be called instead of the standard
printer whenever a struct described by this vtable is printed.
The procedure will be called with arguments STRUCT and PORT.

The structure of a struct is described by a vtable, so the vtable is
in essence the type of the struct.  The vtable is itself a struct with
a vtable.  This could go on forever if it weren't for the
vtable-vtables which are self-describing vtables, and thus terminate
the chain.

There are several potential ways of using structs, but the standard
one is to use three kinds of structs, together building up a type
sub-system: one vtable-vtable working as the root and one or several
"types", each with a set of "instances".  (The vtable-vtable should be
compared to the class <class> which is the class of itself.)

@example
(define ball-root (make-vtable-vtable "pr" 0))

(define (make-ball-type ball-color)
  (make-struct ball-root 0
	       (make-struct-layout "pw")
               (lambda (ball port)
                 (format port "#<a ~A ball owned by ~A>"
                         (color ball)
                         (owner ball)))
               ball-color))
(define (color ball) (struct-ref (struct-vtable ball) vtable-offset-user))
(define (owner ball) (struct-ref ball 0))

(define red (make-ball-type 'red))
(define green (make-ball-type 'green))

(define (make-ball type owner) (make-struct type 0 owner))

(define ball (make-ball green 'Nisse))
ball @result{} #<a green ball owned by Nisse>
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "struct-vtable-name")
@deffn primitive struct-vtable-name vtable
Return the name of the vtable @var{vtable}.
@end deffn

@c docstring begin (texi-doc-string "guile" "set-struct-vtable-name!")
@deffn primitive set-struct-vtable-name! vtable name
Set the name of the vtable @var{vtable} to @var{name}.
@end deffn

@c docstring begin (texi-doc-string "guile" "struct-vtable-tag")
@deffn primitive struct-vtable-tag handle
Return the vtable tag of the structure @var{handle}.
@end deffn


@node Arrays
@section Arrays

@menu
* Conventional Arrays::   Arrays with arbitrary data.
* Array Mapping::         Applying a procedure to the contents of an array.
* Uniform Arrays::        Arrays with data of a single type.
* Bit Vectors::           Vectors of bits.
@end menu

@node Conventional Arrays
@subsection Conventional Arrays

@dfn{Conventional arrays} are a collection of cells organised into an
arbitrary number of dimensions.  Each cell can hold any kind of Scheme
value and can be accessed in constant time by supplying an index for
each dimension.  This contrasts with uniform arrays, which use memory
more efficiently but can hold data of only a single type, and lists
where inserting and deleting cells is more efficient, but more time
is usually required to access a particular cell.

A conventional array is displayed as @code{#} followed by the @dfn{rank}
(number of dimensions) followed by the cells, organised into dimensions
using parentheses.  The nesting depth of the parentheses is equal to
the rank.

When an array is created, the number of dimensions and range of each
dimension must be specified, e.g., to create a 2x3 array with a
zero-based index:

@example
(make-array 'ho 2 3) @result{}
#2((ho ho ho) (ho ho ho))
@end example

The range of each dimension can also be given explicitly, e.g., another
way to create the same array:

@example
(make-array 'ho '(0 1) '(0 2)) @result{}
#2((ho ho ho) (ho ho ho))
@end example

A conventional array with one dimension based at zero is identical to
a vector:

@example
(make-array 'ho 3) @result{}
#(ho ho ho)
@end example

The following procedures can be used with conventional arrays (or vectors).

@c docstring begin (texi-doc-string "guile" "array?")
@deffn primitive array? v [prot]
Returns @code{#t} if the @var{obj} is an array, and @code{#f} if not.

The @var{prototype} argument is used with uniform arrays and is described
elsewhere.
@end deffn

@deffn procedure make-array initial-value bound1 bound2 @dots{}
Creates and returns an array that has as many dimensions as there are
@var{bound}s and fills it with @var{initial-value}.
@end deffn

@c array-ref's type is `compiled-closure'.  There's some weird stuff
@c going on in array.c, too.  Let's call it a primitive. -twp

@c docstring begin (texi-doc-string "guile" "uniform-vector-ref")
@c docstring begin (texi-doc-string "guile" "array-ref")
@deffn primitive uniform-vector-ref v args
@deffnx primitive array-ref v . args
Returns the element at the @code{(index1, index2)} element in @var{array}.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-in-bounds?")
@deffn primitive array-in-bounds? v . args
Returns @code{#t} if its arguments would be acceptable to array-ref.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-set!")
@c docstring begin (texi-doc-string "guile" "uniform-array-set1!")
@deffn primitive array-set! v obj . args
@deffnx primitive uniform-array-set1! v obj args
Sets the element at the @code{(index1, index2)} element in @var{array} to
@var{new-value}.  The value returned by array-set! is unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "make-shared-array")
@deffn primitive make-shared-array oldra mapfunc . dims
@code{make-shared-array} can be used to create shared subarrays of other
arrays.  The @var{mapper} is a function that translates coordinates in
the new array into coordinates in the old array.  A @var{mapper} must be
linear, and its range must stay within the bounds of the old array, but
it can be otherwise arbitrary.  A simple example:
@example
(define fred (make-array #f 8 8))
(define freds-diagonal
  (make-shared-array fred (lambda (i) (list i i)) 8))
(array-set! freds-diagonal 'foo 3)
(array-ref fred 3 3) @result{} foo
(define freds-center
  (make-shared-array fred (lambda (i j) (list (+ 3 i) (+ 3 j))) 2 2))
(array-ref freds-center 0 0) @result{} foo
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "shared-array-increments")
@deffn primitive shared-array-increments ra
For each dimension, return the distance between elements in the root vector.
@end deffn

@c docstring begin (texi-doc-string "guile" "shared-array-offset")
@deffn primitive shared-array-offset ra
Return the root vector index of the first element in the array.
@end deffn

@c docstring begin (texi-doc-string "guile" "shared-array-root")
@deffn primitive shared-array-root ra
Return the root vector of a shared array.
@end deffn

@c docstring begin (texi-doc-string "guile" "transpose-array")
@deffn primitive transpose-array ra . args
Returns an array sharing contents with @var{array}, but with dimensions
arranged in a different order.  There must be one @var{dim} argument for
each dimension of @var{array}.  @var{dim0}, @var{dim1}, @dots{} should
be integers between 0 and the rank of the array to be returned.  Each
integer in that range must appear at least once in the argument list.

The values of @var{dim0}, @var{dim1}, @dots{} correspond to dimensions
in the array to be returned, their positions in the argument list to
dimensions of @var{array}.  Several @var{dim}s may have the same value,
in which case the returned array will have smaller rank than
@var{array}.

examples:
@example
(transpose-array '#2((a b) (c d)) 1 0) @result{} #2((a c) (b d))
(transpose-array '#2((a b) (c d)) 0 0) @result{} #1(a d)
(transpose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 1 0) @result{}
                #2((a 4) (b 5) (c 6))
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "enclose-array")
@deffn primitive enclose-array ra . axes
@var{dim0}, @var{dim1} @dots{} should be nonnegative integers less than
the rank of @var{array}.  @var{enclose-array} returns an array
resembling an array of shared arrays.  The dimensions of each shared
array are the same as the @var{dim}th dimensions of the original array,
the dimensions of the outer array are the same as those of the original
array that did not match a @var{dim}.

An enclosed array is not a general Scheme array.  Its elements may not
be set using @code{array-set!}.  Two references to the same element of
an enclosed array will be @code{equal?} but will not in general be
@code{eq?}.  The value returned by @var{array-prototype} when given an
enclosed array is unspecified.

examples:
@example
(enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1) @result{}
   #<enclosed-array (#1(a d) #1(b e) #1(c f)) (#1(1 4) #1(2 5) #1(3 6))>

(enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 0) @result{}
   #<enclosed-array #2((a 1) (d 4)) #2((b 2) (e 5)) #2((c 3) (f 6))>
@end example
@end deffn

@deffn procedure array-shape array
Returns a list of inclusive bounds of integers.
@example
(array-shape (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) (0 4))
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "array-dimensions")
@deffn primitive array-dimensions ra
@code{Array-dimensions} is similar to @code{array-shape} but replaces
elements with a @code{0} minimum with one greater than the maximum. So:
@example
(array-dimensions (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) 5)
@end example
@end deffn

@c docstring begin (texi-doc-string "guile" "array-rank")
@deffn primitive array-rank ra
Returns the number of dimensions of @var{obj}.  If @var{obj} is not an
array, @code{0} is returned.
@end deffn

@c docstring begin (texi-doc-string "guile" "array->list")
@deffn primitive array->list v
Returns a list consisting of all the elements, in order, of @var{array}.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-copy!")
@c docstring begin (texi-doc-string "guile" "array-copy-in-order!")
@deffn primitive array-copy! src dst
@deffnx primitive array-copy-in-order! src dst
Copies every element from vector or array @var{source} to the
corresponding element of @var{destination}.  @var{destination} must have
the same rank as @var{source}, and be at least as large in each
dimension.  The order is unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-fill!")
@deffn primitive array-fill! ra fill
Stores @var{fill} in every element of @var{array}.  The value returned
is unspecified.
@end deffn

@c begin (texi-doc-string "guile" "array-equal?")
@deffn primitive array-equal? ra0 ra1
Returns @code{#t} iff all arguments are arrays with the same shape, the
same type, and have corresponding elements which are either
@code{equal?}  or @code{array-equal?}.  This function differs from
@code{equal?} in that a one dimensional shared array may be
@var{array-equal?} but not @var{equal?} to a vector or uniform vector.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-contents")
@deffn primitive array-contents ra [strict]
@deffnx primitive array-contents array strict
If @var{array} may be @dfn{unrolled} into a one dimensional shared array
without changing their order (last subscript changing fastest), then
@code{array-contents} returns that shared array, otherwise it returns
@code{#f}.  All arrays made by @var{make-array} and
@var{make-uniform-array} may be unrolled, some arrays made by
@var{make-shared-array} may not be.

If the optional argument @var{strict} is provided, a shared array will
be returned only if its elements are stored internally contiguous in
memory.
@end deffn

@node Array Mapping
@subsection Array Mapping

@c docstring begin (texi-doc-string "guile" "array-map!")
@c docstring begin (texi-doc-string "guile" "array-map-in-order!")
@deffn primitive array-map! ra0 proc . lra
@deffnx primitive array-map-in-order! ra0 proc . lra
@var{array1}, @dots{} must have the same number of dimensions as
@var{array0} and have a range for each index which includes the range
for the corresponding index in @var{array0}.  @var{proc} is applied to
each tuple of elements of @var{array1} @dots{} and the result is stored
as the corresponding element in @var{array0}.  The value returned is
unspecified.  The order of application is unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-for-each")
@deffn primitive array-for-each proc ra0 . lra
@var{proc} is applied to each tuple of elements of @var{array0} @dots{}
in row-major order.  The value returned is unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-index-map!")
@deffn primitive array-index-map! ra proc
applies @var{proc} to the indices of each element of @var{array} in
turn, storing the result in the corresponding element.  The value
returned and the order of application are unspecified.

One can implement @var{array-indexes} as
@example
(define (array-indexes array)
    (let ((ra (apply make-array #f (array-shape array))))
      (array-index-map! ra (lambda x x))
      ra))
@end example
Another example:
@example
(define (apl:index-generator n)
    (let ((v (make-uniform-vector n 1)))
      (array-index-map! v (lambda (i) i))
      v))
@end example
@end deffn

@node Uniform Arrays
@subsection Uniform Arrays

@noindent
@dfn{Uniform arrays} have elements all of the
same type and occupy less storage than conventional
arrays.  Uniform arrays with a single zero-based dimension
are also known as @dfn{uniform vectors}.  The procedures in
this section can also be used on conventional arrays, vectors,
bit-vectors and strings.

@noindent
When creating a uniform array, the type of data to be stored
is indicated with a @var{prototype} argument.  The following table
lists the types available and example prototypes:

@example
prototype           type                       printing character

#t             boolean (bit-vector)                    b
#\a            char (string)                           a
#\nul          byte (integer)                          y
's             short (integer)                         h
1              unsigned long (integer)                 u
-1             signed long (integer)                   e
'l             signed long long (integer)              l
1.0            float (single precision)                s
1/3            double (double precision float)         i
0+i            complex (double precision)              c
()             conventional vector
@end example

@noindent
Unshared uniform arrays of characters with a single zero-based dimension
are identical to strings:

@example
(make-uniform-array #\a 3) @result{}
"aaa"
@end example

@noindent
Unshared uniform arrays of booleans with a single zero-based dimension
are identical to @ref{Bit Vectors, bit-vectors}.

@example
(make-uniform-array #t 3) @result{}
#*111
@end example

@noindent
Other uniform vectors are written in a form similar to that of vectors,
except that a single character from the above table is put between
@code{#} and @code{(}.  For example, a uniform vector of signed
long integers is displayed in the form @code{'#e(3 5 9)}.

@c docstring begin (texi-doc-string "guile" "array?")
@deffn primitive array? v [prot]
Returns @code{#t} if the @var{obj} is an array, and @code{#f} if not.

The @var{prototype} argument is used with uniform arrays and is described
elsewhere.
@end deffn

@deffn procedure make-uniform-array prototype bound1 bound2 @dots{}
Creates and returns a uniform array of type corresponding to
@var{prototype} that has as many dimensions as there are @var{bound}s
and fills it with @var{prototype}.
@end deffn

@c docstring begin (texi-doc-string "guile" "array-prototype")
@deffn primitive array-prototype ra
Returns an object that would produce an array of the same type as
@var{array}, if used as the @var{prototype} for
@code{make-uniform-array}.
@end deffn

@c docstring begin (texi-doc-string "guile" "list->uniform-array")
@deffn primitive list->uniform-array ndim prot lst
@deffnx procedure list->uniform-vector prot lst
Returns a uniform array of the type indicated by prototype @var{prot}
with elements the same as those of @var{lst}.  Elements must be of the
appropriate type, no coercions are done.
@end deffn

@deffn primitive uniform-vector-fill! uve fill
Stores @var{fill} in every element of @var{uve}.  The value returned is
unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "uniform-vector-length")
@deffn primitive uniform-vector-length v
Returns the number of elements in @var{uve}.
@end deffn

@c docstring begin (texi-doc-string "guile" "dimensions->uniform-array")
@deffn primitive dimensions->uniform-array dims prot [fill]
@deffnx primitive make-uniform-vector length prototype [fill]
Creates and returns a uniform array or vector of type corresponding to
@var{prototype} with dimensions @var{dims} or length @var{length}.  If
@var{fill} is supplied, it's used to fill the array, otherwise
@var{prototype} is used.
@end deffn

@c Another compiled-closure. -twp

@c docstring begin (texi-doc-string "guile" "uniform-array-read!")
@deffn primitive uniform-array-read! ra [port_or_fd [start [end]]]
@deffnx primitive uniform-vector-read! uve [port-or-fdes] [start] [end]
Attempts to read all elements of @var{ura}, in lexicographic order, as
binary objects from @var{port-or-fdes}.
If an end of file is encountered during
uniform-array-read! the objects up to that point only are put into @var{ura}
(starting at the beginning) and the remainder of the array is
unchanged.

The optional arguments @var{start} and @var{end} allow
a specified region of a vector (or linearized array) to be read,
leaving the remainder of the vector unchanged.

@code{uniform-array-read!} returns the number of objects read.
@var{port-or-fdes} may be omitted, in which case it defaults to the value
returned by @code{(current-input-port)}.
@end deffn

@c docstring begin (texi-doc-string "guile" "uniform-array-write")
@deffn primitive uniform-array-write v [port_or_fd [start [end]]]
@deffnx primitive uniform-vector-write uve [port-or-fdes] [start] [end]
Writes all elements of @var{ura} as binary objects to
@var{port-or-fdes}.

The optional arguments @var{start}
and @var{end} allow
a specified region of a vector (or linearized array) to be written.

The number of objects actually written is returned.
@var{port-or-fdes} may be
omitted, in which case it defaults to the value returned by
@code{(current-output-port)}.
@end deffn

@node Bit Vectors
@subsection Bit Vectors

@noindent
Bit vectors are a specific type of uniform array: an array of booleans
with a single zero-based index.

@noindent
They are displayed as a sequence of @code{0}s and
@code{1}s prefixed by @code{#*}, e.g.,

@example
(make-uniform-vector 8 #t #f) @result{}
#*00000000

#b(#t #f #t) @result{}
#*101
@end example

@c docstring begin (texi-doc-string "guile" "bit-count")
@deffn primitive bit-count b bitvector
Returns the number of occurrences of the boolean @var{b} in
@var{bitvector}.
@end deffn

@c docstring begin (texi-doc-string "guile" "bit-position")
@deffn primitive bit-position item v k
Returns the minimum index of an occurrence of @var{bool} in @var{bv}
which is at least @var{k}.  If no @var{bool} occurs within the specified
range @code{#f} is returned.
@end deffn

@c docstring begin (texi-doc-string "guile" "bit-invert!")
@deffn primitive bit-invert! v
Modifies @var{bv} by replacing each element with its negation.
@end deffn

@c docstring begin (texi-doc-string "guile" "bit-set*!")
@deffn primitive bit-set*! v kv obj
If uve is a bit-vector @var{bv} and uve must be of the same
length.  If @var{bool} is @code{#t}, uve is OR'ed into
@var{bv}; If @var{bool} is @code{#f}, the inversion of uve is
AND'ed into @var{bv}.

If uve is a unsigned integer vector all the elements of uve
must be between 0 and the @code{length} of @var{bv}.  The bits
of @var{bv} corresponding to the indexes in uve are set to
@var{bool}.  The return value is unspecified.
@end deffn

@c docstring begin (texi-doc-string "guile" "bit-count*")
@deffn primitive bit-count* v kv obj
Returns
@example
(bit-count (bit-set*! (if bool bv (bit-invert! bv)) uve #t) #t).
@end example
@var{bv} is not modified.
@end deffn


@node Association Lists and Hash Tables
@section Association Lists and Hash Tables

This chapter discusses dictionary objects: data structures that are
useful for organizing and indexing large bodies of information.

@menu
* Dictionary Types::            About dictionary types; what they're good for.
* Association Lists::
* Hash Tables::
@end menu

@node Dictionary Types
@subsection Dictionary Types

A @dfn{dictionary} object is a data structure used to index
information in a user-defined way.  In standard Scheme, the main
aggregate data types are lists and vectors.  Lists are not really
indexed at all, and vectors are indexed only by number
(e.g. @code{(vector-ref foo 5)}).  Often you will find it useful
to index your data on some other type; for example, in a library
catalog you might want to look up a book by the name of its
author.  Dictionaries are used to help you organize information in
such a way.

An @dfn{association list} (or @dfn{alist} for short) is a list of
key-value pairs.  Each pair represents a single quantity or
object; the @code{car} of the pair is a key which is used to
identify the object, and the @code{cdr} is the object's value.

A @dfn{hash table} also permits you to index objects with
arbitrary keys, but in a way that makes looking up any one object
extremely fast.  A well-designed hash system makes hash table
lookups almost as fast as conventional array or vector references.

Alists are popular among Lisp programmers because they use only
the language's primitive operations (lists, @dfn{car}, @dfn{cdr}
and the equality primitives).  No changes to the language core are
necessary.  Therefore, with Scheme's built-in list manipulation
facilities, it is very convenient to handle data stored in an
association list.  Also, alists are highly portable and can be
easily implemented on even the most minimal Lisp systems.

However, alists are inefficient, especially for storing large
quantities of data.  Because we want Guile to be useful for large
software systems as well as small ones, Guile provides a rich set
of tools for using either association lists or hash tables.

@node Association Lists
@subsection Association Lists
@cindex Association List
@cindex Alist
@cindex Database

An association list is a conventional data structure that is often used
to implement simple key-value databases.  It consists of a list of
entries in which each entry is a pair.  The @dfn{key} of each entry is
the @code{car} of the pair and the @dfn{value} of each entry is the
@code{cdr}.

@example
ASSOCIATION LIST ::=  '( (KEY1 . VALUE1)
                         (KEY2 . VALUE2)
                         (KEY3 . VALUE3)
                         @dots{}
                       )
@end example

@noindent
Association lists are also known, for short, as @dfn{alists}.

The structure of an association list is just one example of the infinite
number of possible structures that can be built using pairs and lists.
As such, the keys and values in an association list can be manipulated
using the general list structure procedures @code{cons}, @code{car},
@code{cdr}, @code{set-car!}, @code{set-cdr!} and so on.  However,
because association lists are so useful, Guile also provides specific
procedures for manipulating them.

@menu
* Alist Key Equality::
* Adding or Setting Alist Entries::
* Retrieving Alist Entries::
* Removing Alist Entries::
* Sloppy Alist Functions::
* Alist Example::
@end menu

@node Alist Key Equality
@subsubsection Alist Key Equality

All of Guile's dedicated association list procedures, apart from
@code{acons}, come in three flavours, depending on the level of equality
that is required to decide whether an existing key in the association
list is the same as the key that the procedure call uses to identify the
required entry.

@itemize @bullet
@item
Procedures with @dfn{assq} in their name use @code{eq?} to determine key
equality.

@item
Procedures with @dfn{assv} in their name use @code{eqv?} to determine
key equality.

@item
Procedures with @dfn{assoc} in their name use @code{equal?} to
determine key equality.
@end itemize

@code{acons} is an exception because it is used to build association
lists which do not require their entries' keys to be unique.

@node Adding or Setting Alist Entries
@subsubsection Adding or Setting Alist Entries
@findex acons
@findex assq-set!
@findex assv-set!
@findex assoc-set!
@r5index assq-set!
@r5index assv-set!
@r5index assoc-set!

@code{acons} adds a new entry to an association list and returns the
combined association list.  The combined alist is formed by consing the
new entry onto the head of the alist specified in the @code{acons}
procedure call.  So the specified alist is not modified, but its
contents become shared with the tail of the combined alist that
@code{acons} returns.

In the most common usage of @code{acons}, a variable holding the
original association list is updated with the combined alist:

@example
(set! address-list (acons name address address-list))
@end example

In such cases, it doesn't matter that the old and new values of
@code{address-list} share some of their contents, since the old value is
usually no longer independently accessible.

Note that @code{acons} adds the specified new entry regardless of
whether the alist may already contain entries with keys that are, in
some sense, the same as that of the new entry.  Thus @code{acons} is
ideal for building alists where there is no concept of key uniqueness.

@example
(set! task-list (acons 3 "pay gas bill" '()))
task-list
@result{}
((3 . "pay gas bill"))

(set! task-list (acons 3 "tidy bedroom" task-list))
task-list
@result{}
((3 . "tidy bedroom") (3 . "pay gas bill"))
@end example

@code{assq-set!}, @code{assv-set!} and @code{assoc-set!} are used to add
or replace an entry in an association list where there @emph{is} a
concept of key uniqueness.  If the specified association list already
contains an entry whose key is the same as that specified in the
procedure call, the existing entry is replaced by the new one.
Otherwise, the new entry is consed onto the head of the old association
list to create the combined alist.  In all cases, these procedures
return the combined alist.

@code{assq-set!} and friends @emph{may} destructively modify the
structure of the old association list in such a way that an existing
variable is correctly updated without having to @code{set!} it to the
value returned:

@example
address-list
@result{}
(("mary" . "34 Elm Road") ("james" . "16 Bow Street"))

(assoc-set! address-list "james" "1a London Road")
@result{}
(("mary" . "34 Elm Road") ("james" . "1a London Road"))

address-list
@result{}
(("mary" . "34 Elm Road") ("james" . "1a London Road"))
@end example

Or they may not:

@example
(assoc-set! address-list "bob" "11 Newington Avenue")
@result{}
(("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
 ("james" . "1a London Road"))

address-list
@result{}
(("mary" . "34 Elm Road") ("james" . "1a London Road"))
@end example

The only safe way to update an association list variable when adding or
replacing an entry like this is to @code{set!} the variable to the
returned value:

@example
(set! address-list
      (assoc-set! address-list "bob" "11 Newington Avenue"))
address-list
@result{}
(("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
 ("james" . "1a London Road"))
@end example

Because of this slight inconvenience, you may find it more convenient to
use hash tables to store dictionary data.  If your application will not
be modifying the contents of an alist very often, this may not make much
difference to you.

If you need to keep the old value of an association list in a form
independent from the list that results from modification by
@code{acons}, @code{assq-set!}, @code{assv-set!} or @code{assoc-set!},
use @code{list-copy} to copy the old association list before modifying
it.

@c docstring begin (texi-doc-string "guile" "acons")
@deffn primitive acons key value alist
Adds a new key-value pair to @var{alist}.  A new pair is
created whose car is @var{key} and whose cdr is @var{value}, and the
pair is consed onto @var{alist}, and the new list is returned.  This
function is @emph{not} destructive; @var{alist} is not modified.
@end deffn

@c docstring begin (texi-doc-string "guile" "assq-set!")
@c docstring begin (texi-doc-string "guile" "assv-set!")
@c docstring begin (texi-doc-string "guile" "assoc-set!")
@deffn primitive assq-set! alist key val
@deffnx primitive assv-set! alist key value
@deffnx primitive assoc-set! alist key value
Reassociate @var{key} in @var{alist} with @var{value}: find any existing
@var{alist} entry for @var{key} and associate it with the new
@var{value}.  If @var{alist} does not contain an entry for @var{key},
add a new one.  Return the (possibly new) alist.

These functions do not attempt to verify the structure of @var{alist},
and so may cause unusual results if passed an object that is not an
association list.
@end deffn

@node Retrieving Alist Entries
@subsubsection Retrieving Alist Entries
@findex assq
@findex assv
@findex assoc
@findex assq-ref
@findex assv-ref
@findex assoc-ref
@r5index assq
@r5index assv
@r5index assoc
@r5index assq-ref
@r5index assv-ref
@r5index assoc-ref

@code{assq}, @code{assv} and @code{assoc} take an alist and a key as
arguments and return the entry for that key if an entry exists, or
@code{#f} if there is no entry for that key.  Note that, in the cases
where an entry exists, these procedures return the complete entry, that
is @code{(KEY . VALUE)}, not just the value.

@c docstring begin (texi-doc-string "guile" "assq")
@c docstring begin (texi-doc-string "guile" "assv")
@c docstring begin (texi-doc-string "guile" "assoc")
@deffn primitive assq key alist
@deffnx primitive assv key alist
@deffnx primitive assoc key alist
Fetches the entry in @var{alist} that is associated with @var{key}.  To
decide whether the argument @var{key} matches a particular entry in
@var{alist}, @code{assq} compares keys with @code{eq?}, @code{assv}
uses @code{eqv?} and @code{assoc} uses @code{equal?}.  If @var{key}
cannot be found in @var{alist} (according to whichever equality
predicate is in use), then @code{#f} is returned.  These functions
return the entire alist entry found (i.e. both the key and the value).
@end deffn

@code{assq-ref}, @code{assv-ref} and @code{assoc-ref}, on the other
hand, take an alist and a key and return @emph{just the value} for that
key, if an entry exists.  If there is no entry for the specified key,
these procedures return @code{#f}.

This creates an ambiguity: if the return value is @code{#f}, it means
either that there is no entry with the specified key, or that there
@emph{is} an entry for the specified key, with value @code{#f}.
Consequently, @code{assq-ref} and friends should only be used where it
is known that an entry exists, or where the ambiguity doesn't matter
for some other reason.

@c docstring begin (texi-doc-string "guile" "assq-ref")
@c docstring begin (texi-doc-string "guile" "assv-ref")
@c docstring begin (texi-doc-string "guile" "assoc-ref")
@deffn primitive assq-ref alist key
@deffnx primitive assv-ref alist key
@deffnx primitive assoc-ref alist key
Like @code{assq}, @code{assv} and @code{assoc}, except that only the
value associated with @var{key} in @var{alist} is returned.  These
functions are equivalent to

@lisp
(let ((ent (@var{associator} @var{key} @var{alist})))
  (and ent (cdr ent)))
@end lisp

where @var{associator} is one of @code{assq}, @code{assv} or @code{assoc}.
@end deffn

@node Removing Alist Entries
@subsubsection Removing Alist Entries
@findex assq-remove!
@findex assv-remove!
@findex assoc-remove!

To remove the element from an association list whose key matches a
specified key, use @code{assq-remove!}, @code{assv-remove!} or
@code{assoc-remove!} (depending, as usual, on the level of equality
required between the key that you specify and the keys in the
association list).

As with @code{assq-set!} and friends, the specified alist may or may not
be modified destructively, and the only safe way to update a variable
containing the alist is to @code{set!} it to the value that
@code{assq-remove!} and friends return.

@example
address-list
@result{}
(("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
 ("james" . "1a London Road"))

(set! address-list (assoc-remove! address-list "mary"))
address-list
@result{}
(("bob" . "11 Newington Avenue") ("james" . "1a London Road"))
@end example

Note that, when @code{assq/v/oc-remove!} is used to modify an
association list that has been constructed only using the corresponding
@code{assq/v/oc-set!}, there can be at most one matching entry in the
alist, so the question of multiple entries being removed in one go does
not arise.  If @code{assq/v/oc-remove!} is applied to an association
list that has been constructed using @code{acons}, or an
@code{assq/v/oc-set!} with a different level of equality, or any mixture
of these, it removes only the first matching entry from the alist, even
if the alist might contain further matching entries.  For example:

@example
(define address-list '())
(set! address-list (assq-set! address-list "mary" "11 Elm Street"))
(set! address-list (assq-set! address-list "mary" "57 Pine Drive"))
address-list
@result{}
(("mary" . "57 Pine Drive") ("mary" . "11 Elm Street"))

(set! address-list (assoc-remove! address-list "mary"))
address-list
@result{}
(("mary" . "11 Elm Street"))
@end example

In this example, the two instances of the string "mary" are not the same
when compared using @code{eq?}, so the two @code{assq-set!} calls add
two distinct entries to @code{address-list}.  When compared using
@code{equal?}, both "mary"s in @code{address-list} are the same as the
"mary" in the @code{assoc-remove!} call, but @code{assoc-remove!} stops
after removing the first matching entry that it finds, and so one of the
"mary" entries is left in place.

@c docstring begin (texi-doc-string "guile" "assq-remove!")
@c docstring begin (texi-doc-string "guile" "assv-remove!")
@c docstring begin (texi-doc-string "guile" "assoc-remove!")
@deffn primitive assq-remove! alist key
@deffnx primitive assv-remove! alist key
@deffnx primitive assoc-remove! alist key
Delete the first entry in @var{alist} associated with @var{key}, and return
the resulting alist.
@end deffn

@node Sloppy Alist Functions
@subsubsection Sloppy Alist Functions
@findex sloppy-assq
@findex sloppy-assv
@findex sloppy-assoc

@code{sloppy-assq}, @code{sloppy-assv} and @code{sloppy-assoc} behave
like the corresponding non-@code{sloppy-} procedures, except that they
return @code{#f} when the specified association list is not well-formed,
where the non-@code{sloppy-} versions would signal an error.

Specifically, there are two conditions for which the non-@code{sloppy-}
procedures signal an error, which the @code{sloppy-} procedures handle
instead by returning @code{#f}.  Firstly, if the specified alist as a
whole is not a proper list:

@example
(assoc "mary" '((1 . 2) ("key" . "door") . "open sesame"))
@result{}
ERROR: In procedure assoc in expression (assoc "mary" (quote #)):
ERROR: Wrong type argument in position 2 (expecting NULLP): "open sesame"
ABORT: (wrong-type-arg)

(sloppy-assoc "mary" '((1 . 2) ("key" . "door") . "open sesame"))
@result{}
#f
@end example

@noindent
Secondly, if one of the entries in the specified alist is not a pair:

@example
(assoc 2 '((1 . 1) 2 (3 . 9)))
@result{}
ERROR: In procedure assoc in expression (assoc 2 (quote #)):
ERROR: Wrong type argument in position 2 (expecting CONSP): 2
ABORT: (wrong-type-arg)

(sloppy-assoc 2 '((1 . 1) 2 (3 . 9)))
@result{}
#f
@end example

Unless you are explicitly working with badly formed association lists,
it is much safer to use the non-@code{sloppy-} procedures, because they
help to highlight coding and data errors that the @code{sloppy-}
versions would silently cover up.

@c docstring begin (texi-doc-string "guile" "sloppy-assq")
@deffn primitive sloppy-assq key alist
Behaves like @code{assq} but does not do any error checking.
Recommended only for use in Guile internals.
@end deffn

@c docstring begin (texi-doc-string "guile" "sloppy-assv")
@deffn primitive sloppy-assv key alist
Behaves like @code{assv} but does not do any error checking.
Recommended only for use in Guile internals.
@end deffn

@c docstring begin (texi-doc-string "guile" "sloppy-assoc")
@deffn primitive sloppy-assoc key alist
Behaves like @code{assoc} but does not do any error checking.
Recommended only for use in Guile internals.
@end deffn

@node Alist Example
@subsubsection Alist Example

Here is a longer example of how alists may be used in practice.

@lisp
(define capitals '(("New York" . "Albany")
                   ("Oregon"   . "Salem")
                   ("Florida"  . "Miami")))

;; What's the capital of Oregon?
(assoc "Oregon" capitals)       @result{} ("Oregon" . "Salem")
(assoc-ref capitals "Oregon")   @result{} "Salem"

;; We left out South Dakota.
(set! capitals
      (assoc-set! capitals "South Dakota" "Bismarck"))
capitals
@result{} (("South Dakota" . "Bismarck")
    ("New York" . "Albany")
    ("Oregon" . "Salem")
    ("Florida" . "Miami"))

;; And we got Florida wrong.
(set! capitals
      (assoc-set! capitals "Florida" "Tallahassee"))
capitals
@result{} (("South Dakota" . "Bismarck")
    ("New York" . "Albany")
    ("Oregon" . "Salem")
    ("Florida" . "Tallahassee"))

;; After Oregon secedes, we can remove it.
(set! capitals
      (assoc-remove! capitals "Oregon"))
capitals
@result{} (("South Dakota" . "Bismarck")
    ("New York" . "Albany")
    ("Florida" . "Tallahassee"))
@end lisp

@node Hash Tables
@subsection Hash Tables

Like the association list functions, the hash table functions come
in several varieties: @code{hashq}, @code{hashv}, and @code{hash}.
The @code{hashq} functions use @code{eq?} to determine whether two
keys match.  The @code{hashv} functions use @code{eqv?}, and the
@code{hash} functions use @code{equal?}.

In each of the functions that follow, the @var{table} argument
must be a vector.  The @var{key} and @var{value} arguments may be
any Scheme object.

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hashq-ref")
@deffn primitive hashq-ref table obj [dflt]
Look up @var{key} in the hash table @var{table}, and return the
value (if any) associated with it.  If @var{key} is not found,
return @var{default} (or @code{#f} if no @var{default} argument is
supplied).  Uses `eq?' for equality testing.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hashv-ref")
@deffn primitive hashv-ref table obj [dflt]
Look up @var{key} in the hash table @var{table}, and return the
value (if any) associated with it.  If @var{key} is not found,
return @var{default} (or @code{#f} if no @var{default} argument is
supplied).  Uses `eqv?' for equality testing.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hash-ref")
@deffn primitive hash-ref table obj [dflt]
Look up @var{key} in the hash table @var{table}, and return the
value (if any) associated with it.  If @var{key} is not found,
return @var{default} (or @code{#f} if no @var{default} argument is
supplied).  Uses `equal?' for equality testing.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hashq-set!")
@deffn primitive hashq-set! table obj val
Find the entry in @var{table} associated with @var{key}, and store
@var{value} there. Uses `eq?' for equality testing.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hashv-set!")
@deffn primitive hashv-set! table obj val
Find the entry in @var{table} associated with @var{key}, and store
@var{value} there. Uses `eqv?' for equality testing.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hash-set!")
@deffn primitive hash-set! table obj val
Find the entry in @var{table} associated with @var{key}, and store
@var{value} there. Uses `equal?' for equality testing.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hashq-remove!")
@deffn primitive hashq-remove! table obj
Remove @var{key} (and any value associated with it) from @var{table}.
Uses `eq?' for equality tests.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hashv-remove!")
@deffn primitive hashv-remove! table obj
Remove @var{key} (and any value associated with it) from @var{table}.
Uses `eqv?' for equality tests.
@end deffn

@c ARGFIXME obj/key
@c docstring begin (texi-doc-string "guile" "hash-remove!")
@deffn primitive hash-remove! table obj
Remove @var{key} (and any value associated with it) from @var{table}.
Uses `equal?' for equality tests.
@end deffn

The standard hash table functions may be too limited for some
applications.  For example, you may want a hash table to store
strings in a case-insensitive manner, so that references to keys
named ``foobar'', ``FOOBAR'' and ``FooBaR'' will all yield the
same item.  Guile provides you with @dfn{extended} hash tables
that permit you to specify a hash function and associator function
of your choosing.  The functions described in the rest of this section
can be used to implement such custom hash table structures.

If you are unfamiliar with the inner workings of hash tables, then
this facility will probably be a little too abstract for you to
use comfortably.  If you are interested in learning more, see an
introductory textbook on data structures or algorithms for an
explanation of how hash tables are implemented.

@c docstring begin (texi-doc-string "guile" "hashq")
@deffn primitive hashq key size
Determine a hash value for KEY that is suitable for lookups in
a hashtable of size SIZE, where eq? is used as the equality
predicate.  The function returns an integer in the range 0 to
SIZE - 1.  NOTE that `hashq' may use internal addresses.
Thus two calls to hashq where the keys are eq? are not
guaranteed to deliver the same value if the key object gets
garbage collected in between.  This can happen, for example
with symbols:  (hashq 'foo n) (gc) (hashq 'foo n) may produce two
different values, since 'foo will be garbage collected.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashv")
@deffn primitive hashv key size
Determine a hash value for KEY that is suitable for lookups in
a hashtable of size SIZE, where eqv? is used as the equality
predicate.  The function returns an integer in the range 0 to
SIZE - 1.  NOTE that (hashv key) may use internal addresses.
Thus two calls to hashv where the keys are eqv? are not
guaranteed to deliver the same value if the key object gets
garbage collected in between.  This can happen, for example
with symbols:  (hashv 'foo n) (gc) (hashv 'foo n) may produce two
different values, since 'foo will be garbage collected.
@end deffn

@c docstring begin (texi-doc-string "guile" "hash")
@deffn primitive hash key size
Determine a hash value for KEY that is suitable for lookups in
a hashtable of size SIZE, where equal? is used as the equality
predicate.  The function returns an integer in the range 0 to
SIZE - 1.
@end deffn

@c ARGFIXME hash/hasher
@c docstring begin (texi-doc-string "guile" "hashx-ref")
@deffn primitive hashx-ref hash assoc table obj [dflt]
This behaves the same way as the corresponding @code{ref}
function, but uses @var{hasher} as a
hash function and @var{assoc} to compare keys.  @code{hasher} must
be a function that takes two arguments, a key to be hashed and a
table size.  @code{assoc} must be an associator function, like
@code{assoc}, @code{assq} or @code{assv}.

By way of illustration, @code{hashq-ref table key} is equivalent
to @code{hashx-ref hashq assq table key}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashx-set!")
@deffn primitive hashx-set! hash assoc table obj val
This behaves the same way as the corresponding @code{set!}
function, but uses @var{hasher} as a
hash function and @var{assoc} to compare keys.  @code{hasher} must
be a function that takes two arguments, a key to be hashed and a
table size.  @code{assoc} must be an associator function, like
@code{assoc}, @code{assq} or @code{assv}.

By way of illustration, @code{hashq-set! table key} is equivalent
to @code{hashx-set! hashq assq table key}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashq-get-handle")
@deffn primitive hashq-get-handle table obj
This procedure is similar to its @code{-ref} cousin, but returns a
@dfn{handle} from the hash table rather than the value associated with
@var{key}.  By convention, a handle in a hash table is the pair which
associates a key with a value.  Where @code{hashq-ref table key} returns
only a @code{value}, @code{hashq-get-handle table key} returns the pair
@code{(key . value)}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashv-get-handle")
@deffn primitive hashv-get-handle table obj
This procedure is similar to its @code{-ref} cousin, but returns a
@dfn{handle} from the hash table rather than the value associated with
@var{key}.  By convention, a handle in a hash table is the pair which
associates a key with a value.  Where @code{hashv-ref table key} returns
only a @code{value}, @code{hashv-get-handle table key} returns the pair
@code{(key . value)}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hash-get-handle")
@deffn primitive hash-get-handle table obj
This procedure is similar to its @code{-ref} cousin, but returns a
@dfn{handle} from the hash table rather than the value associated with
@var{key}.  By convention, a handle in a hash table is the pair which
associates a key with a value.  Where @code{hash-ref table key} returns
only a @code{value}, @code{hash-get-handle table key} returns the pair
@code{(key . value)}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashx-get-handle")
@deffn primitive hashx-get-handle hash assoc table obj
This behaves the same way as the corresponding @code{-get-handle}
function, but uses @var{hasher} as a
hash function and @var{assoc} to compare keys.  @code{hasher} must
be a function that takes two arguments, a key to be hashed and a
table size.  @code{assoc} must be an associator function, like
@code{assoc}, @code{assq} or @code{assv}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashq-create-handle!")
@deffn primitive hashq-create-handle! table key init
This function looks up @var{key} in @var{table} and returns its handle.
If @var{key} is not already present, a new handle is created which
associates @var{key} with @var{init}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashv-create-handle!")
@deffn primitive hashv-create-handle! table key init
This function looks up @var{key} in @var{table} and returns its handle.
If @var{key} is not already present, a new handle is created which
associates @var{key} with @var{init}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hash-create-handle!")
@deffn primitive hash-create-handle! table key init
This function looks up @var{key} in @var{table} and returns its handle.
If @var{key} is not already present, a new handle is created which
associates @var{key} with @var{init}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hashx-create-handle!")
@deffn primitive hashx-create-handle! hash assoc table obj init
This behaves the same way as the corresponding @code{-create-handle}
function, but uses @var{hasher} as a
hash function and @var{assoc} to compare keys.  @code{hasher} must
be a function that takes two arguments, a key to be hashed and a
table size.  @code{assoc} must be an associator function, like
@code{assoc}, @code{assq} or @code{assv}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hash-fold")
@deffn primitive hash-fold proc init table
An iterator over hash-table elements.
Accumulates and returns a result by applying PROC successively.
The arguments to PROC are "(key value prior-result)" where key
and value are successive pairs from the hash table TABLE, and
prior-result is either INIT (for the first application of PROC)
or the return value of the previous application of PROC.
For example, @code{(hash-fold acons () tab)} will convert a hash
table into an a-list of key-value pairs.
@end deffn


@node Vectors
@section Vectors

@c docstring begin (texi-doc-string "guile" "make-vector")
@deffn primitive make-vector k [fill]
Returns a newly allocated vector of @var{k} elements.  If a second
argument is given, then each element is initialized to @var{fill}.
Otherwise the initial contents of each element is unspecified. (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "vector")
@c docstring begin (texi-doc-string "guile" "list->vector")
@deffn primitive vector . l
@deffnx primitive list->vector l
Returns a newly allocated vector whose elements contain the given
arguments.  Analogous to @samp{list}. (r5rs)

@format
@t{(vector 'a 'b 'c)                      ==>  #(a b c) }
@end format
@end deffn

@c docstring begin (texi-doc-string "guile" "vector->list")
@deffn primitive vector->list v
@samp{Vector->list} returns a newly allocated list of the objects contained
in the elements of @var{vector}.  (r5rs)

@format
@t{(vector->list '#(dah dah didah))
=>  (dah dah didah)
list->vector '(dididit dah))
=>  #(dididit dah)
}
@end format
@end deffn

@c docstring begin (texi-doc-string "guile" "vector-fill!")
@deffn primitive vector-fill! v fill_x
Stores @var{fill} in every element of @var{vector}.
The value returned by @samp{vector-fill!} is unspecified. (r5rs)
@end deffn

@c docstring begin (texi-doc-string "guile" "vector?")
@deffn primitive vector? obj
Returns @t{#t} if @var{obj} is a vector, otherwise returns @t{#f}. (r5rs)
@end deffn


@node Hooks
@section Hooks

@c docstring begin (texi-doc-string "guile" "make-hook-with-name")
@deffn primitive make-hook-with-name name [n_args]
Create a named hook with the name @var{name} for storing
procedures of arity @var{n_args}.
@end deffn

@c docstring begin (texi-doc-string "guile" "make-hook")
@deffn primitive make-hook [n_args]
Create a hook for storing procedure of arity @var{n_args}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hook?")
@deffn primitive hook? x
Return @code{#t} if @var{x} is a hook.
@end deffn

@c docstring begin (texi-doc-string "guile" "hook-empty?")
@deffn primitive hook-empty? hook
Return @code{#t} if @var{hook} is an empty hook.
@end deffn

@c docstring begin (texi-doc-string "guile" "add-hook!")
@deffn primitive add-hook! hook proc [append_p]
Add the procedure @var{proc} to the hook @var{hook}. The
procedure is added to the end if @var{append_p} is true,
otherwise it is added to the front.
@end deffn

@c docstring begin (texi-doc-string "guile" "remove-hook!")
@deffn primitive remove-hook! hook proc
Remove the procedure @var{proc} from the hook @var{hook}.
@end deffn

@c docstring begin (texi-doc-string "guile" "reset-hook!")
@deffn primitive reset-hook! hook
Remove all procedures from the hook @var{hook}.
@end deffn

@c docstring begin (texi-doc-string "guile" "run-hook")
@deffn primitive run-hook hook . args
Apply all procedures from the hook @var{hook} to the arguments
@var{args}.
@end deffn

@c docstring begin (texi-doc-string "guile" "hook->list")
@deffn primitive hook->list hook
Convert the procedure list of @var{hook} to a list.
@end deffn


@node Other Data Types
@section Other Core Guile Data Types


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