693 lines
25 KiB
Racket
693 lines
25 KiB
Racket
#lang scribble/doc
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@require["mz.ss"]
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@title[#:style 'toc #:tag "data"]{Primitive Datatypes}
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Each of the built-in datatypes comes with a set of procedures for
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manipulating members of the datatype.
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@local-table-of-contents[]
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@; ------------------------------------------------------------
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@section[#:tag "booleans"]{Booleans}
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True and false are represented by the values @scheme[#t] and
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@scheme[#f], respectively, though operations that depend a boolean
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value typically treat anything other than @scheme[#f] as true.
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See also: @scheme[and], @scheme[or], @scheme[andmap], @scheme[ormap].
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@defproc[(boolean? [v any/c]) boolean?]{
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Returns @scheme[#t] if @scheme[v] is @scheme[#t] or @scheme[#f],
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@scheme[#f] otherwise.}
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@defproc[(not [v any/c]) boolean?]{
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Returns @scheme[#t] if @scheme[v] is @scheme[#f], @scheme[#f] otherwise.
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}
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@defproc[(equal? [v1 any/c] [v2 any/c]) boolean?]{
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Two values are @scheme[equal?] if and only if they are @scheme[eqv?],
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unless otherwise specified for a particular datatype.
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Datatypes with further specification of @scheme[equal?] include
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strings, byte strings, numbers, pairs, mutable pairs, vectors, hash
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tables, and inspectable structures. In the last five cases, equality
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is recursively defined; if both @scheme[v1] and @scheme[v2] contain
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reference cycles, they are equal when the infinite unfoldings of the
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values would be equal. See also @scheme[prop:equal+hash].}
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@defproc[(eqv? [v1 any/c] [v2 any/c]) boolean?]{
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Two values are @scheme[eqv?] if and only if they are @scheme[eq?],
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unless otherwise specified for a particular datatype.
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The number and character datatypes are the only ones for which
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@scheme[eqv?] differs from @scheme[eq?].}
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@defproc[(eq? [v1 any/c] [v2 any/c]) boolean?]{
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Return @scheme[#t] if @scheme[v1] and @scheme[v2] refer to the same
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object, @scheme[#f] otherwise. See also @secref["model-eq"].}
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@defproc[(immutable? [v any/c]) boolean?]{
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Returns @scheme[#t] if @scheme[v] is an immutable string, byte string,
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vector, or box, @scheme[#f] otherwise.}
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@defthing[prop:equal+hash struct-type-property?]{
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A @tech{structure type property} (see @secref["structprops"]) that
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supplies an equality predicate and hashing functions for a structure
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type. The property value must be a list of three procedures:
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@itemize{
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@item{@scheme[_equal-proc : (any/c any/c (any/c any/c . ->
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. boolean?) . -> . any/c)] --- tests whether the first two
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arguments are equal, where both values are instances of the
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structure type to which the property is associated (or a
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subtype of the structure type).
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The third argument is an @scheme[equal?] predicate to use for
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recursive equality checks; use the given predicate instead of
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@scheme[equal?] to ensure that data cycles are handled
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properly.
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The @scheme[_equal-proc] is called for a pair of structures
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only when they are not @scheme[eq?], and only when they both
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have a @scheme[prop:equal+hash] value inherited from the same
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structure type. With this strategy, the order in which
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@scheme[equal?] receives two structures does not matter. It
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also means that, by default, a structure sub-type inherits the
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equality predicate of its parent, if any.}
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@item{@scheme[_hash-proc : (any/c (any/c . -> . exact-integer?) . ->
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. exact-integer?)] --- computes a hash code for the given
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structure, like @scheme[equal-hash-code]. The first argument is
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an instance of the structure type (or one of its subtypes) to
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which the property is associated.
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The second argument is a @scheme[equal-hash-code]-like
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procedure to use for recursive hash-code computation; use the
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given procedure instead of @scheme[equal-hash-code] to ensure
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that data cycles are handled properly.}
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@item{@scheme[_hash2-proc : (any/c (any/c . -> . exact-integer?) . ->
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. exact-integer?)] --- computes a secondary hash code for the
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given structure. This procedure is like @scheme[_hash-proc],
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but analogous to @scheme[equal-secondary-hash-code].}
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}
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Take care to ensure that @scheme[_hash-proc] and @scheme[_hash2-proc]
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are consistent with @scheme[_equal-proc]. Specifically,
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@scheme[_hash-proc] and @scheme[_hash2-proc] should produce the same
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value for any two structures for which @scheme[_equal-proc] produces a
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true value.
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When a structure type has no @scheme[prop:equal+hash] property, then
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transparent structures (i.e., structures with an @tech{inspector} that
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is controlled by the current @tech{inspector}) are @scheme[equal?]
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when they are instances of the same structure type (not counting
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sub-types), and when they have @scheme[equal?] field values. For
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transparent structures, @scheme[equal-hash-code] and
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@scheme[equal-secondary-hash-code] derive hash code using the field
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values. For opaque structure types, @scheme[equal?] is the same as
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@scheme[eq?], and @scheme[equal-hash-code] and
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@scheme[equal-secondary-hash-code] results are based only on
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@scheme[eq-hash-code].}
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@subsection{Boolean Synonyms}
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@note-lib[scheme/bool]
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@defthing[true boolean?]{A synonym for @scheme[#t].}
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@defthing[false boolean?]{A synonym for @scheme[#f].}
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@defproc[(symbol=? [a symbol?] [b symbol?]) boolean?]{
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Returns @scheme[(equal? a b)].}
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@defproc[(boolean=? [a boolean?] [b boolean?]) boolean?]{
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Returns @scheme[(equal? a b)].}
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@; ------------------------------------------------------------
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@include-section["numbers.scrbl"]
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@; ------------------------------------------------------------
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@include-section["strings.scrbl"]
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@; ------------------------------------------------------------
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@include-section["bytes.scrbl"]
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@; ------------------------------------------------------------
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@include-section["chars.scrbl"]
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@; ------------------------------------------------------------
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@section[#:tag "symbols"]{Symbols}
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@guideintro["symbols"]{symbols}
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@section-index["symbols" "generating"]
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@section-index["symbols" "unique"]
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A symbol is like an immutable string, but symbols are normally
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@deftech{interned}, so that two symbols with the same character
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content are normally @scheme[eq?]. All symbols produced by the default
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reader (see @secref["parse-symbol"]) are interned.
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The two procedures @scheme[string->uninterned-symbol] and
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@scheme[gensym] generate @deftech{uninterned} symbols, i.e., symbols
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that are not @scheme[eq?], @scheme[eqv?], or @scheme[equal?] to any
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other symbol, although they may print the same as other symbols.
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Regular (interned) symbols are only weakly held by the internal symbol
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table. This weakness can never affect the result of an @scheme[eq?],
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@scheme[eqv?], or @scheme[equal?] test, but a symbol may disappear
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when placed into a weak box (see @secref["weakbox"]) used as the key
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in a weak hash table (see @secref["hashtables"]), or used as an
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ephemeron key (see @secref["ephemerons"]).
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@defproc[(symbol? [v any/c]) boolean?]{Returns @scheme[#t] if @scheme[v] is
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a symbol, @scheme[#f] otherwise.}
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@examples[(symbol? 'Apple) (symbol? 10)]
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@defproc[(symbol->string [sym symbol?]) symbol?]{Returns a freshly
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allocated mutable string whose characters are the same as in
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@scheme[sym].}
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@examples[(symbol->string 'Apple)]
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@defproc[(string->symbol [str string?]) symbol?]{Returns an
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@tech{interned} symbol whose characters are the same as in
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@scheme[str].}
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@examples[(string->symbol "Apple") (string->symbol "1")]
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@defproc[(string->uninterned-symbol [str string?]) symbol?]{Like
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@scheme[(string->symbol str)], but the resulting symbol is a new
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@tech{uninterned} symbol. Calling @scheme[string->uninterned-symbol]
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twice with the same @scheme[str] returns two distinct symbols.}
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@examples[(string->uninterned-symbol "Apple") (eq? 'a (string->uninterned-symbol "a"))]
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@defproc[(gensym [base (or/c string? symbol?) "g"]) symbol?]{Returns a
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new @tech{uninterned} symbol with an automatically-generated name. The
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optional @scheme[base] argument is a prefix symbol or string.}
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@examples[(gensym "apple")]
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@; ------------------------------------------------------------
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@include-section["regexps.scrbl"]
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@; ------------------------------------------------------------
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@section[#:tag "keywords"]{Keywords}
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@guideintro["keywords"]{keywords}
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A keyword is like an @tech{interned} symbol, but its printed form
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starts with @litchar{#:}, and a keyword cannot be used as an
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identifier. Furthermore, a keyword by itself is not a valid
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expression, though a keyword can be @scheme[quote]d to form an
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expression that produces the symbol.
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Two keywords are @scheme[eq?] if and only if they print the same.
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Like symbols, keywords are only weakly held by the internal keyword
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table; see @secref["symbols"] for more information.
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@defproc[(keyword? [v any/c]) boolean?]{
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Returns @scheme[#t] if @scheme[v] is a keyword, @scheme[#f] otherwise.}
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@defproc[(keyword->string [keyword keyword?]) string?]{
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Returns a string for the @scheme[display]ed form of @scheme[keyword],
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not including the leading @litchar{#:}.}
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@defproc[(string->keyword [str string?]) keyword]{
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Returns a keyword whose @scheme[display]ed form is the same as that of
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@scheme[str], but with a leading @litchar{#:}.}
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@defproc[(keyword<? [a-keyword keyword?][b-keyword keyword?] ...+) boolean?]{
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Returns @scheme[#t] if the arguments are sorted, where the comparison
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for each pair of keywords is the same as using
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@scheme[keyword->string] and @scheme[string<?].}
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@; ----------------------------------------------------------------------
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@include-section["pairs.scrbl"]
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@; ----------------------------------------------------------------------
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@include-section["mpairs.scrbl"]
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@; ------------------------------------------------------------
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@section[#:tag "vectors"]{Vectors}
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A vector is a fixed-length array with constant-time access and update
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of the vector slots, which are numbered from @scheme[0] to one less
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than the number of slots in the vector.
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Two vectors are @scheme[equal?] if they have the same length, and if
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the values in corresponding slots of the the vectors are
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@scheme[equal?].
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A vector can be @defterm{mutable} or @defterm{immutable}. When an
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immutable vector is provided to a procedure like @scheme[vector-set!],
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the @exnraise[exn:fail:contract]. Vectors generated by the default
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reader (see @secref["parse-string"]) are immutable.
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A vector can be used as a single-valued sequence (see
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@secref["sequences"]). The elements of the vector serve as elements
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of the sequence. See also @scheme[in-vector].
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@defproc[(vector? [v any/c]) boolean?]{
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Returns @scheme[#t] if @scheme[v] is a vector, @scheme[#f] otherwise.}
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@defproc[(make-vector [size nonnegative-exact-integer?]
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[v any/c 0]) vector?]{
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Returns a mutable vector with @scheme[size] slots, where all slots are
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initialized to contain @scheme[v].}
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@defproc[(vector [v any/c] ...) vector?]{
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Returns a mutable vector with as many slots as provided @scheme[v]s,
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where the slots are initialized to contain the given @scheme[v]s in
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order.}
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@defproc[(vector-immutable [v any/c] ...) (and/c vector?
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immutable?)]{
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Returns an immutable vector with as many slots as provided
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@scheme[v]s, where the slots are contain the given @scheme[v]s in
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order.}
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@defproc[(vector-length [vec vector?]) nonnegative-exact-integer?]{
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Returns the length of @scheme[vec] (i.e., the number of slots in the
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vector).}
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@defproc[(vector-ref [vec vector?][pos nonnegative-exact-integer?]) any/c]{
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Returns the element in slot @scheme[pos] of @scheme[vec]. The first
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slot is position @scheme[0], and the last slot is one less than
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@scheme[(vector-length vec)].}
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@defproc[(vector-set! [vec (and/c vector? (not/c immutable?))]
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[pos nonnegative-exact-integer?]
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[v any/c])
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void?]{
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Updates the slot @scheme[pos] of @scheme[vec] to contain @scheme[v].}
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@defproc[(vector->list [vec vector?])
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list?]{
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Returns a list with the same length and elements as @scheme[vec].}
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@defproc[(list->vector [lst list?])
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vector?]{
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Returns a mutable vector with the same length and elements as
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@scheme[lst].}
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@defproc[(vector->immutable-vector [vec vector?])
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(and/c vector? immutable?)]{
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Returns an immutable vector with the same length and elements as @scheme[vec].
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If @scheme[vec] is itself immutable, then it is returned as the result.}
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@defproc[(vector-fill! [vec (and/c vector? (not/c immutable?))]
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[v any/c])
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void?]{
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Changes all slots of @scheme[vec] to contain @scheme[v].}
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@defproc[(vector-copy! [dest (and/c vector? (not/c immutable?))]
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[dest-start exact-nonnegative-integer?]
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[src vector?]
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[src-start exact-nonnegative-integer? 0]
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[src-end exact-nonnegative-integer? (vector-length src)])
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void?]{
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Changes the elements of @scheme[dest] starting at position
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@scheme[dest-start] to match the elements in @scheme[src] from
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@scheme[src-start] (inclusive) to @scheme[src-end] (exclusive). The
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vectors @scheme[dest] and @scheme[src] can be the same vector, and in
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that case the destination region can overlap with the source region;
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the destination elements after the copy match the source elements
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from before the copy. If any of @scheme[dest-start],
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@scheme[src-start], or @scheme[src-end] are out of range (taking into
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account the sizes of the vectors and the source and destination
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regions), the @exnraise[exn:fail:contract].
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@examples[(define v (vector 'A 'p 'p 'l 'e))
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(vector-copy! v 4 #(y))
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(vector-copy! v 0 v 3 4)
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v]}
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@defproc[(vector->values [vec vector?]
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[start-pos nonnegative-exact-integer? 0]
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[end-pos nonnegative-exact-integer? (vector-length vec)])
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any]{
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Returns @math{@scheme[end-pos] - @scheme[start-pos]} values, which are
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the elements of @scheme[vec] from @scheme[start-pos] (inclusive) to
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@scheme[end-pos] (exclusive). If @scheme[start-pos] or
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@scheme[end-pos] are greater than @scheme[(vector-length vec)], or if
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@scheme[end-pos] is less than @scheme[start-pos], the
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@exnraise[exn:fail:contract].}
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@defproc[(build-vector [n exact-nonnegative-integer?]
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[proc (exact-nonnegative-integer? . -> . any.c)])
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vector?]{
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Creates a vector of @scheme[n] elements by applying @scheme[proc] to
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the integers from @scheme[0] to @scheme[(sub1 n)] in order. If
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@scheme[_vec] is the resulting vector, then @scheme[(vector-ref _vec
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_i)] is the value produced by @scheme[(proc _i)].
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@examples[
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(build-vector 5 add1)
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]}
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@; ------------------------------------------------------------
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@section[#:tag "boxes"]{Boxes}
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@defproc[(box? [v any/c]) boolean?]{
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Returns @scheme[#t] if @scheme[v] is a box, @scheme[#f] otherwise.}
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@defproc[(box [v any/c]) box?]{
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Returns a new mutable box that contains @scheme[v].}
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@defproc[(box-immutable [v any/c]) (and/c box? immutable?)]{
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Returns a new immutable box that contains @scheme[v].}
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@defproc[(unbox [box box?]) any/c]{
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Returns the content of @scheme[box]. For any @scheme[v],
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@scheme[(unbox (box @scheme[v]))] returns @scheme[v].}
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@defproc[(set-box! [box (and/c box? (not/c immutable?))]
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[v any/c]) void?]{
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Sets the content of @scheme[box] to @scheme[v].}
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@; ----------------------------------------------------------------------
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@section[#:tag "hashtables"]{Hash Tables}
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A hash table can be used as a two-valued sequence (see
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@secref["sequences"]). The keys and values of the hash table serve
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as elements of the sequence (i.e., each element is a key and its
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associated value). If a mapping is added to or removed from the hash
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table during iteration, then an iteration step may fail with
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@scheme[exn:fail:contract], or the iteration may skip or duplicate
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keys and values. See also @scheme[in-hash-table],
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@scheme[in-hash-table-keys], @scheme[in-hash-table-values], and
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@scheme[in-hash-table-pairs].
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Two hash tables are @scheme[equal?] if they are created with the same
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flags, and if they map the same keys to @scheme[equal?] values (where
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``same key'' means either @scheme[eq?] or @scheme[equal?], depending
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on the way the hash table compares keys).
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@bold{Caveats concerning concurrent modification:} A hash table can be
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manipulated with @scheme[hash-table-get], @scheme[hash-table-put!],
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and @scheme[hash-table-remove!] concurrently by multiple threads, and
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the operations are protected by a table-specific semaphore as
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needed. Two caveats apply, however:
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@itemize{
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@item{If a thread is terminated while applying
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@scheme[hash-table-get], @scheme[hash-table-put!], or
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@scheme[hash-table-remove!] to a hash table that uses
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@scheme[equal?] comparisons, all current and future operations on
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the hash table block indefinitely.}
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@item{The @scheme[hash-table-map], @scheme[hash-table-for-each], and
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@scheme[hash-table-count] procedures do not use the table's
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semaphore. Consequently, if a hash table is extended with new keys
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by another thread while a map, for-each, or count is in process,
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arbitrary key--value pairs can be dropped or duplicated in the map
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or for-each. Similarly, if a map or for-each procedure itself
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extends the table, arbitrary key--value pairs can be dropped or
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duplicated. However, key mappings can be deleted or remapped by any
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thread with no adverse affects (i.e., the change does not affect a
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traversal if the key has been seen already, otherwise the traversal
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skips a deleted key or uses the remapped key's new value).}
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}
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@bold{Caveat concerning mutable keys:} If a key into an
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@scheme[equal?]-based hash table is mutated (e.g., a key string is
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modified with @scheme[string-set!]), then the hash table's behavior
|
|
for put and get operations becomes unpredictable.
|
|
|
|
|
|
@defproc[(hash-table? [v any/c] [flag (one-of/c 'weak 'equal)] ...)
|
|
hash-table?]{
|
|
|
|
Returns @scheme[#t] if @scheme[v] was created by
|
|
@scheme[make-hash-table] or @scheme[make-immutable-hash-table] with
|
|
the given @scheme[flag]s (or more), @scheme[#f] otherwise. Each
|
|
provided @scheme[flag] must be distinct; if the second @scheme[flag]
|
|
is redundant, the @exnraise[exn:fail:contract].}
|
|
|
|
|
|
@defproc[(make-hash-table [flag (one-of/c 'weak 'equal)] ...)
|
|
hash-table?]{
|
|
|
|
Creates and returns a new hash table. If provided, each @scheme[flag]
|
|
must one of the following:
|
|
|
|
@itemize{
|
|
|
|
@item{@indexed-scheme['weak] --- creates a hash table with weakly-held
|
|
keys (see @secref["weakbox"]).}
|
|
|
|
@item{@indexed-scheme['equal] --- creates a hash table that compares
|
|
keys using @scheme[equal?] instead of @scheme[eq?] (needed, for
|
|
example, when using strings as keys).}
|
|
|
|
}
|
|
|
|
By default, key comparisons use @scheme[eq?]. If the second
|
|
@scheme[flag] is redundant, the @exnraise[exn:fail:contract].}
|
|
|
|
|
|
@defproc[(make-immutable-hash-table [assocs (listof pair?)]
|
|
[flag (one-of/c 'equal)]
|
|
...)
|
|
(and/c hash-table? immutable?)]{
|
|
|
|
Creates an immutable hash table. In each element of @scheme[assocs],
|
|
the @scheme[car] of each pair is a key, and the @scheme[cdr] is the
|
|
corresponding value. The mappings are added to the table in the order
|
|
that they appear in @scheme[assocs], so later mappings can hide
|
|
earlier mappings. If the optional @scheme[flag] argument is provided,
|
|
it must be @scheme['equal], and the created hash table compares keys
|
|
with @scheme[equal?]; otherwise, the created table compares keys with
|
|
@scheme[eq?].}
|
|
|
|
|
|
@defproc[(hash-table-put! [hash-table (and/c hash-table?
|
|
(not/c immutable?))]
|
|
[key any/c]
|
|
[v any/c]) void?]{
|
|
|
|
Maps @scheme[key] to @scheme[v] in @scheme[hash-table], overwriting
|
|
any existing mapping for @scheme[key].}
|
|
|
|
@defproc[(hash-table-get [hash-table hash-table?]
|
|
[key any/c]
|
|
[failure-result any/c (lambda () (raise (make-exn:fail ....)))])
|
|
any]{
|
|
|
|
Returns the value for @scheme[key] in @scheme[hash-table]. If no value
|
|
is found for @scheme[key], then @scheme[failure-result] determines the
|
|
result:
|
|
|
|
@itemize{
|
|
|
|
@item{If @scheme[failure-result] is a procedure, it is called
|
|
(through a tail call) with no arguments to produce the result.}
|
|
|
|
@item{Otherwise, @scheme[failure-result] is returned as the result.}
|
|
|
|
}}
|
|
|
|
|
|
@defproc[(hash-table-remove! [hash-table (and/c hash-table?
|
|
(not/c immutable?))]
|
|
[key any/c])
|
|
void?]{
|
|
|
|
Removes any existing mapping for @scheme[key] in @scheme[hash-table].}
|
|
|
|
|
|
@defproc[(hash-table-map [hash-table hash-table?]
|
|
[proc (any/c any/c . -> . any/c)])
|
|
(listof any/c)]{
|
|
|
|
Applies the procedure @scheme[proc] to each element in
|
|
@scheme[hash-table] in an unspecified order, accumulating the results
|
|
into a list. The procedure @scheme[proc] is called each time with a
|
|
key and its value. See the caveat above about concurrent
|
|
modification.}
|
|
|
|
|
|
@defproc[(hash-table-for-each [hash-table hash-table?]
|
|
[proc (any/c any/c . -> . any)])
|
|
void?]{
|
|
|
|
Applies @scheme[proc] to each element in @scheme[hash-table] (for the
|
|
side-effects of @scheme[proc]) in an unspecified order. The procedure
|
|
@scheme[proc] is called each time with a key and its value. See the
|
|
caveat above about concurrent modification.}
|
|
|
|
|
|
@defproc[(hash-table-count [hash-table hash-table?])
|
|
nonnegative-exact-integer?]{
|
|
|
|
Returns the number of keys mapped by @scheme[hash-table]. If
|
|
@scheme[hash-table] is not created with @scheme['weak], then the
|
|
result is computed in constant time and atomically. If
|
|
@scheme[hash-table] is created with @scheme['weak], see the caveat
|
|
above about concurrent modification.}
|
|
|
|
|
|
@defproc[(hash-table-iterate-first [hash-table hash-table?])
|
|
(o/c false/c nonnegative-exact-integer?)]{
|
|
|
|
Returns @scheme[#f] if @scheme[hash-table] contains no elements,
|
|
otherwise it returns an integer that is a index to the first element
|
|
in the hash table; ``first'' refers to an unspecified ordering of the
|
|
table elements, and the index values are not necessarily consecutive
|
|
integers. This index is guaranteed to refer to the first item only as
|
|
long as no items are added to or removed from @scheme[hash-table].}
|
|
|
|
@defproc[(hash-table-iterate-next [hash-table hash-table?]
|
|
[prev nonnegative-exact-integer?])
|
|
(o/c false/c nonnegative-exact-integer?)]{
|
|
|
|
Returns either an integer that is an index to the element in
|
|
@scheme[hash-table] after the element indexed by @scheme[pos] (which
|
|
is not necessarily one more than @scheme[pos]) or @scheme[#f] if
|
|
@scheme[pos] refers to the last element in @scheme[hash-table]. If
|
|
@scheme[pos] is not a valid index, then the
|
|
@exnraise[exn:fail:contract]. The result index is guaranteed to refer
|
|
to its item only as long as no items are added to or removed from
|
|
@scheme[hash-table].}
|
|
|
|
|
|
@defproc[(hash-table-iterate-key [hash-table hash-table?]
|
|
[pos nonnegative-exact-integer?])
|
|
any]{
|
|
|
|
Returns the key for the element in @scheme[hash-table] at index
|
|
@scheme[pos]. If @scheme[pos] is not a valid index for
|
|
@scheme[hash-table], the @exnraise[exn:fail:contract].}
|
|
|
|
|
|
@defproc[(hash-table-iterate-value [hash-table hash-table?]
|
|
[pos nonnegative-exact-integer?])
|
|
any]{
|
|
|
|
Returns the value for the element in @scheme[hash-table] at index
|
|
@scheme[pos]. If @scheme[pos] is not a valid index for
|
|
@scheme[hash-table], the @exnraise[exn:fail:contract].}
|
|
|
|
|
|
@defproc[(hash-table-copy [hash-table hash-table?])
|
|
(and/c hash-table?
|
|
(not/c immutable?))]{
|
|
|
|
Returns a mutable hash table with the same mappings, same
|
|
key-comparison mode, and same key-holding strength as
|
|
@scheme[hash-table].}
|
|
|
|
|
|
@defproc[(eq-hash-code [v any/c]) exact-integer?]{
|
|
|
|
Returns an exact integer; for any two @scheme[eq?] values, the
|
|
returned integer is the same. Furthermore, for the result integer
|
|
@scheme[k] and any other exact integer @scheme[j], @scheme[(= k j)]
|
|
implies @scheme[(eq? k j)].}
|
|
|
|
|
|
@defproc[(equal-hash-code [v any/c]) exact-integer?]{
|
|
|
|
Returns an exact integer; for any two @scheme[equal?] values, the
|
|
returned integer is the same. Furthermore, for the result integer
|
|
@scheme[k] and any other exact integer @scheme[j], @scheme[(= k j)]
|
|
implies @scheme[(eq? k j)]. A has code is computed even when
|
|
@scheme[v] contains a cycle through pairs, vectors, boxes, and/or
|
|
inspectable structure fields. See also @scheme[prop:equal+hash].}
|
|
|
|
@defproc[(equal-secondary-hash-code [v any/c]) exact-integer?]{
|
|
|
|
Like @scheme[equal-hash-code], but computes a secondary value suitable
|
|
for use in double hashing.}
|
|
|
|
@; ----------------------------------------------------------------------
|
|
@include-section["sequences.scrbl"]
|
|
|
|
@; ----------------------------------------------------------------------
|
|
@include-section["procedures.scrbl"]
|
|
|
|
@; ----------------------------------------------------------------------
|
|
@section[#:tag "void"]{Void and Undefined}
|
|
|
|
The constant @|void-const| is returned by most forms and procedures
|
|
that have a side-effect and no useful result. The constant
|
|
@|undefined-const| is used as the initial value for @scheme[letrec]
|
|
bindings.
|
|
|
|
@defproc[(void? [v any/c]) void?]{Returns @scheme[#t] if @scheme[v] is the
|
|
constant @|void-const|, @scheme[#f] otherwise.}
|
|
|
|
|
|
@defproc[(void [v any/c] ...) void?]{Returns the constant @|void-const|. Each
|
|
@scheme[v] argument is ignored.}
|
|
|