diff --git a/doc/ref/scheme-compound.texi b/doc/ref/scheme-compound.texi index b8ab32ecb..447d96249 100644 --- a/doc/ref/scheme-compound.texi +++ b/doc/ref/scheme-compound.texi @@ -2245,238 +2245,177 @@ a hash table, but @code{hash-fold} can be used for doing exactly that. @node Hash Table Reference @subsubsection Hash Table Reference -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?}. +@c FIXME: Describe in broad terms what happens for resizing, and what +@c the initial size means for this. -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. +Like the association list functions, the hash table functions come in +several varieties, according to the equality test used for the keys. +Plain @code{hash-} functions use @code{equal?}, @code{hashq-} +functions use @code{eq?}, @code{hashv-} functions use @code{eqv?}, and +the @code{hashx-} functions use an application supplied test (for +instance to implement case insensitive strings). -@deffn {Scheme Procedure} make-hash-table size -Create a new hash table of @var{size} slots. Note that the number of -slots does not limit the size of the table, it just tells how large -the underlying vector will be. The @var{size} should be similar to -the expected number of elements which will be added to the table, but -they need not match. For good performance, it might be a good idea to -use a prime number as the @var{size}. -@end deffn +A single @code{make-hash-table} creates a hash table suitable for use +with any set of functions, but it's imperative that just one set is +then used consistently, or results will be unpredictable. -@deffn {Scheme Procedure} hashq-ref table key [dflt] -@deffnx {C Function} scm_hashq_ref (table, key, 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 @code{eq?} for equality testing. -@end deffn +@sp 1 +Hash tables are implemented as a vector indexed by an integer formed +from the key, with an association list of key/value pairs for each +bucket in case distinct keys hash together. Direct access to the +pairs in those lists is provided by the @code{-handle-} functions. -@deffn {Scheme Procedure} hashv-ref table key [dflt] -@deffnx {C Function} scm_hashv_ref (table, key, 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 @code{eqv?} for equality testing. +For the @code{hashx-} ``extended'' routines, an application supplies a +@var{hash} function producing an integer index (like @code{hashq} etc +below), and an @var{assoc} alist search function (like @code{assq} +etc, @xref{Retrieving Alist Entries}.). The aim in the @var{hash} +function is to have different keys spread out across the vector, so +the bucket lists don't become long, but the exact values generated are +otherwise arbitrary. + +@sp 1 +@deffn {Scheme Procedure} make-hash-table [size] +Create a new hash table, with an optional initial vector @var{size}. + +@var{size} doesn't limit the entries in the table, merely gives a +starting size for the internal vector. A prime number bigger than the +expected number of entries would be a good choice. @end deffn @deffn {Scheme Procedure} hash-ref table key [dflt] +@deffnx {Scheme Procedure} hashq-ref table key [dflt] +@deffnx {Scheme Procedure} hashv-ref table key [dflt] +@deffnx {Scheme Procedure} hashx-ref hash assoc table key [dflt] @deffnx {C Function} scm_hash_ref (table, key, 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 @code{equal?} for equality testing. -@end deffn - -@deffn {Scheme Procedure} hashq-set! table key val -@deffnx {C Function} scm_hashq_set_x (table, key, val) -Find the entry in @var{table} associated with @var{key}, and -store @var{value} there. Uses @code{eq?} for equality testing. -@end deffn - -@deffn {Scheme Procedure} hashv-set! table key val -@deffnx {C Function} scm_hashv_set_x (table, key, val) -Find the entry in @var{table} associated with @var{key}, and -store @var{value} there. Uses @code{eqv?} for equality testing. +@deffnx {C Function} scm_hashq_ref (table, key, dflt) +@deffnx {C Function} scm_hashv_ref (table, key, dflt) +@deffnx {C Function} scm_hashx_ref (hash, assoc, table, key, dflt) +Lookup @var{key} in the given hash @var{table}, and return the +associated value. If @var{key} is not found, return @var{dflt}, or +@code{#f} if @var{dflt} is not given. (For the C functions, +@var{dflt} must be given.) @end deffn @deffn {Scheme Procedure} hash-set! table key val +@deffnx {Scheme Procedure} hashq-set! table key val +@deffnx {Scheme Procedure} hashv-set! table key val +@deffnx {Scheme Procedure} hashx-set! hash assoc table key val @deffnx {C Function} scm_hash_set_x (table, key, val) -Find the entry in @var{table} associated with @var{key}, and -store @var{value} there. Uses @code{equal?} for equality -testing. -@end deffn - -@deffn {Scheme Procedure} hashq-remove! table key -@deffnx {C Function} scm_hashq_remove_x (table, key) -Remove @var{key} (and any value associated with it) from -@var{table}. Uses @code{eq?} for equality tests. -@end deffn - -@deffn {Scheme Procedure} hashv-remove! table key -@deffnx {C Function} scm_hashv_remove_x (table, key) -Remove @var{key} (and any value associated with it) from -@var{table}. Uses @code{eqv?} for equality tests. +@deffnx {C Function} scm_hashq_set_x (table, key, val) +@deffnx {C Function} scm_hashv_set_x (table, key, val) +@deffnx {C Function} scm_hashx_set_x (hash, assoc, table, key, val) +Associate @var{val} with @var{key} in the given hash @var{table}. If +@var{key} is already present then it's associated value is changed. +If it's not present then a new entry is created. @end deffn @deffn {Scheme Procedure} hash-remove! table key +@deffnx {Scheme Procedure} hashq-remove! table key +@deffnx {Scheme Procedure} hashv-remove! table key @deffnx {C Function} scm_hash_remove_x (table, key) -Remove @var{key} (and any value associated with it) from -@var{table}. Uses @code{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. - -@deffn {Scheme Procedure} hashq key size -@deffnx {C Function} scm_hashq (key, size) -Determine a hash value for @var{key} that is suitable for -lookups in a hash table of size @var{size}, where @code{eq?} is -used as the equality predicate. The function returns an -integer in the range 0 to @var{size} - 1. Note that -@code{hashq} may use internal addresses. Thus two calls to -hashq where the keys are @code{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: -@code{(hashq 'foo n) (gc) (hashq 'foo n)} may produce two -different values, since @code{foo} will be garbage collected. -@end deffn - -@deffn {Scheme Procedure} hashv key size -@deffnx {C Function} scm_hashv (key, size) -Determine a hash value for @var{key} that is suitable for -lookups in a hash table of size @var{size}, where @code{eqv?} is -used as the equality predicate. The function returns an -integer in the range 0 to @var{size} - 1. Note that -@code{(hashv key)} may use internal addresses. Thus two calls -to hashv where the keys are @code{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: -@code{(hashv 'foo n) (gc) (hashv 'foo n)} may produce two -different values, since @code{foo} will be garbage collected. +@deffnx {C Function} scm_hashq_remove_x (table, key) +@deffnx {C Function} scm_hashv_remove_x (table, key) +Remove any association for @var{key} in the given hash @var{table}. +If @var{key} is not in @var{table} then nothing is done. @end deffn @deffn {Scheme Procedure} hash key size +@deffnx {Scheme Procedure} hashq key size +@deffnx {Scheme Procedure} hashv key size @deffnx {C Function} scm_hash (key, size) -Determine a hash value for @var{key} that is suitable for -lookups in a hash table of size @var{size}, where @code{equal?} -is used as the equality predicate. The function returns an -integer in the range 0 to @var{size} - 1. -@end deffn +@deffnx {C Function} scm_hashq (key, size) +@deffnx {C Function} scm_hashv (key, size) +Return a hash value for @var{key}. This is a number in the range +@math{0} to @math{@var{size}-1}, which is suitable for use in a hash +table of the given @var{size}. -@deffn {Scheme Procedure} hashx-ref hash assoc table key [dflt] -@deffnx {C Function} scm_hashx_ref (hash, assoc, table, key, dflt) -This behaves the same way as the corresponding @code{ref} -function, but uses @var{hash} as a hash function and -@var{assoc} to compare keys. @code{hash} 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}. +Note that @code{hashq} and @code{hashv} may use internal addresses of +objects, so if an object is garbage collected and re-created it can +have a different hash value, even when the two are notionally +@code{eq?}. For instance with symbols, -By way of illustration, @code{hashq-ref table key} is -equivalent to @code{hashx-ref hashq assq table key}. -@end deffn +@example +(hashq 'something 123) @result{} 19 +(gc) +(hashq 'something 123) @result{} 62 +@end example -@deffn {Scheme Procedure} hashx-set! hash assoc table key val -@deffnx {C Function} scm_hashx_set_x (hash, assoc, table, key, val) -This behaves the same way as the corresponding @code{set!} -function, but uses @var{hash} as a hash function and -@var{assoc} to compare keys. @code{hash} 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 - -@deffn {Scheme Procedure} hashq-get-handle table key -@deffnx {C Function} scm_hashq_get_handle (table, key) -This procedure returns the @code{(key . value)} pair from the -hash table @var{table}. If @var{table} does not hold an -associated value for @var{key}, @code{#f} is returned. -Uses @code{eq?} for equality testing. -@end deffn - -@deffn {Scheme Procedure} hashv-get-handle table key -@deffnx {C Function} scm_hashv_get_handle (table, key) -This procedure returns the @code{(key . value)} pair from the -hash table @var{table}. If @var{table} does not hold an -associated value for @var{key}, @code{#f} is returned. -Uses @code{eqv?} for equality testing. +In normal use this is not a problem, since an object entered into a +hash table won't be garbage collected until removed. It's only if +hashing calculations are somehow separated from normal references that +its lifetime needs to be considered. @end deffn @deffn {Scheme Procedure} hash-get-handle table key +@deffnx {Scheme Procedure} hashq-get-handle table key +@deffnx {Scheme Procedure} hashv-get-handle table key +@deffnx {Scheme Procedure} hashx-get-handle hash assoc table key @deffnx {C Function} scm_hash_get_handle (table, key) -This procedure returns the @code{(key . value)} pair from the -hash table @var{table}. If @var{table} does not hold an -associated value for @var{key}, @code{#f} is returned. -Uses @code{equal?} for equality testing. -@end deffn - -@deffn {Scheme Procedure} hashx-get-handle hash assoc table key +@deffnx {C Function} scm_hashq_get_handle (table, key) +@deffnx {C Function} scm_hashv_get_handle (table, key) @deffnx {C Function} scm_hashx_get_handle (hash, assoc, table, key) -This behaves the same way as the corresponding -@code{-get-handle} function, but uses @var{hash} as a hash -function and @var{assoc} to compare keys. @code{hash} 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 - -@deffn {Scheme Procedure} hashq-create-handle! table key init -@deffnx {C Function} scm_hashq_create_handle_x (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 - -@deffn {Scheme Procedure} hashv-create-handle! table key init -@deffnx {C Function} scm_hashv_create_handle_x (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}. +Return the @code{(@var{key} . @var{value})} pair for @var{key} in the +given hash @var{table}, or @code{#f} if @var{key} is not in +@var{table}. @end deffn @deffn {Scheme Procedure} hash-create-handle! table key init +@deffnx {Scheme Procedure} hashq-create-handle! table key init +@deffnx {Scheme Procedure} hashv-create-handle! table key init +@deffnx {Scheme Procedure} hashx-create-handle! hash assoc table key init @deffnx {C Function} scm_hash_create_handle_x (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}. +@deffnx {C Function} scm_hashq_create_handle_x (table, key, init) +@deffnx {C Function} scm_hashv_create_handle_x (table, key, init) +@deffnx {C Function} scm_hashx_create_handle_x (hash, assoc, table, key, init) +Return the @code{(@var{key} . @var{value})} pair for @var{key} in the +given hash @var{table}. If @var{key} is not in @var{table} then +create an entry for it with @var{init} as the value, and return that +pair. @end deffn -@deffn {Scheme Procedure} hashx-create-handle! hash assoc table key init -@deffnx {C Function} scm_hashx_create_handle_x (hash, assoc, table, key, init) -This behaves the same way as the corresponding -@code{-create-handle} function, but uses @var{hash} as a hash -function and @var{assoc} to compare keys. @code{hash} 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}. +@deffn {Scheme Procedure} hash-map proc table +@deffnx {Scheme Procedure} hash-for-each proc table +@deffnx {C Function} scm_hash_map (proc, table) +@deffnx {C Function} scm_hash_for_each (proc, table) +Apply @var{proc} to the entries in the given hash @var{table}. Each +call is @code{(@var{proc} @var{key} @var{value})}. @code{hash-map} +returns a list of the results from these calls, @code{hash-for-each} +discards the results and returns unspecified value. + +Calls are made over the table entries in an unspecified order, and for +@code{hash-map} the order of the values in the returned list is +unspecified. Results will be unpredictable if @var{table} is modified +while iterating. + +For example the following returns a new alist comprising all the +entries from @code{mytable}, in no particular order. + +@example +(hash-map cons mytable) +@end example @end deffn @deffn {Scheme Procedure} hash-fold proc init table @deffnx {C Function} scm_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. +Accumulate a result by applying @var{proc} to the elements of the +given hash @var{table}. Each call is @code{(@var{proc} @var{key} +@var{value} @var{prior-result})}, where @var{key} and @var{value} are +from the @var{table} and @var{prior-result} is the return from the +previous @var{proc} call. For the first call, @var{prior-result} is +the given @var{init} value. + +Calls are made over the table entries in an unspecified order. +Results will be unpredictable if @var{table} is modified while +@code{hash-fold} is running. + +For example, the following returns a count of how many keys in +@code{mytable} are strings. + +@example +(hash-fold (lambda (key value prior) + (if (string? key) (1+ prior) prior)) + 0 mytable) +@end example @end deffn