hashtab.txi

@code{(require 'hash-table)}
@ftindex hash-table


@defun predicate->hash pred

Returns a hash function (like @code{hashq}, @code{hashv}, or
@code{hash}) corresponding to the equality predicate @var{pred}.
@var{pred} should be @code{eq?}, @code{eqv?}, @code{equal?}, @code{=},
@code{char=?}, @code{char-ci=?}, @code{string=?}, or
@code{string-ci=?}.
@end defun

@noindent
A hash table is a vector of association lists.


@defun make-hash-table k

Returns a vector of @var{k} empty (association) lists.
@end defun

@noindent
Hash table functions provide utilities for an associative database.
These functions take an equality predicate, @var{pred}, as an argument.
@var{pred} should be @code{eq?}, @code{eqv?}, @code{equal?}, @code{=},
@code{char=?}, @code{char-ci=?}, @code{string=?}, or
@code{string-ci=?}.


@defun predicate->hash-asso pred

Returns a hash association function of 2 arguments, @var{key} and
@var{hashtab}, corresponding to @var{pred}.  The returned function
returns a key-value pair whose key is @var{pred}-equal to its first
argument or @code{#f} if no key in @var{hashtab} is @var{pred}-equal to
the first argument.
@end defun


@defun hash-inquirer pred

Returns a procedure of 2 arguments, @var{hashtab} and @var{key}, which
returns the value associated with @var{key} in @var{hashtab} or
@code{#f} if @var{key} does not appear in @var{hashtab}.
@end defun


@defun hash-associator pred

Returns a procedure of 3 arguments, @var{hashtab}, @var{key}, and
@var{value}, which modifies @var{hashtab} so that @var{key} and
@var{value} associated.  Any previous value associated with @var{key}
will be lost.
@end defun


@defun hash-remover pred

Returns a procedure of 2 arguments, @var{hashtab} and @var{key}, which
modifies @var{hashtab} so that the association whose key is @var{key} is
removed.
@end defun


@defun hash-map proc hash-table

Returns a new hash table formed by mapping @var{proc} over the
keys and values of @var{hash-table}.  @var{proc} must be a function of 2
arguments which returns the new value part.
@end defun


@defun hash-for-each proc hash-table

Applies @var{proc} to each pair of keys and values of @var{hash-table}.
@var{proc} must be a function of 2 arguments.  The returned value is
unspecified.
@end defun


@defun hash-rehasher pred

@code{hash-rehasher} accepts a hash table predicate and returns a function of two
arguments @var{hashtab} and @var{new-k} which is specialized for
that predicate.

This function is used for nondestrutively resizing a hash table.
@var{hashtab} should be an existing hash-table using @var{pred}, @var{new-k}
is the size of a new hash table to be returned.  The new hash table
will have all of the associations of the old hash table.
@end defun