7.1.12 Hash Tables

(require 'hash-table)

Function: predicate->hash pred

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

A hash table is a vector of association lists.

Function: make-hash-table k

Returns a vector of k empty (association) lists.

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

Function: predicate->hash-asso pred

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

Function: hash-inquirer pred

Returns a procedure of 2 arguments, hashtab and key, which returns the value associated with key in hashtab or #f if key does not appear in hashtab.

Function: hash-associator pred

Returns a procedure of 3 arguments, hashtab, key, and value, which modifies hashtab so that key and value associated. Any previous value associated with key will be lost.

Function: hash-remover pred

Returns a procedure of 2 arguments, hashtab and key, which modifies hashtab so that the association whose key is key is removed.

Function: hash-map proc hash-table

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

Function: hash-for-each proc hash-table

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

Function: hash-rehasher pred

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

This function is used for nondestrutively resizing a hash table. hashtab should be an existing hash-table using pred, 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.