Hash Tables

MzScheme provides efficient built-in hash tables. Key comparisons use eq?.

• (make-hash-table) creates and returns a new hash table.
• (make-hash-table-weak) creates a hash table with weakly-held keys (see section 12.1).
• (hash-table? v) returns #t if v was created by make-hash-table or make-hash-table-weak, #f otherwise.
• (hash-table-put! table key value) maps key to value in table, overwriting any existing mapping for key.
• (hash-table-get table key [failure-thunk]) returns the value for key in table. If no value is found for key, then the result of invoking failure-thunk (a procedure of no argments) is returned. If failure-thunk is not provided, the exn:misc:hash-table exception is raised if no value is found for key.
• (hash-table-remove! table key) removes the value mapping for key if it exists in table.
• (hash-table-map table f) applies the procedure f to each element in table, accumulating the results into a list. The procedure f must take two arguments: a key and its value.
• (hash-table-for-each table f) applies the procedure f to each element in table (for the side-effects of f) and returns void. The procedure f must take two arguments: a key and its value.