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! hash-table key-v v) maps key-v to v in hash-table, overwriting any existing mapping for key-v.
• (hash-table-get hash-table key-v [failure-thunk]) returns the value for key-v in hash-table. If no value is found for key-v, then the result of invoking failure-thunk (a procedure of no arguments) is returned. If failure-thunk is not provided, the exn:application:mismatch exception is raised if no value is found for key-v.
• (hash-table-remove! hash-table key-v) removes the value mapping for key-v if it exists in hash-table.
• (hash-table-map hash-table proc) applies the procedure proc to each element in hash-table, accumulating the results into a list. The procedure proc must take two arguments: a key and its value.
• (hash-table-for-each hash-table proc) applies the procedure proc to each element in hash-table (for the side-effects of proc) and returns void. The procedure proc must take two arguments: a key and its value.