Hash Tables

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

•   (make-hash-table) creates and returns a new hash table.
  item (make-hash-table-weak) creates a hash table with weakly-held keys (see section 2.21).
•   (hash-table? v) returns #t if v was created by make-hash-table or #f otherwise.
•   (hash-table-put! table key value) puts the specified value in the table, overwriting any existing assignments for the key.
•   (hash-table-get table key failure-thunk) gets the value for the specified key. If no value is found for key, then failure-thunk is invoked. The failure-thunk argument is optional; if it is not specified, the  exn:misc:hash-table exception is raised when no value is found for key.
•   (hash-table-remove! table key) removes the value assignment of key if it exists in the 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 a 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 a value.