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IMHO, it is also important to have a query mechanism to know the comparison and hash criteria of a given hash table. Something like hash-table-type which returns a clue so that you can know at least the given hash table uses which one of system-builtin criteria (e.g. eq?, eqv?, equal?, string, string-ci, ...) or some user-defined custom functions. A function to query a hash table's comparison/hash functions may be acceptable if the default hashtables (created by make-symbol-hash-table etc.) are guaranteed to return functions which are eq? to the known functions (e.g. make-string-hash-table to return string=? as comparison and string-hash as hash). It is necessary when you want to get some external representation of a hash table, for example, a marshalizer to send a Scheme structure over the network. Such a function probably can't deal with hashtables with arbitrary comparison/hash functions, but it is still pretty useful if it deals with standard hashtables. Without the query mechanism, such a function can do nothing but abort when it sees a hash table. hash-table->list won't help. --shiro