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4.9 Hash tables

There are many mutable hashtable APIs amongst all the various Scheme implementations, standards, and SRFIs. From our point of view, there is no clear “best” hashtable API that has emerged, but we think the R6RS interface is OK. Guile’s own hashtable API has design issues that are best left in the past. So, the (hoot hashtables) module is R6RS-like.

Currently, this interface supports keys hashed by object identity (eq?) only. The object equivalence (eqv?) and deep object equality (equal?) hashing strategies are not yet implemented.

Procedure: make-eq-hashtable ¶

Return a new, empty hash table.

Procedure: hashtable? obj ¶

Return #t if obj

Procedure: hashtable-size hashtable ¶

Return the number of key/value pairs in hashtable.

Procedure: hashtable-ref hashtable key default ¶

Return the value associated with key in hashtable or default if there is no such association.

Procedure: hashtable-set! hashtable key value ¶

Modify hashtable to associate key with value, overwriting any previous association that may have existed.

Procedure: hashtable-delete! hashtable key ¶

Remove the association with key in hashtable, if one exists.

Procedure: hashtable-clear! hashtable ¶

Remove all of the key/value associations in hashtable.

Procedure: hashtable-contains? hashtable key ¶

Return #t if key has an associated value in hashtable.

Procedure: hashtable-copy hashtable ¶

Return a copy of hashtable.

Procedure: hashtable-keys hashtable ¶

Return a vector of keys in hashtable.

Procedure: hashtable-entries hashtable ¶

Return a vector of values in hashtable.

Procedure: hashtable-for-each proc hashtable ¶

For each key/value pair in hashtable, call proc with two arguments: the key and the value.

Hoot also includes weak key hash tables that wrap those of the Wasm host platform, such as the WeakMap JavaScript class on the web.

Procedure: make-weak-key-hashtable ¶

Return a new weak key hashtable.

Procedure: weak-key-hashtable? obj ¶

Return #t if obj is a weak key hashtable.

Procedure: weak-key-hashtable-ref hashtable key [default #f] ¶

Return the value associated with key in hashtable or default if there is no such association.

Procedure: weak-key-hashtable-set! hashtable key value ¶

Modify hashtable to associate key with value, overwriting any previous association that may have existed.

Procedure: weak-key-hashtable-delete! hashtable key ¶

Remove the association with key in hashtable, if one exists.

The underlying hash functions are also available.

Procedure: hashq key size ¶

Return a hash value for key suitable for using in a table containing size buckets. The returned hash value will be in the range [0, size).