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4.9 Hashtables

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 but with some notable differences.

Procedure: make-hashtable [hash hash] [equiv equal?] ¶

Return a new, empty hashtable that uses the hash procedure hash and equivalence procedure equiv.

Procedure: make-eq-hashtable ¶

Return a new, empty hashtable that uses eq? as the equivalence function and hashes keys accordingly.

Procedure: make-eqv-hashtable ¶

Return a new, empty hashtable that uses eqv? as the equivalence function and hashes keys accordingly.

Procedure: hashtable? obj ¶

Return #t if obj

Procedure: hashtable-hash table ¶

Return the hash function for table.

Procedure: hashtable-equiv table ¶

Return the equivalence function for table.

Procedure: hashtable-size table ¶

Return the current number of key/value pairs in table.

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

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

Procedure: hashtable-set! table key value ¶

Associate val with key in table, potentially overwriting any previous association with key.

Procedure: hashtable-delete! table key ¶

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

Procedure: hashtable-clear! table ¶

Remove all of the key/value associations in table.

Procedure: hashtable-contains? table key ¶

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

Procedure: hashtable-copy table ¶

Return a copy of table.

Procedure: hashtable-keys table ¶

Return a list of keys in table.

Procedure: hashtable-values table ¶

Return a list of values in table.

Procedure: hashtable-for-each proc table ¶

Apply proc to each key/value association in table. Each call is of the form (proc key value).

Procedure: hashtable-fold proc init table ¶

Accumulate a result by applying proc with each key/value association in table and the result of the previous proc call. Each call is of the form (proc key value prev). For the first call, prev is the initial value init.

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 following hash functions are available:

Procedure: hash key size ¶

Procedure: hashq key size ¶

Procedure: hashv 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).

hashq is the hash function used by make-eq-hashtable, and hashv is used by make-eqv-hashtable.