maphash

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ANSI Common Lisp 18 Hash Tables 18.2 Dictionary of Hash Tables

18.2.11 maphash Function

Syntax:

maphash function hash-table nil

Arguments and Values:

function - a designator for a function of two arguments, the key and the value.

hash-table - a hash table.

Description:

Iterates over all entries in the hash-table. For each entry, the function is called with two arguments--the key and the value of that entry.

The consequences are unspecified if any attempt is made to add or remove an entry from the hash-table while a maphash is in progress, with two exceptions: the function can use can use setf of gethash to change the value part of the entry currently being processed, or it can use remhash to remove that entry.

Examples:

 (setq table (make-hash-table)) #<HASH-TABLE EQL 0/120 32304110>
 (dotimes (i 10) (setf (gethash i table) i)) NIL
 (let ((sum-of-squares 0))
 (maphash #'(lambda (key val) 
 (let ((square (* val val)))
 (incf sum-of-squares square)
 (setf (gethash key table) square)))
 table)
 sum-of-squares) 285
 (hash-table-count table) 10
 (maphash #'(lambda (key val)
 (when (oddp val) (remhash key table)))
 table) NIL
 (hash-table-count table) 5
 (maphash #'(lambda (k v) (print (list k v))) table)
(0 0) 
(8 64) 
(2 4) 
(6 36) 
(4 16) 
 NIL

Side Effects:

None, other than any which might be done by the function.

Allegro CL Implementation Details:

None.

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