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(cl)Association Lists

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Association Lists
=================

An "association list" is a list representing a mapping from one set of
values to another; any list whose elements are cons cells is an
association list.

 - Function: assoc* item a-list &key :test :test-not :key
     This function searches the association list A-LIST for an element
     whose `car' matches (in the sense of `:test', `:test-not', and
     `:key', or by comparison with `eql') a given ITEM.  It returns the
     matching element, if any, otherwise `nil'.  It ignores elements of
     A-LIST which are not cons cells.  (This corresponds to the
     behavior of `assq' and `assoc' in Emacs Lisp; Common Lisp's
     `assoc' ignores `nil's but considers any other non-cons elements
     of A-LIST to be an error.)

 - Function: rassoc* item a-list &key :test :test-not :key
     This function searches for an element whose `cdr' matches ITEM.
     If A-LIST represents a mapping, this applies the inverse of the
     mapping to ITEM.

   The `assoc-if', `assoc-if-not', `rassoc-if', and `rassoc-if-not'
functions are defined similarly.

   Two simple functions for constructing association lists are:

 - Function: acons key value alist
     This is equivalent to `(cons (cons KEY VALUE) ALIST)'.

 - Function: pairlis keys values &optional alist
     This is equivalent to `(nconc (mapcar* 'cons KEYS VALUES) ALIST)'.


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