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(elisp)Association List Type

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Association List Type
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   An "association list" or "alist" is a specially-constructed list
whose elements are cons cells.  In each element, the CAR is considered
a "key", and the CDR is considered an "associated value".  (In some
cases, the associated value is stored in the CAR of the CDR.)
Association lists are often used as stacks, since it is easy to add or
remove associations at the front of the list.

   For example,

     (setq alist-of-colors
           '((rose . red) (lily . white) (buttercup . yellow)))

sets the variable `alist-of-colors' to an alist of three elements.  In
the first element, `rose' is the key and `red' is the value.

   Note: Association Lists, for a further explanation of alists and
for functions that work on alists.  Note: Hash Tables, for another
kind of lookup table, which is much faster for handling a large number
of keys.