assoc0.html

Association lists are a simple key/value data structure, consisting of a list of pairs.  Keys are looked up in the association list by linearly scanning the list, which makes association lists inefficient for large numbers of entries.
Arc's <a href="table.html">tables</a> are an alternative to association lists.  Some <a href="http://ycombinator.com/arc/tut.txt">advantages</a> of association lists are that they can preserve order and preserve old values.  Also, multiple association lists can share the same tail.
<p>
For more information on association lists, see <a href="http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node153.html">Common Lisp the Language</a>.  Unlike Common Lisp association lists that are built out of dotted pairs, Arc association lists are built out of list pairs.
<p>
Arc includes functions for looking up keys in an association list, but no explicit support for building association lists.  The lists, however, are simple to create and extend:
<pre class="repl">
arc> (= al '((key1 val1) (key2 val2)))
((key1 val1) (key2 val2))
arc> (push '(key3 val3) al)
((key3 val3) (key1 val1) (key2 val2))
arc> (alref al 'key1)
val1
</pre>