We’ve skipped over a fair number of functions that, while maybe not commonly used, are fairly simple in their use and descriptions.  We’ll discuss pairlis a bit, simply because association lists are useful, but their manipulations aren’t always completely covered.  You’ll recall I began this alphabetical series of Lisp features with acons, and now we’ll talk about pairlis.

With acons, the programmer can add a new key/value pair to an association list.  The pairlis function extends this to a list of keys and a list of corresponding values.

In the acons example, I built up an association list as follows:
 

CL-USER> (let (alist)
           (setf alist (acons 1 "ONE" alist))
           (setf alist (acons 2 "TWO" alist))
           (setf alist (acons 3 "THREE" alist))
           alist)
((3 . "THREE") (2 . "TWO") (1 . "ONE"))

Here’s how you can do this more simply with pairlis:
 

CL-USER> (let ((alist (pairlis '(1 2 3) '("ONE" "TWO" "THREE"))))
           alist)
((3 . "THREE") (2 . "TWO") (1 . "ONE"))

Remember this function when you want to build multiple association list entries in code.