Returns an association list that associates
elements of keys to corresponding elements of data.
The consequences are undefined if keys and data are
not of the same length.
If alist is supplied, pairlis returns
a modified alist with the
new pairs prepended to it.
The new pairs may appear in the resulting association list in
either forward or backward order.
The result of
(pairlis '(one two) '(1 2) '((three . 3) (four . 19)))
((one . 1) (two . 2) (three . 3) (four . 19))
((two . 2) (one . 1) (three . 3) (four . 19))