A.6.2.3 Example

(defun palindromep (x)

  (with-prolog

    (append ?a (?b . ?c) ?.x) ; note "?.x" reference

    (or (reverse ?a ?c)

        (reverse ?a (?b . ?c)))))

(palindromep '(yes no maybe))

returns:

NIL (palindromep '(yes no maybe no yes))

returns:

T

The body of a with-prolog returns t if it succeeds and a non-local exit is not executed. It returns nil on failure.

LispWorks KnowledgeWorks and Prolog User Guide - 14 Dec 2001