How to implement a time limited execution mechanism in CLISP?

Question

What I have in mind is something like:

(run (long-calculation vars) time-limit)

which returns the result of (long-calculation vars) or nil if time-limit is reached.

Answer 1

If you could find an implementation for the amb operator, then you could do something like this:

(defmacro run (comp time-limit)
  `(amb comp
       (progn (delay ,time-limit)
              nil)))

Be careful not to mistake this with the McCarthy amb operator. amb should evaluate both its arguments in separate threads and pick whichever finishes first. For example, in Haskell, it's described in Data.Unamb.

Answer 2

I would suggest using bordeaux-threads, spawning a thread for the computation, and if it doesn't return by the timer, reaping the thread and returning nil.