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From: tg1e+@andrew.cmu.edu (Timothy R. Gottschalk)
Newsgroups: comp.lang.prolog
Subject: Prolog Prog. Technique Question
Message-ID: <kalQPim00WB242VkMS@andrew.cmu.edu>
Date: 12 Aug 90 21:15:26 GMT
Organization: Carnegie Mellon, Pittsburgh, PA
Lines: 22

I took a course that introduced Prolog syntax, but never touched prog.
techniques.  Thus, I am feeling my way through.  I am writing code similiar
to the following structure (in Turbo Prolog V2.0):

  loop(In):-
      check_mouse,
      do_eval(In, Out),
      loop(Out).
  loop(_):-
      do_exit.

The compiler recognizes that it is tail-recursive, but still allocates memory
off the heap during each iteration.  As the loop should only be run when
the mouse button is pressed, the check_mouse succeeds when the button is
pressed, but fails otherwise.  Commenting out the check_mouse or do_eval
call does not necessarily stop the heap allocation, although commenting
out both certainly does (of course).  The easiest solution would be to
make a predicate fail somewhere, but, then, how would I be able to get a
return value?  (Using reference vars or internal dbases seems to make the
program run unacceptably slow).

Tim G.