🚀 go-pugleaf

In article <869@gamera.cs.utexas.edu>, bradley@cs.utexas.edu (Bradley L. Richards) writes:
> As far as I'm aware, little work *has* been done in this area

The first paper I saw on the subject was Chris Mellish's paper about
the Prolog component of PopLog.  I've seen several others since (alas,
my library is in two other countries at the moment, so no reference)
and they mostly follow his approach.  Ignoring arguments,

	p :-
		built-in-test.
	p :-
		q.
	p :-
		r, s.

is compiled as a function with a continuation argument:  if it succeeds
it calls its continuation; if it fails it returns.

	define p(Continuation);
	    if built-in-test then
		call(Continuation);
	    endif;
	    q(Continuation);
	    r(lambda (). s(Continuation endlambda);
	    ;; fail by returning
	enddefine;

The top-level predicate is called with a continuation which prints
the variable bindings and then either returns (if the user types ";")
or longjumps all the way out (if the user types <CR>).  I don't
remember how cuts are handled.  In a language like C which doesn't
let you construct closures (lambda ... endlambda) you can get the
same effect by pushing information on a "continuation stack".

There are actually some similarities between this method and David
Warren's "total non-structure-sharing".