There are several interesting problems with co-routing. For example we want to reclaim unreached frozen goals. But there is a problem for Prolog systems that don't support cyclic terms. Namely a freeze:
?- freeze(V, p(...V...)).
leads to a loop in the internal data structure. A simple workaround would be currying the frozen goal. Thus instead of working with a predicate freeze/2, we would work with a predicate guard/2, which could be defined as follows:
guard(V, C) :- freeze(V, call(C, V)).
But how could we define freeze/2 in terms of guard/2? The obvious definition doesn't work, since it doesn't introduce a new variable, and we still have the problem that the closure contains V (assuming a lambda library where (\)/2 is the lambda abstraction):
freeze(V, G) :- guard(V, V\G).
Bye
