🚀 go-pugleaf

In IBM-Prolog, I wouldn't dream of using assert/retract; instead,
I would use the internal database (similar to record, but better):

	term_get(name, Value) &
	term_assert(name, ? Value + 1)	% "?" triggers functional evaluation

It's actually quite efficient (maybe it shouldn't be so efficient;
we don't really want to encourage this kind of thing).  
As a variant, if I do:

	term_get(name, Value) &
	term_put(name, ? Value + 1)

the change is undone on backtracking (or when the query has no more solutions).

Not only that, but I could tell the system that term_get_f(name) is a
functional abbreviation for term_get(name,Value) and do this:

	term_put(name, ? term_get_f(name) + 1)

By the way, IBM-Prolog allows multiple keys.  As an example, all the
pragma and scanner values are kept in this internal data base.  So,
to change the scanner to accept [a!b] instead of [a|b] (for example, on 
a Japanese keyboard which is missing the bar character), I just enter:

	<- term_assert(assignable,6,"!") .	% 6 is the cons char's index

In fact, that's how IBM-Prolog implements Edinburgh syntax: there's
a built-in predicate which just does a series of such term_assert()s.

- peter ludemann	pgl@cup.portal.com