🚀 go-pugleaf

In article <9671@lll-winken.llnl.gov> daven@lll-crg.llnl.gov (Dave Nelson) writes:
>Could someone tell me why prolog has no built-in macro facility?
>Even the industrial strength, full-featured prolog I am currently
>evaluating doesn't have such a thing.
>
>daven (Dave Nelson)
>

I did some experiements with this kind of thing with a parser and found that 
it slowed the program down.  I think that this is because current Prolog compilers
dont handle very large clauses well.  Consider this example:

p(X):-
    q(X),
    r(X),
    s(Y).

q(tree(_,_,_,_)).


If we turn q into a macro, then the resulting clause for p is:

p(tree(A,B,C,D)):-
    r(tree(A,B,C,D)),
    s(tree(A,B,C,D)).


Note also that where there use to be a single variable X that pointed to the
structure tree/4, now there isnt.

In my application, the use of macros made the size of the resulting clauses enormous.
The resulting program ran as much as 2 times slower than the version with
procedure calls.

John Dowding

dowding@prc.unisys.com