DCG question: bind to inputs.

[emacstheviking]

Hi,

After reading the manual (section 7.17.1 again) I am still confused... If I have this DCG rule:

foo(X) --> bar(X)

I know it expands to:

foo(X,A,B) :- bar(X, A, B).

How do I add a format statement like this:

foo(X) --> bar(X), {format("bar(X) ok, X is ~w~n", [???])}.

How do I bind to those two input arguments that are the source list and the resulting output list so I can do things with them / to them ? Sure I can print out X because that is in scope as it were but how to get A and B ?? I know this is a simple question and even worse I know I think I already know the answer, I just don't know I know yet.

Thanks,

Sean.