How to expand terms and goals in a file for testing term_expansion/2 and goal_expansion/2?

[bakaq]

I'm starting to use term_expansion/2 and goal_expansion/2 more, but they seem quite hard to debug. It would be useful to have a predicate or program that makes all the expansions so that it's easier to debug, similar to something like cargo expand in Rust. Is there already something like this in Scryer?

[triska]

For goal_expansion/2, you can define:

user:goal_expansion(Goal0, Goal) :-
        your_goal_expansion(Goal0, Goal).

In this way, you can use your_goal_expansion/2 manually on the toplevel, to see the expansion of a given goal.

For term_expansion/2, you can do something analogous: Start with a relation your_term_expansion/2 that relates a term to its expansion.

[bakaq]

This is a good start to debug those expansions, but I wanted something more like cargo-expand, turning a file with macros into a file of pure Prolog so that I can more easily see how the whole thing works after expansion. I think it's easier to implement a program like that with this scheme you proposed, but having something more general would be interesting I think.

[triska]

You can implement this with Prolog: Read the terms in the file with read_term/2, expand them, and portray them into another file with portray_clause/2.

[mthom]

expand_term/2 and expand_goal/3 are the public interface to term and goal expansion. The second argument of expand_goal is used to specify the module hosting the goal_expansion predicate.