expanding define-syntax

[svenha]

Is there a way in Gerbil to expand a source file to another file so that all macro uses (define-syntax would be enough for the moment) are expanded? (Like alexpander does, but without the artifacts that alexpander introduces.)

[vyzo]

You still want it in Gerbil source? There is no easy way to save the expanded output of the compilation process, best we have is expanding to Gambit source.

[vyzo]

You can easily get the expanded source however from the module context -- module-context-code, which you could write to a file.

[vyzo]

So to recap: import your source file directoy with import-module and then use module-context-code in the resulting module context object to get the code, which you can then write to a file.

[svenha]

You still want it in Gerbil source?

Little more complicated. The input and the output should be some Scheme dialect as defined by implementations like Chicken or Bigloo.

import-module

Thanks! This works if the source is Gerbil-compatible. For other Scheme dialects, I get such errors for identifiers not defined in Gerbil:

Syntax Error: Reference to unbound identifier

I cannot define these identifiers because the input file to be macro-expanded is for other Scheme dialects. Can these errors be relaxed to warnings? Or any other ideas?

[vyzo]

You need to somehow define these identifiers, perhaps with an extern. You can have a custom prelude for each dialect, which provides the necessary symbols.

[svenha]

So to recap: import your source file directly with import-module and then use module-context-code in the resulting module context object to get the code, which you can then write to a file.

What does module-context-code return? https://cons.io/reference/core-expander.html#module-context-code is empty. How do I get the s-expressions?

[vyzo]

Yeah, the documentation is not there for the expander yet. It returns a syntax object containing the source code that was expanded. You can process the syntax object with the regular expander facilities (syntax-case, stx-* procedures, etc). You can import the expander runtime (<expander-runtime>) or the expander itself (:gerbil/expander) to get them in scope. If you want to turn it into a datum, say for pretty printing, then (syntax->datum code) will do.

[vyzo]

If you need syntax-case at runtime, you can import <syntax-case>.

[svenha]

Thanks, that worked for me. But I must say that the source is already transformed quite a lot. OK, now I know how it looks like :-) and it definitely helps in certain situations.