Expanding macros

Expanding macros

[Panicz Maciej Godek]

Hey,
is there any legitimate way to expand the scheme macros
to the scheme code in guile 2.0?
The macroexpand procedure seems only to compile the code
to the tree-il language (no matter whether 'e, 'c or any other
symbol is passed as a second argument):

(macroexpand '(define (f a b) (list a b)) 'e)
; ===> #<tree-il (define f (lambda ((name . f)) (lambda-case (((a b)
#f #f #f () (a-4236 b-4237)) (apply (toplevel list) (lexical a a-4236)
(lexical b b-4237))))))

thanks
MG

Re: Expanding macros

[Ludovic Courtès]

Hi,

Panicz Maciej Godek <godek.maciek@gmail.com> skribis:

> is there any legitimate way to expand the scheme macros
> to the scheme code in guile 2.0?
> The macroexpand procedure seems only to compile the code
> to the tree-il language (no matter whether 'e, 'c or any other
> symbol is passed as a second argument):
>
> (macroexpand '(define (f a b) (list a b)) 'e)
> ; ===> #<tree-il (define f (lambda ((name . f)) (lambda-case (((a b)
> #f #f #f () (a-4236 b-4237)) (apply (toplevel list) (lexical a a-4236)
> (lexical b b-4237))))))

There’s the ,expand command at the REPL.

It’s implemented like this:

  (define (repl-expand repl form)
    (let ((from (repl-language repl))
          (opts (repl-compile-options repl)))
      (decompile (compile form #:from from #:to 'tree-il #:opts opts
                          #:env (current-module))
                 #:from 'tree-il #:to from)))

Psyntax, the macro expander, returns tree-il, hence the need to go
through ‘decompile’.

Thanks,
Ludo’.

Re: Expanding macros

[Panicz Maciej Godek]

Bonjour,

> There’s the ,expand command at the REPL.
>
> It’s implemented like this:
>
>   (define (repl-expand repl form)
>     (let ((from (repl-language repl))
>           (opts (repl-compile-options repl)))
>       (decompile (compile form #:from from #:to 'tree-il #:opts opts
>                           #:env (current-module))
>                  #:from 'tree-il #:to from)))
>
> Psyntax, the macro expander, returns tree-il, hence the need to go
> through ‘decompile’.

Thanks a lot. By the way, the (undocumented, as of 2.0.5) decompile
function returns two values -- the first being the expanded expression
and the second -- #f.
As I've figured out from system/base/compile, the second return value
is the environment, but I've been wondering under what circumstances
would that value be different from #f.

Best regards
MG

Re: Expanding macros

[Ludovic Courtès]

Hi,

Panicz Maciej Godek <godek.maciek@gmail.com> skribis:

> By the way, the (undocumented, as of 2.0.5) decompile
> function returns two values -- the first being the expanded expression
> and the second -- #f.
> As I've figured out from system/base/compile, the second return value
> is the environment, but I've been wondering under what circumstances
> would that value be different from #f.

AFAICS it’s currently unused.

Thanks,
Ludo’.