export in syntax-rules

export in syntax-rules

[Kevin Ryde]

In guile 1.6.1 on a recent i386 debian, I thought to use "export"
inside a syntax-rules in a module definition, for instance

    (define-module (abc def)
      #:use-module (ice-9 syncase))

    (define-syntax foo
      (syntax-rules ()
        ((foo name)
         (export name))))

    (define x 123)
    (foo x)

But I got an error,

    ERROR: In procedure variable-ref:
    ERROR: Wrong type argument in position 1 (expecting variable): #f

Is this sort of thing meant to work, or have I made some basic error?

(I was looking to make "-public" versions of some macros.  I got the
effect I wanted with a procedure->macro, but just wondered if the
syntax-rules style was valid.)


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Re: export in syntax-rules

[Mikael Djurfeldt]

Kevin Ryde <user42@zip.com.au> writes:

> In guile 1.6.1 on a recent i386 debian, I thought to use "export"
> inside a syntax-rules in a module definition, for instance
>
>     (define-module (abc def)
>       #:use-module (ice-9 syncase))

You might want to use #:use-syntax (ice-9 syncase) here instead,
otherwise syntax-case expansion is only invoked when syntax-case
macros are called in an s-expression.  That disables singleton macros
and can cause unexpected errors with regard to scope.

>     (define-syntax foo
>       (syntax-rules ()
>         ((foo name)
>          (export name))))
>
>     (define x 123)
>     (foo x)
>
> But I got an error,
>
>     ERROR: In procedure variable-ref:
>     ERROR: Wrong type argument in position 1 (expecting variable): #f
>
> Is this sort of thing meant to work, or have I made some basic error?
>
> (I was looking to make "-public" versions of some macros.  I got the
> effect I wanted with a procedure->macro, but just wondered if the
> syntax-rules style was valid.)

This is caused by a bug in syncase.scm.  I've fixed this in CVS 1.7.0
and in the 1.6 branch.  1.6.2 will contain the fix.

2003-01-27  Mikael Djurfeldt  <djurfeldt@nada.kth.se>

	* syncase.scm (guile-macro): Strip syntactic information from
	expression before trying to treat it as a Guile macro call.
	(Thanks to Kevin Ryde.)


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Re: export in syntax-rules

[Kevin Ryde]

Mikael Djurfeldt <djurfeldt@nada.kth.se> writes:
>
> You might want to use #:use-syntax (ice-9 syncase) here instead,
> otherwise syntax-case expansion is only invoked when syntax-case
> macros are called in an s-expression.  That disables singleton macros
> and can cause unexpected errors with regard to scope.

Oh, I see, say "(display foo)" gets foo expanded (as invalid I guess)
under use-syntax, but not under use-modules.

Tricky stuff.  I put use-module without really paying attention to the
doco, and it worked, so I thought no more of it :-).


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