sc-expand on syntax-case form

sc-expand on syntax-case form

[Julian Graham]

Hi Guilers,

Is sc-expand in `(ice-9 syncase)' supposed to be able to expand the
syntax-case form?  When I try to run it on an expression that includes
a syntax-case form that looks like:

  (syntax-case foo () ... )

...I get "invalid syntax ()", presumably because () isn't valid Scheme
syntax outside of some well-known special forms -- does this style of
syntax-case need to be added to sc-expand's list of acceptable syntax?
 PLT's version of the syntax-case expander (`expand') doesn't seem to
have any trouble with this.  For what it's worth, in Guile:

  (sc-expand '(lambda () (quote ())))

produces

  (lambda () (quote ()))

...while

  (sc-expand '(let () (quote ())))

produces

  (quote ())

That last one strikes me as a little weird.


Regards,
Julian

Re: sc-expand on syntax-case form

[Julian Graham]

Okay, I think I've (tentatively) figured this one out:

Instead of `sc-expand', the proper function to use is `syncase'.  (And
you can use `save-module-excursion' if expansion needs to happen with
regard to a particular module environment.)


On Sun, Feb 22, 2009 at 8:13 PM, Julian Graham <joolean@gmail.com> wrote:
> Hi Guilers,
>
> Is sc-expand in `(ice-9 syncase)' supposed to be able to expand the
> syntax-case form?  When I try to run it on an expression that includes
> a syntax-case form that looks like:
>
>  (syntax-case foo () ... )
>
> ...I get "invalid syntax ()", presumably because () isn't valid Scheme
> syntax outside of some well-known special forms -- does this style of
> syntax-case need to be added to sc-expand's list of acceptable syntax?
>  PLT's version of the syntax-case expander (`expand') doesn't seem to
> have any trouble with this.  For what it's worth, in Guile:
>
>  (sc-expand '(lambda () (quote ())))
>
> produces
>
>  (lambda () (quote ()))
>
> ...while
>
>  (sc-expand '(let () (quote ())))
>
> produces
>
>  (quote ())
>
> That last one strikes me as a little weird.

Re: sc-expand on syntax-case form

[Neil Jerram]

Julian Graham <joolean@gmail.com> writes:

> Okay, I think I've (tentatively) figured this one out:
>
> Instead of `sc-expand', the proper function to use is `syncase'.  (And
> you can use `save-module-excursion' if expansion needs to happen with
> regard to a particular module environment.)

Hi Julian,

Just to comment a bit, although I really don't understand syncase
well...

Using `syncase' rather than `sc-expand' sounds right to me.  Guile's
`use-syntax' hack requires the transformer producer to have the same
name as the module that defines it, so it's expected that `syncase' is
the top-level transformer.

Regards,
        Neil