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Re: syntax-local-value patch for discussion

From: Ian Price
Subject: Re: syntax-local-value patch for discussion
Date: Thu, 08 Dec 2011 21:58:01 +0000
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux)

Stefan Israelsson Tampe <address@hidden> writes:

> So I tried to get hold of the macro binding. So with the following patch wich 
> should be enogh
> for me to make progress porting rackets syntax parse to guile.
> Would be very glad if we could find a interface to expose this information 
> that is sane
> and rigid manner. So we should discuss this feature.
As it stands, I agree it is pretty simplistic, but I'm not sure what to
propose :) What is the intended use cases for this? A compile-time
values mechanism?

> Anyway about the patch.
> I added a fluid that is setted with a closure that captures enough syntax 
> information
> so that we can lookup the macro value local or global. It basically uses the 
> same method
> as psyntax macroexpander.
The patch looks fine to me, although I admit I have little experience
with psyntax.

> Now we can write,
> (define-syntax info
>   (lambda (x)
>     (syntax-case x ()
>       ((_ x)
>         (pk (syntax-binding-info (syntax->datum #'x)))
>         #'#f))))
FWIW, I wouldn't expect to have to pass a raw datum to any procedure
with a syntax prefix. If we keep this procedure, I think the
syntax->datum should be hid, or the procedure renamed.

> So with this I can attach meta information to macros local or not by
> using a weak hash.
I have 'define-type' & 'type-case' macros, basically copied from
racket's plai language[0][1] , that suffers from a complete lack of
error handling in the case where the type-id is not, in fact, a
type-id. If I were to use this mechanism, I would create a weak hash of
datatype-ids, adding them to the hash with 'define-type', and checking
if they are in the hash in my 'type-case' macro. Would that be right?

1. I can post these if people want them
Ian Price

"Programming is like pinball. The reward for doing it well is
the opportunity to do it again" - from "The Wizardy Compiled"

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