Re: [Guile-commits] GNU Guile branch, syncase-in-boot-9, updated. e3c5df539640a36eb1493f581087d54a4714f337

[Andy Wingo]

Hi,

On Wed 03 Jun 2009 00:35, Neil Jerram <address@hidden> writes:

> Andy Wingo <address@hidden> writes:
>
>>>>     * module/ice-9/boot-9.scm: Remove #' read-hash extension, which 
>>>> actually
>>>>       didn't do anything at all. It's been there since 1997, but no Guile
>>>>       code I've ever seen uses it, and it conflicts with #'x => (syntax x)
>>>>       from modern Scheme.
>>>
>>> I find this point questionable.  Do we really need to break this
>>> functionality?  It would be nicer if we could both keep
>>> `read-hash-extend' and the functionality you want.  What do you think?
>>
>> `read-hash-extend' is still there. This just removed the #'
>> read-hash-extension, which was the identity extension: #'foo == foo.
>>
>> `read-hash-extend' overrides any core hash forms, so this extension
>> prevented #'foo == (syntax foo). It would be easy for an affected reader
>> to add this particular extension back, though.
>
> I don't think we need to worry much about preserving the #' read-hash
> extension, however:
>
> (1) Doesn't #'x => (syntax x) need to apply only in the lexical RHS of
> a syntax-case syntax transformer?  Perhaps then we could implement
> this meaning of #'x only in this limited scope, and retain the older
> meaning in other scopes?

Yes, although you can't determine that before macroexpansion, so it's
akin to `unquote' outside of `quasiquote'.

> (2) We should of course mention the removal of the old #' in NEWS, and
> as part of that entry it would be good to say in detail how "It would
> be easy for an affected reader to add this particular extension
> back".  (Which I assume just means providing the necessary
> (read-hash-extend ...) incantation.)

Yes. I'll get on the NEWS this weekend.

Cheers,

Andy
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