RE: [Sml-implementers] Structure sharing and type abbreviations

[Robert H. <Rob...@cs...>]

I support adding "where structure", since it is clearly necessary in
practice.  Adding "withtype" to signatures seems entirely reasonable as
well, provided that we can agree on the semantics of signature matching in
their presence.

More generally, I would like to open discussion about more extensive changes
and extensions to Standard ML.  What do the readers on this list think
should be done next in the evolution of the language?

Bob Harper

-----Original Message-----
From: Andreas Rossberg [mailto:ros...@ps...]
Sent: Friday, September 14, 2001 10:18 AM
Cc: sml...@li...
Subject: Re: [Sml-implementers] Structure sharing and type abbreviations


Dave Berry wrote:
> 
> Should we also consider supporting "where structure..."? And perhaps
> removing the "and" derived form of "where type...", which I believe is
> ambiguous.

It is not ambiguous, only tedious to parse. As it stands this part of
the grammar is LALR(2) but a bunch of ugly transformations can turn it
into LALR(1). Of course, it is pretty useless anyway.

Regarding "where" for structures: I second it would be great if all
implementations supported it (together with a derived form for
definitional structure specifications) since that would allow getting
rid of sharing constraints in programs altogether. IMHO this would be
preferable to relying on a relaxed structure sharing semantics.

Still I think adopting the proposal is a good idea. I would also opt for
variation 2 since I do not see any application for such obfuscated uses
of sharing (but maybe I'm just not imaginative enough...)

BTW, another old issue that definitely ought to be fixed by all
implementations: allow the "datatype ... withtype" derived form in
signatures...

	- Andreas

-- 
Andreas Rossberg, ros...@ps...

"Computer games don't affect kids; I mean if Pac Man affected us
 as kids, we would all be running around in darkened rooms, munching
 magic pills, and listening to repetitive electronic music."
 - Kristian Wilson, Nintendo Inc.

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