[wg-camlp4] Against the use of syntactically-valid OCaml code for syntax extension purposes

[Alain Frisch]

On 01/30/2013 07:31 AM, Gabriel Scherer wrote:
> My understanding is that this is precisely what type-conv does:
> annotate the type declaration itself, rather than the type expression
> or the whole phrase.

I agree it make sense to allow attaching attributes to various syntactic 
constructions, including those which are not "algebra", and type 
declaration are a good candidate for that.  Note that when I proposed 
attributes, I wrote:

> I propose to start discussing the addition of attributes to most syntactic categories (expressions, type expressions, patterns, type declarations, module expressions, structure/signature items, etc).

I'm not sure we need to allow attributes on specific parts of expression 
kinds (e.g. annotate the "for" itself, or each binding in a "let"). I'm 
not fundamentally opposed to it, but it will add a lot of complexity to 
the Parsetree with no obvious benefit.  This probably needs to be 
discussed on a case-by-case basis.

> Finally, using a
> convention to annotate the pattern may give rise to critical pairs /
> ambiguities where the semantics of the program depends of whether we
> consider the annotation to cover the pattern or the declaration (for
> annotations that make sense in both, eg. @profile).

Yes, but it does not seem difficult to have a different convention for 
something related to the pattern itself and something related to the 
binding, if the same general notion need to apply to both.

Alain