[wg-camlp4] [Caml-list] Working Group: the future of syntax extensions in OCaml, after camlp4

[Hongbo Zhang]

On 1/29/13 2:44 AM, Alain Frisch wrote:
>
> Let me throw a crazy idea: maybe we could merge the grammar for 
> patterns and expressions, and let the type checker reject bad patterns 
> and bad expressions from this more admissible class. This would give 
> plenty of space for extensions.
>
This is not a crazy idea, it's a beautiful idea, In Fan, we make expr 
and patt symmetric, and defined a new type
expr_patt which is a subtype of both expr and patt(thanks to polymorphic 
variants), it seems that the  Ast lifting only need expr_patt, so the 
part [meta_expr] and [meta_patt] can be shared, which gives much more 
precise type information than the normal sum types, it's so beautiful, XD
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