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Message-Id: <20091007.013110.71115501.garrigue@math.nagoya-u.ac.jp>
To: rich@annexia.org
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Constructors are not functions
From: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
In-Reply-To: <20091006152404.GA19326@annexia.org>
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X-Spam: no; 0.00; constructors:01 camlp:01 ocaml:01 syntax:01 typable:01 transforming:01 dumped:01 caml-list:01 functions:01 expression:02 garrigue:03 garrigue:03 theoretical:03 strong:96 jacques:03 

From: Richard Jones <rich@annexia.org>
> It would be so nice to have a macro tool which was aware of types, but
> that tool isn't camlp4.  There are probably theoretical problems with
> this, but having a "give_me_the_type_of (ocaml_subexpression)"
> function would be awesome indeed.

The trouble here is that the type of the subexpression depends on its
context... so that you would need to have already typed the whole
expression to do that. If you are extending the syntax, this is a
rather strong requirement. On the other hand, if you design your
extension so that the program is typable before transforming it, then
it would not be theoretically impossible to have campl4 read the
dumped types and use them for an extra pass. You would still need to
type everything once more after that for safety.

Jacques Garrigue