From: Gilles Dubochet <dubochet@urbanet.ch>
To: caml-list@yquem.inria.fr
Subject: Polymorphic variant typing
Date: Tue, 15 Feb 2005 21:28:52 +0000 [thread overview]
Message-ID: <7bf1f3b95c18eeda0ed169eb7f73d6f0@urbanet.ch> (raw)
Hello everyone,
The following O'Caml expression:
let incr g x = match x with
| `Int i -> `Int (i+1)
| x -> (g x);;
Receives type:
(([> `Int of int ] as 'a) -> ([> `Int of int ] as 'b)) -> 'a -> 'b
Why? I am quite astonished. I would have expected a type more like:
([> ] -> [> ]) -> [> `Int of int ] -> [> `Int of int ]
or in Wand or Rémy-like row variable notation with which I am a little
more comfortable (I am not exactly sure the preceding type is correct
in the 'at leat - at most' notation of O'Caml):
([ 'a ] -> [ 'b ]) -> [ `Int of int | 'a ] -> [ `Int of int | 'b ]
Could anyone be kind enough to give me some clues about where to look
at to find an explanation or even better, explain me what is going on?
I am particularly puzzled by the fact that the g function's *argument*
type is 'at least `Int of int'. This rejects the following code which
seems intuitively correct:
incr (function `Float f -> `Float (f+.1.));;
Thank you.
Cheers,
Gilles.
next reply other threads:[~2005-02-15 21:29 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-02-15 21:28 Gilles Dubochet [this message]
2005-02-15 22:21 ` [Caml-list] " Olivier Pérès
2005-02-15 23:15 ` Gilles Dubochet
2005-02-16 0:36 ` Jacques Garrigue
2005-02-16 1:21 ` Gilles Dubochet
2005-02-16 6:40 ` Jacques Garrigue
2005-02-16 10:12 ` Radu Grigore
2005-02-16 0:43 ` David Brown
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