From: Keith Wansbrough <Keith.Wansbrough@cl.cam.ac.uk>
To: Jon Harrop <jon@jdh30.plus.com>
Cc: caml-list <caml-list@inria.fr>
Subject: Re: [Caml-list] Factoring HOFs [was Re: C++ STL...]
Date: Thu, 30 Sep 2004 11:13:00 +0100 [thread overview]
Message-ID: <E1CCxvo-0007By-00@mta1.cl.cam.ac.uk> (raw)
In-Reply-To: Your message of "Wed, 29 Sep 2004 17:49:17 BST." <200409291749.17226.jon@jdh30.plus.com>
> Yipes! Ok, so I'm missing some typing subtlety. Why does this end up with a
> single polymorphic type:
>
> # let map_2 m g f x = m g (m f x);;
> val map_2 : ('a -> 'b -> 'b) -> 'a -> 'a -> 'b -> 'b = <fun>
You want it to have type
(forall 'a 'b 'f. ('a -> 'b) -> ('a 'f -> 'b 'f))
-> ('b -> 'c)
-> ('a -> 'b)
-> 'a 'f
-> 'b 'f
but OCaml doesn't allow nested quantifiers (i.e., higher-rank
polymorphism).
It actually wouldn't be very hard to support, if you're prepared to
accept the need for the occasional type annotation - see
http://research.microsoft.com/~simonpj/papers/putting/index.htm.
--KW 8-)
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next prev parent reply other threads:[~2004-09-30 10:13 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-25 21:12 [Caml-list] C++ STL and template features compared with OCaml parametric polymorphism and OO features Vasili Galchin
2004-09-25 21:38 ` Nicolas Cannasse
2004-09-25 22:15 ` Vasili Galchin
2004-09-25 22:52 ` Vasili Galchin
2004-09-26 1:34 ` Jon Harrop
2004-09-26 5:31 ` Radu Grigore
2004-09-26 9:47 ` sejourne_kevin
2004-09-26 13:05 ` Jon Harrop
2004-09-26 14:36 ` skaller
2004-09-26 15:08 ` sejourne_kevin
2004-09-26 15:27 ` skaller
2004-09-26 18:51 ` Jon Harrop
2004-09-26 20:14 ` Radu Grigore
2004-09-27 1:59 ` Jon Harrop
2004-09-27 4:48 ` skaller
2004-09-27 9:40 ` Jacques GARRIGUE
2004-09-27 10:50 ` Radu Grigore
2004-09-27 12:14 ` skaller
2004-09-27 13:11 ` Jon Harrop
2004-09-27 13:31 ` Radu Grigore
2004-09-27 16:54 ` Jon Harrop
2004-09-29 18:59 ` Radu Grigore
2004-09-27 13:32 ` Radu Grigore
2004-09-27 14:04 ` Brian Hurt
2004-09-27 14:58 ` skaller
2004-09-27 15:30 ` Brian Hurt
2004-09-27 16:38 ` skaller
2004-09-27 17:01 ` Brian Hurt
2004-09-28 1:21 ` skaller
2004-09-27 16:41 ` brogoff
2004-09-28 0:26 ` skaller
2004-09-29 15:32 ` Florian Hars
2004-09-29 16:49 ` [Caml-list] Factoring HOFs [was Re: C++ STL...] Jon Harrop
2004-09-30 9:19 ` Radu Grigore
2004-09-30 10:13 ` Keith Wansbrough [this message]
2004-09-30 10:31 ` Keith Wansbrough
2004-09-30 13:21 ` skaller
2004-09-30 23:17 ` [Caml-list] Factoring HOFs Jacques Garrigue
2004-10-01 8:46 ` Keith Wansbrough
2004-10-01 17:35 ` brogoff
2004-09-26 20:43 ` [Caml-list] C++ STL and template features compared with OCaml parametric polymorphism and OO features skaller
2004-09-26 14:19 ` skaller
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