From: skaller <skaller@users.sourceforge.net>
To: Jon Harrop <jon@jdh30.plus.com>
Cc: caml-list <caml-list@inria.fr>
Subject: Re: [Caml-list] C++ STL and template features compared with OCaml parametric polymorphism and OO features
Date: 27 Sep 2004 14:48:03 +1000 [thread overview]
Message-ID: <1096260483.28613.426.camel@pelican.wigram> (raw)
In-Reply-To: <200409270259.43863.jon@jdh30.plus.com>
On Mon, 2004-09-27 at 11:59, Jon Harrop wrote:
> In practice, I'm all for
> aggressive factoring but I can't see what we're factoring here...
Sure you can. Consider:
type 'a F = A | B of 'a | C of 'a * 'a * int
Can you write a map function for this? Of course you
can! What about:
type 'a F = A of int | C of 'a * int | X of 'a F * 'a
Yes, of course you can!
Its obvious how to do it!
There *exists* a universal algorithm in your head
for writing map functions. But this pattern cannot
be encoded in Ocaml as an HOF:
map: 'a 'F -> ('a -> 'b) -> 'b 'F
You can do this provided you have only types built
from variants, tuples, and recursion (no function types).
In fact you could probably write this function
in camlp4 from the definition of each type
for which you need a map.
--
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850,
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net
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next prev parent reply other threads:[~2004-09-27 4:48 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-25 21:12 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 [this message]
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
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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