From: Richard Jones <rich@annexia.org>
To: caml-list@inria.fr
Subject: [Caml-list] Fwd: Polymorphic optional label argument, with default
Date: Sat, 10 Apr 2004 22:36:16 +0100 [thread overview]
Message-ID: <20040410213616.GA28863@redhat.com> (raw)
Hi:
I posted the message below originally on ocaml_beginners. There were
many helpful responses, and the general consensus was that this was
not possible, but no one could give a definitive answer. I just
wanted to confirm on the 'grown-ups' list (:-) if this is really true
before I finalise the API I am designing.
Thanks,
Rich.
To: ocaml_beginners@yahoogroups.com
From: Richard Jones <rich@annexia.org>
Subject: Polymorphic optional label argument, with default
I have a function defined:
let plot ?(labels = string_of_int) graph =
(* ... *)
The idea of the optional 'labels' argument is to specify a polymorphic
function 'a -> string which is used to print labels stored in the
'graph' argument.
The problem is that because string_of_int is obviously int -> string,
my function is typed as:
plot : ?labels : (int -> string) -> (* ... int ... *) -> unit
but I want it to be typed as:
plot : ?labels : ('a -> string) -> (* ... 'a ... *) -> unit
[The 'a types are the same type. If I leave out the initializer, then
it works.]
How to?
Rich.
--
Richard Jones. http://www.annexia.org/ http://www.j-london.com/
Merjis Ltd. http://www.merjis.com/ - improving website return on investment
Perl4Caml lets you use any Perl library in your type-safe Objective
CAML programs. http://www.merjis.com/developers/perl4caml/
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next reply other threads:[~2004-04-10 21:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-04-10 21:36 Richard Jones [this message]
2004-04-10 22:40 ` Gerd Stolpmann
2004-04-11 0:03 ` skaller
2004-04-10 23:52 ` Matt Gushee
2004-04-11 6:26 ` Brian Hurt
2004-04-11 8:33 ` Richard Jones
2004-04-11 9:01 ` skaller
2004-04-11 13:16 ` Jacques Garrigue
2004-04-11 15:23 ` nadji
2004-04-12 2:25 ` Jacques Garrigue
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