From: John Max Skaller <skaller@ozemail.com.au>
To: Mattias Waldau <mattias.waldau@abc.se>
Cc: Caml-List <caml-list@inria.fr>
Subject: Re: Same label in different types, how do people solve this?
Date: Fri, 08 Dec 2000 03:49:17 +1100 [thread overview]
Message-ID: <3A2FBF8D.997AFE7@ozemail.com.au> (raw)
In-Reply-To: <HDEEKOMJILGEIHIMAPCDMEJMDLAA.mattias.waldau@abc.se>
Mattias Waldau wrote:
>
> In Ocaml, you cannot have the same label in different types, see the example
> below where
> point_2d hides point_3d.
>
> How do people normally code around this restriction?
Use distinct names :-)
The 'correct' solution is a bit messy: use modules.
> Also, I am a bit curious why it doesn't help to type explicitely, i.e. to
> write
> let x:point_3d={x=10.;y=20.;z=30.} ???
The RHS is typed without examining the type constraint on the LHS,
then the constraint is checked. As in:
let f (x : int) : int = "Hello"
The type of f is first infered as 'a -> string, as if it had been
written
let f x = "Hello"
then this type is unified with the declared type constraint. In your
example,
the type is infered to be point_2d, since you declared that second, and
the
field name 'x' is associated with this type: the previous binding
of x to (a field of the) type point_2d is hidden.
For your example try:
module D3 = struct
type point = {
x:float;
y:float;
z:float;
}
end
module D2 = struct
type point = {
x:float;
y:float;
}
end
;;
{D3.x=10.;D3.y=20.;D3.z=30.};;
The 'field names' escape out of the type like a C enumeration,
to allow type inference to deduce the type of a record literal.
--
John (Max) Skaller, mailto:skaller@maxtal.com.au
10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
checkout Vyper http://Vyper.sourceforge.net
download Interscript http://Interscript.sourceforge.net
next prev parent reply other threads:[~2000-12-08 9:04 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-12-06 21:22 Mattias Waldau
2000-12-07 16:49 ` John Max Skaller [this message]
2000-12-07 18:34 ` Maxence Guesdon
2000-12-07 23:02 ` Gerd Stolpmann
2000-12-08 1:22 ` Jacques Garrigue
2000-12-08 9:31 ` Sven LUTHER
2000-12-08 9:36 ` Pierre Weis
2000-12-08 9:48 ` Sven LUTHER
2000-12-08 18:41 ` John Max Skaller
2000-12-08 9:40 ` Nicolas barnier
2000-12-08 16:36 ` Brian Rogoff
2000-12-11 17:19 ` Pierre Weis
2000-12-10 12:49 ` Mattias Waldau
2000-12-11 18:23 ` Chris Hecker
2000-12-11 19:17 ` Pierre Weis
2000-12-12 10:02 ` Sven LUTHER
2000-12-12 3:25 ` Chet Murthy
2000-12-12 17:43 ` John Max Skaller
2000-12-12 19:24 ` Functions must be explicitly typed, (was Same label in different types, how do people solve this?) Mattias Waldau
2000-12-13 0:51 ` John Max Skaller
2000-12-15 10:13 ` Andreas Rossberg
2000-12-15 12:50 ` Frank Atanassow
2000-12-14 18:42 ` Stefan Monnier
2000-12-15 12:47 ` Pierre Weis
2000-12-15 13:39 ` Mattias Waldau
2000-12-15 23:37 ` Brian Rogoff
2000-12-16 14:10 ` ROverloading John Max Skaller
2000-12-15 21:51 ` Same label in different types, how do people solve this? Bruce Hoult
2000-12-12 17:19 ` John Max Skaller
2000-12-10 14:57 Ohad Rodeh
2000-12-13 13:17 Dave Berry
2000-12-13 14:31 ` Mattias Waldau
2000-12-15 10:01 ` John Max Skaller
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