Le 2012-08-14 04:31, Invisible a écrit :
> On 14/08/2012 02:01 AM, Darren New wrote:
>
>> It probably lets you return an opaque reference to
>> something you can't see the type of, but I doubt it lets you return a
>> type that you can't see.
>
>    module Foobar (Foo (..), foobar) where
>
>    data Foo = Foo Int deriving Show
>    data Bar = Bar Int deriving Show
>
>    foobar :: Foo -> Bar
>    foobar (Foo x) = Bar x
>
> Notice how Bar is not exported, yet foobar is exported, and its return
> type is Bar.

Correct me if I'm wrong, but apart from showing that the standard 
seemingly allows it, how would you use that in a real world scenario?

By exporting foobar, you intend to use it somewhere else in your code, 
right? Which means there's another piece of code somewhere that expects 
to receive something of type bar, without knowing what type bar actually is!

How does that work?


-- 
/*Francois Labreque*/#local a=x+y;#local b=x+a;#local c=a+b;#macro P(F//
/*    flabreque    */L)polygon{5,F,F+z,L+z,L,F pigment{rgb 9}}#end union
/*        @        */{P(0,a)P(a,b)P(b,c)P(2*a,2*b)P(2*b,b+c)P(b+c,<2,3>)
/*   gmail.com     */}camera{orthographic location<6,1.25,-6>look_at a }

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