[Haskell-cafe] Re: Ambiguous type with PolymorphicComponents

Maurí­cio briqueabraque at yahoo.com
Sat Mar 7 15:48:25 EST 2009

 >> (...)

> When you have 
> data Test = Test (forall w. (C1 w, C2 w, ..., Cn w) => w)
> and
> function (Test w) = classmethod w,
> there is no way to decide which instance to use, hence the type variable is 
> ambiguous.
> (...)

But, then, how can I reach the data inside a
polymorphic component? Or, better, what can I
do with it? If I say:

function (Test w) = classmethod (w :: specificType)

then I have to suppose that w is always of
'specificType', and this may not be true.


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