On Sun, 6 Apr 2008, Thomas M. DuBuisson wrote:
Id is an operation over types yielding a type, as such it doesn't make
much sense to me to have (Id a -> Id a) but rather something like (a ->
Id a). One could make this compile by adding the obvious instance:
type instance Id a = a
Curiously, is this a reduction from a real world use of families? I
just can't think of how a (Fam a -> Fam a) function would be of use.
Yes, it's cut down from an example where (I think) I really need the type
signature to specialise a general function that does do something useful.
The generalised intstance above wouldn't be valid or sensible in that
context.
Cheers,
Ganesh
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