OK, thanks for this advice.
The type definition compiles, but when I try to actually access
myField, the compiler says:
Cannot use record selector `myField' as a function due to escaped type
variables
Probable fix: use pattern-matching syntax instead
So I took the hint and wrote a new pattern matching accessor function:
getMyField (MyStruct value) = value
and I get:
Inferred type is less polymorphic than expected
Quantified type variable `a' escapes
When checking an existential match that binds
value :: a
Any further suggestions?
On Sep 26, 1:09 pm, Daniel Fischer <[email protected]> wrote:
> On Sunday 26 September 2010 12:53:46, Michael Snoyman wrote:
>
> > data MyStruct = forall a. MyTypeClass a => MyStruct {myField :: a}
>
> Note that that requires
> {-# LANGUAGE ExistentialQuantification #-}
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