2011-11-08 14:59, Felipe Almeida Lessa skrev:
On Tue, Nov 8, 2011 at 11:49 AM, Anupam Jain wrote:
I can work around this by changing my data type declaration to include Show
constraints but I don't want to restrict my data type to only Showable
things just so I could have a "Show" instance for
Hi,
Anupam Jain wrote:
-- My datatype
data T o where
Only ∷ o → T o
TT ∷ T o1 → (o1 → o2) → T o2
-- Show instance for debugging
instance Show o ⇒ Show (T o) where
show (Only o) = "Only " ⊕ (show o)
show (TT t1 f) = "TT (" ⊕ (show t1) ⊕ ")"
As you noticed, the last line doesn't wor
On Tue, Nov 8, 2011 at 11:49 AM, Anupam Jain wrote:
> While I understand why I get this error, I have no idea how to fix it! I
> cannot put a Show constraint on o1 because that variable is not exposed in
> the type of the expression.
That means 'o1' is an existencial variable.
> I can work aroun
Hi all,
I was trying to do something very simple with GADTs when I ran into this
problem -
-- My datatype
data T o where
Only ∷ o → T o
TT ∷ T o1 → (o1 → o2) → T o2
-- Show instance for debugging
instance Show o ⇒ Show (T o) where
show (Only o) = "Only " ⊕ (show o)
show (TT t1 f) = "TT (
