Bugs item #1097046, was opened at 2005-01-06 09:47
Message generated for change (Settings changed) made by simonmar
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Category: Compiler (Type checker)
Group: 6.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Ashley Yakeley (ashley-y)
>Assigned to: Simon Peyton Jones (simonpj)
Summary: class context restrictions in GADT types not assumed
Initial Comment:
I think this should compile:
class C a where
f :: a -> Bool
data T a where
MkT :: (C a) => a -> T a
tf1 :: T Int -> Bool
tf1 (MkT aa) = f aa
tf2 :: T a -> Bool
tf2 (MkT aa) = f aa
tf1 does not give an error, but tf2 does. The type signature for tf2
should not need a class context, just as there's no "C Int" instance.
ThingEncoding.hs:32:23:
No instance for (C a)
arising from use of `f' at ThingEncoding.hs:32:23
Probable fix: Add (C a) to the type signature(s) for `tf2'
In the definition of `tf2': tf2 (MkT aa) = f aa
----------------------------------------------------------------------
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