At 2001-01-16 14:36, Tom Pledger wrote:
Here's a similar example using type-substitution overlapping:
instance TheValue Char where ... instance Monad m => TheValue (m Char) where ... instance TheValue a => TheValue (Maybe a) where ...
trouble = theValue (Just 'b')
Apparently this is not good Haskell syntax. I tried compiling this in Hugs: class TheValue a where theValue :: a -> Int instance TheValue Char where theValue _ = 0 instance (Monad m) => TheValue (m Char) where theValue _ = 1 -- error here instance (TheValue a) => TheValue (Maybe a) where theValue _ = 2 trouble = theValue (Just 'b') I got a syntax error: (line 3): syntax error in instance head (variable expected) -- Ashley Yakeley, Seattle WA