Could someone tell me why this is not allowed and if there is a possible
workaround. (I know this example seems pointless however it is a real
concern as having bulk types in the context is something I would really
like to do.)
class Listable c a where
toList :: c a -> [a]
class Find c a b where
find :: a -> c a b -> b
instance Listable [] a where
toList c = c
instance (Listable c (a,b)) => Find c a b where
find a c = lookup a (toList c)
$ hugs -98 test.hs
ERROR "test.hs" (line 11): Illegal type in class constraint
ghc -fglasgow-exts -fallow-undecidable-instances test.hs
test.hs:12:
Couldn't match `* -> *' against `*'
Expected kind: (* -> * -> *) -> * -> * -> *
Inferred kind: (* -> *) -> * -> * -> *
When checking kinds in `Find c a b'
--
Kevin Atkinson
[EMAIL PROTECTED]
http://metalab.unc.edu/kevina/
