Sorry, that I came up again with such an old bug (a pity it isn't fixed yet) http://www.cs.york.ac.uk/fp/nhc98/nhc-users-archive/0107.html Christian I wrote:
No default for MutualRecursion.PP at 23:1-24:18.(174,[(148,187)]) No default for MutualRecursion.PP at 19:1-20:18.(183,[(148,186)])
-- --------------------------------------------------------------------
module MutualRecursion where
data A a = A a | BasA (B a)
data B a = B a | AasB (A a)
class PP a where pp :: a -> String
instance PP a => PP (A a) where pp (A a) = pp a pp (BasA b) = pp b
instance PP a => PP (B a) where pp (B a) = pp a pp (AasB b) = pp b
fA :: PP a => A a -> String fA (A a) = pp a fA (BasA b) = fB b
fB :: PP a => B a -> String fB (B b) = pp b fB (AasB a) = fA a