Hi, I'm wondering why I have to repeat the class constraints at every function. If I got the data type
data (Eq a, Show a, Data a, Eq b, Show b, Data b, Eq c, Show c, Data c) => Foo a b c = Foo a b c
and then a function from Foo to String I have to supply the signature
bar :: (Eq a, Show a, Data a, Eq b, Show b, Data b, Eq c, Show c, Data c) => Foo a b c -> String
even though it should be clear that a, b and c *must* fulfill the constraints already so I should be able to just supply the signature
bar :: Foo a b c -> String
Another related problem I got is that even though I can create the type
type B = (Eq a, Show a, Data a, Eq b, Show b, Data b, Eq c, Show c, Data c) => Foo a b c
I cannot use it like
bar :: B -> String
so my type class constraints got a tendency become huge! It is possible to work around this somehow? I'm in a situation at the moment where I got a data type with four fields each with three constraints (Show, Eq, Data), so I have to repeat 12 constraints at every function signature... :( Finally is there some way to bundle type class constraints, something like
data {Eq, Show, Data} {a, b, c} => Foo a b c = Foo a b c -- make believe syntax
so I don't have to repeat every constraint and variable all the time? -- Oscar