Hi all,
I wonder if anyone can help me find my error, in this code:
It’s note clear to me why x :: a is an error, except that maybe the type of f is not being correctly inferred?
Am I, maybe, not allowed to use pattern matching, on the right side of ‘=‘?
Thanks,
-db
data Stream a = Cons a (Stream a)
newtype StreamMap a b = SM (Stream a -> Stream b)
instance Arrow StreamMap where
where g (Cons x xs) = Cons (f x) (g xs)
SM f >>> SM g = SM (g . f)
first (SM g) = SM h -- h :: Stream (a, c) -> Stream (b, c)
where h :: Stream (a, c) -> Stream (b, c)
h (Cons (x, y) zs) = Cons ((f x), y) (h zs)
g :: Stream a -> Stream b
g (Cons x xs) = Cons (f x) (g xs)
Couldn't match expected type ‘b1’ with actual type ‘a’
‘a’ is a rigid type variable bound by the type signature for g :: interactive:IHaskell152.Stream a -> interactive:IHaskell152.Stream b1 at :10:17
‘b1’ is a rigid type variable bound by the type signature for g :: interactive:IHaskell152.Stream a -> interactive:IHaskell152.Stream b1 at :10:17
Relevant bindings include
xs :: interactive:IHaskell152.Stream a (bound at :11:27)
x :: a (bound at :11:20)
g :: interactive:IHaskell152.Stream a -> interactive:IHaskell152.Stream b1 (bound at :11:12)
In the first argument of ‘f’, namely ‘x’
In the first argument of ‘IHaskell152.Cons’, namely ‘(f x)’