Fold not in scope

Question

Hello can someone explain to me why this custom implementaiton of foldl is not in scope?

afold::(a->b->a)->a->[b]->a
afold tsf accu (x:xs)=afold tsf (tsf accu x) xs
afold _ accu []=accu

I've tried running it like this :

afold (\x y-> show y:x) [] [1,2,3,4]

and i get the error:

Variable not in scope:
      afold :: ([String] -> () -> [String]) -> [a0] -> [Integer] -> t

When i try to use it even simpler like this :

 afold (\x y-> x+y) 0 [1,2,3,4]

i get the error:

 :: (Integer -> Integer -> Integer) -> Integer -> [Integer] -> t

Why isn't the output inferred?Why is it still t in the second example?

Answer 1

The problem was that i didn't place the method inside a module ,and load it.Once i enclosed the method in a module and loaded it in ghci it worked.

module Test where
afold::(a->b->a)->a->[b]->a
afold tsf accu (x:xs)=afold tsf (tsf accu x) xs
afold _ accu []=accu

In GHCI:

:load Test