What the fuck, Haskell?

Prelude Data.List> :t isInfixOf
isInfixOf :: (Eq a) => [a] -> [a] -> Bool
Prelude Data.List> let f = isInfixOf
Prelude Data.List> :t f
f :: [()] -> [()] -> Bool

This isn't a huge deal and I know I can just tell it the type signature explicitly, but why does this happen?

Why do we need Haskell, when we have C++? You can concieve buttugly ideas, using C++ templates category theory. And writing C++ already requires PhD and years of learning.