Why does pattern matching not cover list heads in Haskell? [duplicate]

Question

I want to use the following code/ functionality in Haskell:

test :: String -> String -> Bool
test (x:xs) (x:ys) = True
test _        _    = False

This should check if both lists begin with exactly the same element.
But this does not work.
My compiler says: Conflicting definitions for x

I thought a pattern matching like this had to work in a functional language. I just worked with Prolog before and I'm pretty sure it worked there :/

Is this not implemented in Haskell or is my Syntax wrong?

Answer 1

You probably wants something like that.

test :: String -> String -> Bool
test (x:xs) (y:ys) = x == y
test _        _    = False

As @TikhonJelvis noticed, haskell is not a Prolog, so you can't check the equality of the variables inside pattern matching.

Answer 2

Pattern matching doesn't unify variables.

test :: String -> String -> Bool
test (x:xs) (y:ys) = x == y
test _        _    = False

So you can test each variable for equality separately, as above.