Pattern matching variables in a case statement in Haskell

Question

If I compare a string literal to a string literal using the case statement, I get the expected behavior: if they are the same - it matches, if they are not - it does not.

Answer 1

See Don's answer for why. A common idiom for doing what you are trying to do is this:

var1 = "abc"
var2 = "def"

foo x = case () of
    () | x == var1 -> "Fail"
       | x == var2 -> "Failzor"
       | otherwise -> "WIN"

Of course in this case we would lose the case and just write the guards directly on the function:

foo x | x == var1 = "Fail"
      | ...

UPDATE

These days the MultiWayIf extension does this with slightly less syntactic noise.

{-# LANGUAGE MultiWayIf #-}

foo x = if | x == var1 -> "Fail"
           | x == var2 -> "Failzor"
           | otherwise -> "WIN"