Conditional branches of Haskell.

I'm studying Haskell.

Haskell has some conditional statements.

1. pattern matching

fact 0 = 1
fact n = n * fact (n-1)

2. guard

fact n | n==0 = 1
       | otherwise = n * fact (n-1)

3. if

fact n = if n==0 then 1
                 else n * fact (n-1)

4. case

fact n = case n of
           0 -> 1
           _ -> n * fact (n-1)