Haskell surprised me again

blog.md

This time it is case expression. I was looking for a way in haskell to define constants so I wrote this:

one = 1
two = 2
three = 3

which n =
  case n of
    one -> "one"
    two -> "two"
    three -> "three"
    _ -> "unknown"

Compiler warned me that there were overlapped patterns. I only realized what the warning meant after a while. one, two and three in case patterns must have shadowed the definitions at the beginning of the file. Using guards worked:

one = 1
two = 2
three = 3

which n =
  case n of
    _ | n == one -> "one"
    _ | n == two -> "two"
    _ | n == three -> "three"
    _ -> "unknown"