Haskell Help

Haskell beginner here. Anybody know how i shrink this down a bit, sorry I'd figure out myself but i'm sick of learning the same concepts in 20 different languages.

{-

type Month = String

validMonth :: Month -> Bool
validMonth "January" = True
validMonth "February" = True
validMonth "March" = True
validMonth "April" = True
validMonth "May" = True
validMonth "June" = True
validMonth "July" = True
validMonth "August" = True
validMonth "September" = True
validMonth "October" = True
validMonth "November" = True
validMonth "December" = True
validMonth _ = False

-}

>>9

Nigger, the point about putting something as constant as the names of all of the months in an array variable as being fagishly stupid and terrible teaching was apt.