Scala's flatMap is not Haskell's >>=

August 23, 2012

The behaviour of flatMap in Scala:

scala> List(1, 2, 3, 4) flatMap (Some(_))
res0: List[Int] = List(1, 2, 3, 4)

The behaviour of >>= in Haskell:

> [1, 2, 3, 4] >>= Just

<interactive>:4:18:
    Couldn't match expected type `[b0]' with actual type `Maybe a0'
    Expected type: a0 -> [b0]
      Actual type: a0 -> Maybe a0
    In the second argument of `(>>=)', namely `Just'
    In the expression: [1, 2, 3, 4] >>= Just