kempe-0.2.0.7: lib/either.kmp

; I'm not sure how useful this module is but I have it as a test for the
; typechecker and I guess to show how pattern matching works.

type Either a b { Left a | Right b }

fromRight : b ((Either a) b) -- b
          =: [
    { case
        | Left  -> drop
        | Right -> dip(drop)
    }
]

join : ((Either a) ((Either a) b)) -- ((Either a) b)
     =: [
    { case
        | Left  -> Left
        | Right ->
    }
]

isLeft : ((Either a) b) -- Bool
       =: [
    { case
        | Left  -> drop True
        | Right -> drop False
    }
]

isRight : ((Either a) b) -- Bool
        =: [
    { case
        | Right -> drop True
        | Left  -> drop False
    }
]