module NonDet where

type L a = [a]

unitL :: a -> L a
unitL a = [a]

[]     `appendL` xs = xs
(x:xs) `appendL` ys = x : (xs `appendL` ys)

bindL :: L a -> (a -> L b) -> L b
(a:es) `bindL` k = k a  `appendL` (es `bindL` k)
[]     `bindL` k = []

tryL :: L a -> L a -> L a
tryL (v:vs) h = v : tryL vs h
tryL []     h = h 

failL :: String -> L a
failL _ = []