Mars rover in haskell

rover.hs

data Position = Position Int Int Direction
	deriving (Show, Eq, Read)
data Direction = N | E | W | S
	deriving (Show, Eq, Enum, Bounded, Read)
data Command = L | R | M
	deriving (Show, Eq, Enum, Bounded, Read)
	
data DeltaPosition = DeltaPosition Int Int
	
data State = State {
	leftDirection :: Direction,
	rightDirection :: Direction,
	delta :: DeltaPosition
}

toPosition input = (read ("Position " ++ input)) :: Position
toCommands input = map (\i -> (read [i]) :: Command) input

state N = (State W E (DeltaPosition 0 (-1)))
state W = (State S N (DeltaPosition (-1) 0))
state S = (State E W (DeltaPosition 0 1))
state E = (State N S (DeltaPosition 1 0))

add (Position x y d) (DeltaPosition x' y') = Position (x + x') (y + y') d

execute (Position x y d) L = Position x y (leftDirection (state d))
execute (Position x y d) R = Position x y (rightDirection (state d))
execute p@(Position x y d) M = add p (delta (state d))

route position commands = foldl execute (toPosition position) (toCommands commands)

-- route "1 2 N" "LRLRM"