Functional Kats Robot simulator kata

Lib.hs

module Lib where

import Control.Arrow (first, second)

data Dir = N | E | S | W deriving (Show, Enum, Bounded)

type Pos = (Int, Int)

data Robot = Robot Dir Pos deriving Show

right :: Dir -> Dir
right W = N
right d = succ d

left :: Dir -> Dir
left N = W
left d = pred d

-- Dir is direction robot currently facing
advance :: Dir -> Pos -> Pos
advance N = second succ
advance E = first succ
advance S = second pred
advance W = first pred

interpretC :: Char -> Robot -> Robot
interpretC 'R' (Robot d p) = (Robot (right d) p)
interpretC 'L' (Robot d p) = (Robot (left d) p)
interpretC 'A' (Robot d p) = (Robot d (advance d p))
interpretC _ _ = error "undefined movement command"

interpretS :: String -> Robot -> Robot
interpretS s r = foldl (flip interpretC) r s

test :: IO ()
test = do
  let r = Robot N (7,3)
  let r' = interpretS "RAALAL" r
  print r'