drunkenWalk.hs

import Data.List

data Dir = N | S | E | W deriving (Eq, Show)
type Coord = (Int, Int)

(|+|) (x,y) (x',y') = (x+x',y+y')
infixl 6 |+|

toDelta d = case d of
  N -> (0, -1)
  S -> (0, 1)
  E -> (1, 0)
  W -> (-1, 0)

toPath = reverse . foldl' (\p c -> head p |+| c : p) [(0,0)]

halts = isDistinct . toPath . map toDelta
  where isDistinct xs = xs == nub xs

walk = [N, N, E, E, S, S, W, W]
walk2 = [N, N, N, N, N, N, N, N, N, N]

{-
> halts walk
False
> halts walk2
True
-}