import Data.List (foldl') -- import the strict fold
-- number of steps
-type Step = Int
+type Distance = Int
+
+-- easting, northing
type Position = (Int, Int)
+-- the directions. See below for functions for turning
data Direction = North | East | South | West
deriving (Enum, Show, Bounded, Eq)
--- direction, easting, northing
+-- the currenct state of a Mowmaster
data Mowmaster = Mowmaster { direction :: Direction
, position :: Position
} deriving (Show, Eq)
-data Instruction = Forward Step
+-- one instruction for the mowmaster
+data Instruction = Forward Distance
| Clockwise
| Anticlockwise
| Comment String
executeAll = foldl' execute initialMowmaster
-
-- Is this line a comment?
isComment :: String -> Bool
isComment ('#':_) = True
readInstruction' _ t = Comment t
-initialMowmaster = Mowmaster North (0, 0)
+initialMowmaster = Mowmaster East (0, 0)
-- Calculate manhattan distance from start to this state
execute m Anticlockwise = m {direction = turnACW (direction m)}
execute m (Comment _) = m
+
-- Move in the current direction
-forward :: Int -> Direction -> Position -> Position
+forward :: Distance -> Direction -> Position -> Position
forward s North (e, n) = (e, n+s)
forward s South (e, n) = (e, n-s)
forward s West (e, n) = (e-s, n)
forward s East (e, n) = (e+s, n)
-
-- | a `succ` that wraps
turnCW :: (Bounded a, Enum a, Eq a) => a -> a
turnCW dir | dir == maxBound = minBound