Haskell version using megaparsec

[summerofcode2018soln.git] / src / task1 / task1-mpc.hs

diff --git a/src/task1/task1-mpc.hs b/src/task1/task1-mpc.hs
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+{-# LANGUAGE OverloadedStrings #-}
+
+import Data.List (foldl')        -- import the strict fold
+
+import Data.Text (Text)
+-- import qualified Data.Text as T
+import qualified Data.Text.IO as TIO
+
+import Data.Void (Void)
+
+import Text.Megaparsec -- hiding (State)
+import Text.Megaparsec.Char
+import qualified Text.Megaparsec.Char.Lexer as L
+import qualified Control.Applicative as CA
+
+
+-- number of steps
+type Distance = Int
+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
+data Mowmaster = Mowmaster { direction :: Direction 
+                           , position :: Position
+                           } deriving (Show, Eq)
+
+-- one instruction for the mowmaster
+data Instruction =   Forward Distance
+                   | Clockwise 
+                   | Anticlockwise
+                   | Comment String
+    deriving (Show, Eq)
+
+
+main :: IO ()
+main = do 
+        instruction_text <- TIO.readFile "data/01-mowmaster.txt"
+        let instructions = successfulParse instruction_text
+        print $ part1 instructions
+        print $ part2 instructions
+
+part1 :: [Instruction] -> Int
+part1 = length 
+
+part2 :: [Instruction] -> Int
+part2 instructions = finalDistance $ executeAll instructions
+    where executeAll = foldl' execute initialMowmaster
+
+initialMowmaster = Mowmaster North (0, 0)
+
+
+-- Calculate manhattan distance from start to this state
+finalDistance :: Mowmaster -> Int
+finalDistance m = (abs e) + (abs n)
+    where (e, n) = position m
+
+
+-- Make one move
+execute :: Mowmaster -> Instruction -> Mowmaster
+execute m (Forward s)    = m {position  = forward s (direction m) (position m)}
+execute m  Clockwise     = m {direction = turnCW (direction m)}
+execute m  Anticlockwise = m {direction = turnACW (direction m)}
+execute m  _ = m
+
+-- Move in the current direction
+forward :: Int -> 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
+           | otherwise       = succ dir
+
+-- | a `pred` that wraps
+turnACW :: (Bounded a, Enum a, Eq a) => a -> a
+turnACW dir | dir == minBound = maxBound
+            | otherwise       = pred dir
+
+
+-- Parse the input file
+
+type Parser = Parsec Void Text
+
+-- treat comment lines as whitespace
+sc :: Parser ()
+sc = L.space space1 lineComment CA.empty
+    where lineComment = L.skipLineComment "#"
+
+lexeme  = L.lexeme sc
+integer = lexeme L.decimal
+symb = L.symbol sc
+
+-- instructions is some optional space followed by many instructions
+instrsP = optional sc *> many instrP
+instrP = forwardP <|> cwP <|> acwP
+
+-- parse each instruction
+forwardP = Forward <$> (symb "F" *> integer)
+cwP = Clockwise <$ symb "C"
+acwP = Anticlockwise <$ symb "A"
+
+successfulParse :: Text -> [Instruction]
+successfulParse input = 
+        case parse instrsP "input" input of
+                Left  _error -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
+                Right instrs  -> instrs
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