katas-elm-taxicab

Main.elm

module Main exposing (..)

import String
import Html exposing (text)

type Turn 
    = L 
    | R 
    | Stay

type alias Instruction = 
    { turn: Turn
    , steps: Int
    }

type Direction 
    = North 
    | South 
    | East 
    | West

type alias Position = 
    { x: Int
    , y: Int
    , direction: Direction
    }

-- yay parsing!!!

input = """R3, L5, R2, L2, R1, L3, R1, R3, L4, R3, L1, L1, R1, L3, R2, L3, L2, R1, R1, L1, R4, L1, L4, R3, L2, L2, R1, L1, R5, R4, R2, L5, L2, R5, R5, L2, R3, R1, R1, L3, R1, L4, L4, L190, L5, L2, R4, L5, R4, R5, L4, R1, R2, L5, R50, L2, R1, R73, R1, L2, R191, R2, L4, R1, L5, L5, R5, L3, L5, L4, R4, R5, L4, R4, R4, R5, L2, L5, R3, L4, L4, L5, R2, R2, R2, R4, L3, R4, R5, L3, R5, L2, R3, L1, R2, R2, L3, L1, R5, L3, L5, R2, R4, R1, L1, L5, R3, R2, L3, L4, L5, L1, R3, L5, L2, R2, L3, L4, L1, R1, R4, R2, R2, R4, R2, R2, L3, L3, L4, R4, L4, L4, R1, L4, L4, R1, L2, R5, R2, R3, R3, L2, L5, R3, L3, R5, L2, R3, R2, L4, L3, L1, R2, L2, L3, L5, R3, L1, L3, L4, L3"""

split : String -> List String
split text = String.split ", " text

turn_from_string : String -> Turn
turn_from_string text = case text of
    "L" -> L
    "R" -> R
    _ -> Stay

instruction_from_string : String -> Instruction
instruction_from_string text = 
    let
        turnString = String.left 1 text
        numSteps = String.dropLeft 1 text
    in
       {turn = turn_from_string turnString, steps = Result.withDefault 0 (String.toInt numSteps)}

instructions_from_string : String -> List Instruction
instructions_from_string text =
    List.map instruction_from_string (split text)

--

make_turn : Direction -> Turn -> Direction
make_turn direction turn =
    case turn of
        L ->
            case direction of
                North -> West
                West -> South
                South -> East
                East -> North
        R ->
            case direction of
                North -> East
                East -> South
                South -> West
                West -> North
        Stay -> direction


make_move : Instruction -> Position -> Position
make_move {turn, steps} {x, y, direction} =
    let
        new_direction = make_turn direction turn 
        (new_x, new_y) =
            case new_direction of
                North -> (x, y + steps)
                East -> (x + steps, y)
                South -> (x, y - steps)
                West -> (x - steps, y)
    in
       {x = new_x, y = new_y, direction = new_direction }

initialPosition = {x=0, y=0, direction=North}

main =
    let
        instructions = instructions_from_string input
        endPosition = List.foldl make_move initialPosition instructions
        distance = endPosition.x + endPosition.y
    in
        text ("distance = " ++ (toString distance))