Code solution for Advent of Code 2017 Day 1 (http://adventofcode.com/2017/day/1)

advent-of-code-2017-elm-day1.elm

module Main exposing (main)

import Html exposing (Html, li, text, ul)
import Html.Attributes exposing (style)

-- Advent of Code 2017 - Day 1 (http://adventofcode.com/2017/day/1)
-- https://ellie-app.com/hBMTrVXyna1/1

main : Html msg
main =
    ul []
        (List.map
            (\c ->
                let
                    result =
                        dayOneFacade (Tuple.first c)
                in
                result
                    |> toString
                    |> (\s ->
                            "Expected "
                                ++ toString (Tuple.second c)
                                ++ " got "
                                ++ s
                                |> text
                                |> (\t ->
                                        li
                                            [ style
                                                [ ( "background"
                                                  , if result == Tuple.second c then
                                                        "green"
                                                    else
                                                        "red"
                                                  )
                                                ]
                                            ]
                                            [ t ]
                                   )
                       )
            )
            cases
        )


cases =
    [ ( "1122", 3 ), ( "1111", 4 ), ( "1234", 0 ), ( "91212129", 9 ) ]


dayOneFacade : String -> Int
dayOneFacade digits =
    let
        dayOne : List Int -> Int -> Int
        dayOne list sum =
            case list of
                a :: b :: tail ->
                    dayOne (b :: tail)
                        (if a == b then
                            sum + b
                         else
                            sum
                        )

                _ ->
                    sum

        list =
            String.split "" digits
                |> List.map (String.toInt >> Result.toMaybe >> Maybe.withDefault 0)
                |> (\ints -> ints ++ List.take 1 ints)
    in
    dayOne list 0