module Main exposing (..)

import Html


type Maybe a
    = Just a
    | Nothing


mapMaybe : (a -> b) -> Maybe a -> Maybe b
mapMaybe f perhaps =
    case perhaps of
        Nothing ->
            Nothing

        Just a ->
            Just (f a)


maybeToList : (a -> b) -> List (Maybe a) -> List b
maybeToList f perhaps =
    case perhaps of
        x :: xs ->
            let
                result =
                    mapMaybe f x
            in
                case result of
                    Nothing ->
                        maybeToList f xs

                    Just a ->
                        a :: maybeToList f xs

        [] ->
            []


main : Html.Html a
main =
    Html.text <|
        case test of
            [ 2, 4 ] ->
                "pass"

            _ ->
                "fail"


succ : Int -> Int
succ =
    (+) 1


test : List Int
test =
    let
        maybe_list =
            [ Just 1, Nothing, Just 3, Nothing ]
    in
        maybeToList succ maybe_list