collatz/Main.elm

module Collatz exposing (..)

import Html exposing (..)
import Html.Events exposing (..)
import Html.Attributes exposing (id, class, style)

import Hex

type alias Model =
    {
    }

initModel : Model
initModel =
    {
    }


type Msg
    = NoOp

box : Int -> List Int -> Html Msg
box n p =
    let
        truval = List.length p
        val = round (atan (toFloat truval) * 2670177)
        code = "#" ++ (String.padLeft 6 '0' (Hex.toString val))
        fore =
            if truval < 127 then
                "#ffffff"
            else
                "#000000"
    in
        div
            [ class "box"
            , style
                [ ("background-color", code)
                , ("color", fore)
                ]
            ]
            [ text (toString n) ]

collatzSteps : Int -> Int
collatzSteps n =
    let
        inner (n, c) =
            case n of
                1 ->
                    (n, c)
                _ ->
                    if (rem n 2) == 0 then
                        inner ((n // 2), (c + 1))
                    else
                        inner ((n * 3 + 1), (c + 1))
        (one, steps) = inner (n, 0)
    in
        steps

collatzPath : Int -> List Int
collatzPath n =
    let
        helper n p =
            case n of
                1 ->
                    (n :: p)
                _ ->
                    if (rem n 2) == 0 then
                        helper (n // 2) (n :: p)
                    else
                        helper (n * 3 + 1) (n :: p)
    in
        helper n []

view : Model -> Html Msg
view model =
    div
        []
        <|
        List.map (\n -> (box n (collatzPath n))) (List.range 1 777)

update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
    ( model, Cmd.none )

--subscriptions : Model -> Sub Msg
--subscriptions model =
--    Sub.batch
--        [
--        ]

main =
    Html.program
        { init = (initModel, Cmd.none)
        , view = view
        , update = update
        , subscriptions = \_ -> Sub.none
        }