Gravity and Ball

gravity.elm

-- https://gist.github.com/davidhq/eae55136adc1973b524f7b41746b78ac
import Graphics.Collage exposing (..)
import Graphics.Element exposing (..)
import Color exposing (..)
import Keyboard
import Time
import Debug

-- Model
type alias Model = { x : Float, y : Float, radius: Float }

width : Int
width = 700

height : Int
height = 500

bottom : Int
bottom = (-height) // 2

-- Update

type Action = Up | Right | Left | Noop

update : Action -> Model -> Model
update action model =
  playerMovement action model
    |> gravity
    |> Debug.watch "model"

playerMovement : Action -> Model -> Model
playerMovement action model =
  case action of
    Noop -> model
    Up -> { model | y = model.y + 30 }
    Right -> { model | x = model.x + 5 }
    Left -> { model | x = model.x - 5 }

gravity : Model -> Model
gravity model =
  if model.y > (toFloat bottom) + model.radius
  then { model | y = model.y - 5 }
  else model

-- View

view : Model -> Element
view model =
  let
    ball =
      circle model.radius
        |> filled blue
        |> move (model.x, model.y)
        |> Debug.trace "ball"
    background =
      rect (toFloat width) (toFloat height)
        |> filled green
  in
    collage width height [ ball ]


-- Signals

input : Signal { x : Int, y : Int }
input =
  Signal.sampleOn (Time.fps 30) Keyboard.arrows

action : Signal Action
action =
  Signal.map arrowToAction input

arrowToAction : { x : Int, y : Int} -> Action
arrowToAction arrow =
    if arrow.x < 0 then Left else
    if arrow.x > 0 then Right else
    if arrow.y > 0 then Up else Noop

model : Signal Model
model =
  Signal.foldp update {x = 0, y = 0, radius = 30 } action

-- Signal.foldp
--    :  (a -> state -> state)
--   -> state
--   -> Signal a
--   -> Signal state

main : Signal Element
main =
  Signal.map view model

Updated for Elm 0.16