Gravity and Ball

Ball.elm

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 -> Left
     | arrow.x > 0 -> Right
     | arrow.y > 0 -> Up
     | otherwise -> Noop

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

main : Signal Element
main =
  Signal.map view model

i'm new to elm, I tried running this gist with elm reactor but got this error:

`I cannot find module 'Graphics.Collage'.

Module 'Main' is trying to import it.

Potential problems could be:

• Misspelled the module name
• Need to add a source directory or new dependency to elm-package.json`

My elm-package looks like this:

{
"version": "1.0.0",
"summary": "helpful summary of your project, less than 80 characters",
"repository": "https://github.com/user/project.git",
"license": "BSD3",
"source-directories": [
"."
],
"exposed-modules": [],
"dependencies": {
"elm-lang/core": "5.0.0 <= v < 6.0.0",
"elm-lang/html": "2.0.0 <= v < 3.0.0",
"evancz/elm-graphics": "1.0.0 <= v < 2.0.0"
},
"elm-version": "0.18.0 <= v < 0.19.0"
}