Part 2: Following Elm tutorial

tutorial.elm

import Graphics.Element exposing (..)
import Graphics.Collage exposing (..)
import Color exposing (..)
import Mouse
import Window
import Time exposing (..)
import Signal exposing (foldp)

--Model

type alias Vec = 
  (Float, Float)
  
type alias Pill = 
  { pos : Vec
   , vel : Vec
   , rad : Float
   , col : Color
   }

vecAdd : Vec -> Vec -> Vec
vecAdd (ax, ay) (bx, by) = 
  (ax + bx, ay + by)

vecMulS : Vec -> Time -> Vec
vecMulS (x, y) t = 
  (x*t, y*t)
  
defaultPill = 
   { pos = (0,0)
   , vel = (0,-30)
   , rad = 15
   , col = lightRed
   }
    
-- Update

stepPill : Time -> Pill -> Pill  
stepPill dt p = 
  {p|pos = vecAdd p.pos (vecMulS p.vel dt)}


-- View
render : (Int, Int) -> Pill -> Element
render (w,h) p = 
  let formPill {rad, col, pos} = circle rad 
                                  |> filled col
                                  |> move pos
      forms = [formPill p]
                        
  in
  color lightGray  <| container w h middle
                   <| color white
                   <| collage 400 400 forms
sig = Signal.map inSeconds (fps 30)  
main = Signal.map2 render Window.dimensions (foldp stepPill defaultPill sig )