Mario Ice-Skating (first Elm code)

ice-skating-mario

import Color (..)
import Graphics.Collage (..)
import Graphics.Element (..)
import Keyboard
import Signal
import Time (..)
import Window

-- MODEL
mario = { x=0, y=0, vx=0, vy=0, dir="right" }


-- UPDATE -- ("m" is for Mario)
jump {y} m = if y > 0 && m.y == 0 then { m | vy <- 5 } else m
gravity dt m = if m.y > 0 then { m | vy <- m.vy - dt/4 } else m
physics dt m = { m | x <- m.x + dt*m.vx , y <- max 0 (m.y + dt*m.vy) }
skate {x} m = { m | vx <- if | abs x > 0 && m.y == 0 -> dash m.vx x
                             | m.y > 0               -> m.vx
                             | otherwise             -> drag m.vx
                  , dir <- if x < 0 then "left"  else
                           if x > 0 then "right" else m.dir }
                           
step (dt, keys) = jump keys >> gravity dt >> skate keys >> physics dt

-- Skate Update Functions
dash vx x = let newVx = vx + toFloat x * 0.05
            in  if abs newVx > 5 then vx else newVx
drag vx = if abs vx < 0.02 then 0 else vx - amount vx
amount vx = 0.01 * if vx > 0 then 1 else if vx < 0 then -1 else 0


-- DISPLAY
render (w',h') mario =
  let (w,h) = (toFloat w', toFloat h')
      verb = if | mario.y  >  0 -> "jump"
                | mario.vx /= 0 -> "walk"
                | otherwise     -> "stand"
      src = "http://elm-lang.org/imgs/mario/" ++ verb ++ "/" ++ mario.dir ++ ".gif"
  in collage w' h'
      [ rect w h  |> filled (rgb 174 238 238)
      , rect w 50 |> filled (rgb 74 163 41)
                  |> move (0, 24 - h/2)
      , toForm (image 35 35 src) |> move (mario.x, mario.y + 62 - h/2)
      ]

-- MARIO
input = let delta = Signal.map (\t -> t/20) (fps 300)
        in  Signal.sampleOn delta (Signal.map2 (,) delta Keyboard.arrows)

main = Signal.map2 render Window.dimensions (Signal.foldp step mario input)