gistfile1.txt

import Mouse
import Window

data Event = MouseUp | MouseDown | MouseMove Int Int
type Status = { mouseDown:Bool, points:[(Int, Int)] }

initialState : Status
initialState = Status False []

nextState : Event -> Status -> Status
nextState event state = case event of
                          MouseUp -> { state | mouseDown <- False }
                          MouseDown -> { state | mouseDown <- True }
                          MouseMove x y -> if state.mouseDown
                                           then { state | points <- (x,y)::state.points }
                                           else state

inputSignal : Signal Event
inputSignal = merges [ MouseMove <~ Mouse.x ~ Mouse.y
                     , (\b -> if b then MouseDown else MouseUp) <~ Mouse.isDown ]

currentState : Signal Status
currentState = foldp nextState initialState inputSignal

mousePosition : Int -> Int -> Int -> Int -> (Float, Float)
mousePosition x y w h = (toFloat x-(toFloat w/2), -(toFloat y)+(toFloat h/2))

main : Signal Element
main = let disp state w h =
            collage w h (map (\(x,y) -> move (mousePosition x y w h) <| filled red (circle 4)) state.points )
       in disp <~ currentState ~ Window.width ~ Window.height