Start of work of a gui for drawing graphs in elm

Graph.elm

module Counter where

import Array
import Graphics.Element exposing (..)
import Graphics.Collage exposing (..)
import Color exposing (..)
import Mouse


-- MODEL

type alias Point = (Float,Float)
type alias Points = Array.Array Point
type alias Arrow = (Point,Point)
type alias Model = {
  points: Points,
  arrows: List (Int,Int),
  curLineStart: Maybe Point,
  mouse: Point
}

startModel = {
  points=Array.fromList [(0,0), (10,-200)],
  arrows=[(0,1)],
  curLineStart = Nothing,
  mouse = (0,0)
 }

-- UPDATE

type Action = Pressed Bool | Move Point

update : Action -> Model -> Model
update action model =
  case action of
    Pressed isdown -> {model |
                  points = Array.push model.mouse model.points}
    Move p -> {model | mouse = p}


-- VIEW
w = 500
h = 500

view : Model -> Element
view model =
  collage w h
          ((List.map showPoint <| Array.toList model.points) ++
          (List.map (showArrow model.points) model.arrows))

showPoint: (Float, Float) -> Form
showPoint point = circle 10
                  |> filled red
                  |> move point

showArrow : Points -> (Int,Int) -> Form
showArrow points (a,b) =
  let getPoint n = Maybe.withDefault (0,0) (Array.get n points)
      (p,q) = (getPoint a, getPoint b) in
    segment p q
    |> traced defaultLine

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

mousepos = Signal.map convertCoords Mouse.position

main =
  Signal.foldp update startModel
   (Signal.mergeMany [Signal.map Move mousepos, Signal.map Pressed Mouse.isDown])
  |> Signal.map view