Sorted.fsx

//#load "Spirograph.fs"
open System.Drawing
//open FSharp.TV.Spirograph

let round (x:float) = int (System.Math.Round (x))

module Seq = 
  let repeat items = 
    seq { while true do for item in items do yield item }


type Turtle = {
    position: (int*int);
    direction: float;
    bitmap: Bitmap;
    color: Color;
    drawing: bool
}

let save filename turtle = 
    turtle.bitmap.Save(filename)
    turtle

let dot x y turtle = 
    turtle.bitmap.SetPixel(x, y, turtle.color)
    turtle

let line x y turtle =
    let x0, y0 = turtle.position
    let dx = x-x0
    let dy = y-y0
    let xs = if dx > 0 then [ for ix in [x0..x] -> (ix, y0+(ix-x0)*dy/dx) ] else []
    let ys = if dy > 0 then [ for iy in [y0..y] -> (x0+(iy-y0)*dx/dy,iy) ] else []
    let dots = Seq.map (fun (x,y) -> dot x y) (Seq.append xs ys) //[for (x,y) in (Seq.append xs ys) -> dot x y ]
    {Seq.fold (fun turtle fn -> fn turtle) turtle dots with position = (x,y)}
            
let move (distance:int) turtle =
    let x, y = turtle.position
    let xd, yd = round (float distance * cos turtle.direction), round (float distance * sin turtle.direction)
    let nx, ny = x+xd, y+yd
    if turtle.drawing then 
        line nx ny turtle
    else
        {turtle with position = (nx, ny)}

let teleport (x:int) (y:int) (turtle:Turtle) =
    {turtle with position = (x,y)}

let penUp (ttl:Turtle) = {ttl with drawing = false}
let penDown (ttl:Turtle) = {ttl with drawing = true}
    

let dashMove (distance:int) turtle =
    let dashlength = 5
    let cmds = [penDown; move dashlength; penUp; move dashlength]
    let numcmds = distance*(Seq.length cmds)/(dashlength*2)
    let todo = Seq.take numcmds (Seq.repeat cmds)
    Seq.fold (fun ttl cmd -> cmd ttl) turtle todo

let setColor color ttl = {ttl with color = color}
                
let newTurtle (x:int) (y:int) = {
    position = (0,0); 
    direction = 0.0; 
    bitmap = new Bitmap(x,y); 
    color=Color.Black; 
    drawing=true
}

let clockwise rads (turtle:Turtle) = 
    {turtle with direction = turtle.direction + rads}

newTurtle 100 100
    |> teleport 50 50
    |> setColor Color.Red
    |> dashMove 50
    |> save (__SOURCE_DIRECTORY__ + "/foo.png")