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F# in Hex
f#

I wrote this F# snippet and I had an error!

open System.Drawing

open System.Windows.Forms

let Hex (x, y) =

let point1 = new Point(x, y)

let point2 = new Point(x + 20, y)

let point3 = new Point(x + 40, y + 20)

let point4 = new Point(x + 60, y + 20)

let point5 = new Point(x + 80, y)

let hexPoint = [| point1; point2; point3; point4; point5; |]

hexPoint

let form =

let temp = new Form()

temp.Resize.Add(fun _ -> temp.Invalidate())

let mutable x = 0

let mutable y = 0

let hexPoint = Hex (x, y)

temp.Paint.Add(fun e -> e.Graphics.DrawPolygon(Pens.Red, hexPoint))

for i = 1 to 10 do

x <- x + 80

hexPoint <- Hex (x, y)

temp.Paint.Add(fun e -> e.Graphics.DrawPolygon(Pens.Red, hexPoint))

temp

Application.Run(form)

.

If you want to draw multiple points, you should use

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  let form = 
    let temp = new Form()
    temp.Resize.Add(fun _ -> temp.Invalidate())
    let mutable x = 0
    let mutable y = 0
    let hexPoint = Hex (x, y)
    temp.Paint.Add(fun e -> e.Graphics.DrawPolygon(Pens.Red, hexPoint))
    for i = 1 to 10 do
      x <- x + 80
      let tmpHexpoint = Hex (x, y) //temporary variable
      temp.Paint.Add(fun e -> e.Graphics.DrawPolygon(Pens.Red, tmpHexpoint))
    temp

By default, variables are not mutables. If you wanted to make hexpoint variable, you should have defined it with ref 

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let hexpoint = ref <| Hex(x,y)

But by doing so, your drawing would have failed because all polygons would refer to the same set of value (i.e. the ones in the last value assigned to hexpoint)

Hope this helps

By on 10/24/2008 1:40 PM ()

Thank-you!

By on 10/24/2008 4:08 PM ()

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