Working example (from Xamarin Studio) demonstrating Type Variants and discriminated unions

typeVariantsDemo

open Microsoft.FSharp.Math
type Shape = 
  | Circle of radius:float
  | Rectangle of width:float * height:float // tuple of float, float
  | Triangle of tbase:float * height:float

let area shape = 
  match shape with
  | Circle radius -> Math.PI * radius * radius
  | Rectangle (width, height) -> width * height
  | Triangle (tbase, height) -> 0.5 * tbase * height

let cshape = Circle(10.)
printfn "Circle Area: %f" (area cshape)

let rshape = Rectangle(3., 7.)
printfn "Rect Area: %f" (area rshape)

let tshape = Triangle(3., 7.)
printfn "Triangle Area: %f" (area tshape)

(*
Console output for the above
Circle Area: 314.159265
Rect Area: 21.000000
Triangle Area: 10.500000
*)

This was my taking the second example from Luketopia's slides on OO vs Discriminated Unions. I just changed it to rename things in case people mis-read his code and renamed a variable base so quoting wasn't necessary.