F# pattern matching sample

program.fs

// Learn more about F# at http://fsharp.org

type Shape =
    | Rectangle of width : float * length : float
    | Circle of radius : float
    | Prism of width : float * float * height : float

let rect = Rectangle(length = 1.3, width = 10.0)
let circ = Circle(1.0)

let getShapeHeight (shape: Shape) :float = 
    match shape with
    | Rectangle(width = h) -> h
    | Circle(radius = r) -> 2. * r

[<EntryPoint>]
let main argv =
    let foo = getShapeHeight rect
    printfn "Hello!"
    0 // return an integer exit code

Remove line 6 above and try to compile this. It will be happy. Add the line 6 back and compile, you will get a warning like below: