Call-by-name semantics in F#

call-by-name.fsx

open System
let rnd = Random()
let randint<'a> = 
    print "generating random number"
    rnd.Next(0,10)

type Signal = Signal with
    member __.Return x = x
    member __.Delay (f:unit -> _) = f

let a = Signal { return randint }
let b = Signal { return randint }
let c = Signal { return a() + b() }

[for _ in 1..10 -> c ()]    // [6; 12; 6; 14; 9; 12; 1; 10; 16; 8]