Reverse polish calculator in F#, derived from this 35-line Racket metaprogramming example http://beautifulracket.com/stacker/source-listing.html

ReversePolishCalculator.fs

let (|Float|_|) s =
  let mutable x = 0.0
  if System.Double.TryParse(s, &x) then Some x else None

let binop f x y stack =
  let z = f x y
  printfn "%A" z
  z::stack

let rec loop stack =
  match stdin.ReadLine(), stack with
  | Float x, stack -> x::stack
  | "+", x::y::stack -> binop (+) x y stack
  | "*", x::y::stack -> binop (*) x y stack
  | _ -> stack
  |> loop

do loop[]