open System

let rec parseAndCalcCore stack tokens =
    match tokens, stack with
    | [], [single] -> single
    | "+"::rest, h1::h2::tail -> parseAndCalcCore (h2 + h1::tail) rest
    | "-"::rest, h1::h2::tail -> parseAndCalcCore (h2 - h1::tail) rest
    | "/"::rest, h1::h2::tail -> parseAndCalcCore (h2 / h1::tail) rest
    | "*"::rest, h1::h2::tail -> parseAndCalcCore (h2 * h1::tail) rest
    | h::rest, _ -> parseAndCalcCore (((h |> double)::stack)) rest
    | _ -> failwith "The stack does not contains needed elements"
let parseAndCalc (expr : string) =
    expr.Split ' '
    |> Array.toList
    |> parseAndCalcCore []
    |> string
let print = parseAndCalc >> Console.WriteLine

[<EntryPoint>]
let main argv =
    print "1 1 +"
    print "2 -3 *"
    print "1 1 + 2 3 * -"
    print "1 3 / 2 *"
    print "10 1 2 + 2 + 5 + +"
    0