open System
let evalRpnExpr (s : string) =
let solve items current =
match (current, items) with
| "+", y::x::t -> (x + y)::t
| "-", y::x::t -> (x - y)::t
| "*", y::x::t -> (x * y)::t
| "/", y::x::t -> (x / y)::t
| _ -> (float current)::items
(s.Split(' ') |> Seq.fold solve []).Head
[<EntryPoint>]
let main argv =
[ "4 2 5 * + 1 3 2 * + /"
"5 4 6 + /"
"10 4 3 + 2 * -"
"2 3 +"
"90 34 12 33 55 66 + * - + -"
"90 3 -" ]
|> List.map (fun expr -> expr, evalRpnExpr expr)
|> List.iter (fun (expr, result) -> printfn "(%s) = %A" expr result)
Console.ReadLine() |> ignore
0 // return an integer exit code
