Reverse Polish Notation

RPN.fs

let (|Operator|_|) s =
    match s with
    | "+" -> Some (+)
    | "-" -> Some (-)
    | "*" -> Some (*)
    | "/" -> Some (/)
    | _ -> None

let eval state input =
    match input, state with
    | Operator o, o2 :: o1 :: tail -> o o1 o2 :: tail
    | _ -> int input :: state

let compute (s:string) = 
    s.Split([|' '|]) |> Seq.fold eval []

compute "1"
compute "1 2 +"
compute "5 4 - 1 -"
compute "5 4 1 - -"
compute "5 1 2 + 4 * + 3 -"