%%%-------------------------------------------------------------------
%%% @author eryks
%%% @copyright (C) 2019, <COMPANY>
%%% @doc
%%%
%%% @end
%%% Created : 13. mar 2019 14:07
%%%-------------------------------------------------------------------
-module(onp).
-author("eryks").

%% API
-export([onp/1]).

onp(List) ->
  Elements = string:tokens(List, " "),
  [Head | Tail] = Elements,
  onp(Tail, [Head]).

onp([Head | Tail], Stack) ->
  case Head of
    "+" ->
      [One | OneStack] = Stack,
      [Two | TwoStack] = OneStack,
      NewResult = list_to_integer(Two) + list_to_integer(One),
      ThreeStack = [integer_to_list(NewResult) | TwoStack],
      onp(Tail, ThreeStack);
    "*" ->
      [One | OneStack] = Stack,
      [Two | TwoStack] = OneStack,
      NewResult = list_to_integer(Two) * list_to_integer(One),
      ThreeStack = [integer_to_list(NewResult) | TwoStack],
      onp(Tail, ThreeStack);
    "-" ->
      [One | OneStack] = Stack,
      [Two | TwoStack] = OneStack,
      NewResult = list_to_integer(Two) - list_to_integer(One),
      ThreeStack = [integer_to_list(NewResult) | TwoStack],
      onp(Tail, ThreeStack);
    "/" ->
      [One | OneStack] = Stack,
      [Two | TwoStack] = OneStack,
      NewResult = list_to_integer(Two) div list_to_integer(One),
      ThreeStack = [integer_to_list(NewResult) | TwoStack],
      onp(Tail, ThreeStack);
    "sqrt" ->
      [One | OneStack] = Stack,
      NewResult = math:sqrt(list_to_integer(One)),
      NewerResult = NewResult,
      TwoStack = [float_to_list(NewerResult) | OneStack],
      onp(Tail, TwoStack);
    _ -> onp(Tail, [Head | Stack])
  end;

onp([], [Last]) ->
  Last.