-module(rpn_calc).
-export([eval/1, eval/2]).
-vsn('0.2').
-author('Julian Fondren <miprihas@yahoo.com>').
-license('No-advertise-clause BSD').

eval(S) -> eval(S, []).
eval(S, Stack) -> rpn(lists:map(fun parse/1, lex(S)), Stack).

rpn([], Stack) -> Stack;
rpn([{lit, X}|T], Stack) -> rpn(T, [X|Stack]);
rpn([{op, Op}|T], [A,B|Stack]) -> rpn(T, [op(Op, A, B)|Stack]).

op('-', A, B) -> B - A;
op('/', A, B) -> B / A;
op(Op, A, B) -> erlang:Op(A,B).

lex(S) -> {ok, Es} = regexp:split(S, "\s"), Es.

parse(S) when list(S) ->
    case (catch list_to_integer(S)) of
        {'EXIT',_} -> case (catch list_to_float(S)) of
                          {'EXIT',_} -> {op, list_to_atom(S)};
                          F -> {lit, F}
                      end;
        N -> {lit, N}
    end.