f 0 = 0
f n = f n - 1

-module(rpn).
-export([rpn/1]).

rpn(Code) when is_list(Code) ->
  rpn(string:tokens(Code, " "), []).

rpn([], Stack) ->
  io:format("Result: ~B~n", [hd(Stack)]);

rpn([Token|Tail], Stack) ->
  rpn(Tail, token_execute(Token, Stack)).

token_execute("+", [Arg1,Arg2|Tail]) ->
  [Arg1 + Arg2|Tail];

token_execute("-", [Arg1,Arg2|Tail]) ->
  [Arg2 - Arg1|Tail];

token_execute("*", [Arg1,Arg2|Tail]) ->
  [Arg1 * Arg2|Tail];

token_execute("/", [Arg1,Arg2|Tail]) ->
  [Arg2 div Arg1|Tail];

token_execute("_", [Arg1|Tail]) ->

f :: Number -> Number
f(0) -> 1
f(1) -> 1
f(n) -> f(n - 1) + f(n - 2)

f :: Number -> Number
f(n where n < 2) -> 1
f(n) -> $:(n - 1) + $:(n - 2)

left side:
 constant <=> (a) -> a == constant
 n where p(n) <=> (a) -> p(a)

f(left side)

function generatePattern(n) {
    f :: Number -> NUmber
    f(n + 1) -> n
}

f(n where n == 1)