arithmetic.peg

additive <- multitive "+" additive / multitive `
case Node of
  Int when is_integer(Int) -> Int;
  [A, "+", B] -> A + B
end
`;
multitive <- primary "*" Mul:multitive / primary `
case Node of
  Int when is_integer(Int) -> Int;
  [A,"*",{'Mul',B}] -> A * B
end
`;
primary <- par:("(" add:additive ")") / dec:Decimal `
case Node of
  {dec,Int} when is_integer(Int) -> Int;
  {par,List} -> proplists:get_value(add,List)
end
`;
Decimal <- [0-9]+ `list_to_integer(Node)`;

rebar

rebar_test.app

{application, rebar_test,
 [
  {description, ""},
  {vsn, "1"},
  {modules, [
             arithmetic
            ]},
  {registered, []},
  {applications, [
                  kernel,
                  stdlib
                 ]},
  {mod, { myapp_app, []}},
  {env, []}
 ]}.