def add(x, y)
{
  return x + y;
}

assert_equal(2, add.get_arity());

auto b = bind(add, 2, _);

assert_equal(1, b.get_arity());

auto c = bind(b, 3);

assert_equal(0, c.get_arity());

assert_equal(6, b(4));
assert_equal(5, c());

def concat2(a,b,c,d)
{
  return to_string(a) + to_string(b) + to_string(c) + to_string(d);
}

auto d = bind(concat2, _, " Hello ", _, " World");
assert_equal(2, d.get_arity());

assert_equal("1 Hello 3 World", d(1,3));

auto e = bind(`<`, _, 5);
auto types = e.get_param_types();
assert_equal(2, types.size());
assert_equal(true, types[0].bare_equal(bool_type));