foo 1, foo(2), 3, bar(4, foo(bar, 5), 6);
----
foo, bar # @_ # [ 2 ], [ ], [ 5 ], [ 4, 5, 6 ], [ 1, 2, 3, 4, 5, 6 ] # foo, bar, foo, bar, foo
foo 1, foo(2), 3, bar(4, foo(bar, 5), 6);
----
foo, bar # @_ # [ 2 ], [ ], [ 5 ], [ 4, 5, 6 ], [ 1, 2, 3, 4, 5, 6 ] # foo, bar, foo, bar, foo