Those are great ideas, and with any kind of /decent/ parser and code generator would be possible (because presumably the function expression returns a function

Those are great ideas, and with any kind of /decent/ parser and code generator would be possible (because presumably the function expression returns a function type, which can be stored in a variable or passed around). But this is in PHP, were is_* functions ONLY work on "expressions" that look like variables (not expressions that evaluate to values), and debug_backtrace, while it returns an array, can not be indexed inline without assigning the result of it to a variable first.