From: John Feminella <johnf@...>
Date: 2011-02-10T21:01:31+09:00
Subject: Modifying the AST of a running Ruby script in-place

Is there a way to not merely _construct_ the AST of a Ruby script, but
also to _modify_ it in-memory, thus producing a different script? (I
realize that there's no Ruby spec and thus, every Ruby implementation
is going to have a different parse tree and thus a different answer.
My question is confined mostly to MRI.)

As a simple example, suppose that I would like to write a method
called "subtractify(m)". The subtractify method accepts another method
`m` as input, and then changes all uses of the `+` operator to `-`.
The result is a new, unbound method that can either replace the
original method or be attached somewhere else. If I were to bind this
new method to the original object and replace the original one
(similar to overwriting it with a new `def`), the result should be
equivalent to running the "subtractified" variant of the method with
the original object as the receiver.

Is that (or a similar situation) possible? If so, are there
limitations to what can and can't be modified?

~ jf
--
John Feminella
Principal Consultant, BitsBuilder
LI: http://www.linkedin.com/in/johnxf
SO: http://stackoverflow.com/users/75170/