I agree that functionally pure code could allow for amazing programmatic rewriting. Imagine coupling that with homoiconic syntax. Not necessarily to have Lisp-s

I agree that functionally pure code could allow for amazing programmatic rewriting. Imagine coupling that with homoiconic syntax. Not necessarily to have Lisp-style macros, but rather so you could offer repl-based programmatic rewriting/refactoring tools, where the tools know that your code is pure and thus can be "reasoned about mathematically."