[stack] Function Level Programming

I am looking at the function level programming entry on Wikipeda (
http://en.wikipedia.org/wiki/Function-level_programming ) and I am
intrigued.

"This restriction means that functions in FP are a module (generated
by the built-in functions) over the algebra of functional forms, and
are thus algebraically tractable. For instance, the general question
of equality of two functions is equivalent to the halting problem, and
is undecidable, but equality of two functions in FP is just equality
in the algebra, and thus (Backus imagines) easier."

This sounds significant, but I don't know how to leverage such
information practically. What other kinds of things can you do if
functions are a module? Are functions a module in Joy?

Thanks,
Christopher