You can use functions outside of shell scripts - they can serve as a better kind of alias, or as a way of modifying the current shell without having to type the '.' before the script.

Shells languages arguably should be usable programming languages. So start with a good, expressive one add add scripting as a library:

http://users.eecs.northwestern.edu/~jesse/pubs/caml-shcaml/

Incidentally, that would also dramatically decreased security and maintainability problems.