Bash Script Editing Mode?

[formido <formido@gmail.com>]

There's a shell mode, but it has a prompt and doesn't help you
incrementally create a shell script as efficiently as it could, unless
I'm missing something. Is there any shell script mode that works more
like the elisp, python, or erlang repls, where you can execute your
choice of several lines at once and you can go back and edit and
execute the lines in situ? If I write a bash function, editing and
reloading the function is a painful process. I'm looking for something
a little bit like the Mac's BBEdit shell worksheets (only better).

I considered altering the usual shell mode, but it would take more
than slight edits, so I'm hoping something's already out there. For
example, one should be able to go back to a function, tweak it, and
reload with a minimum of keyboard fuss.

Michael