[plt-scheme] Reloading code

Hi all.  I'm very new to scheme so I'm sure I'll have a number of
questions.  I'll try to phrase them intelligently and clearly.

What I'm trying to do is create a program that is basically an event
loop.  It will read in various modules and then start the loop, the loop
will perform various processing tasks and look for user input, without
any input it will run various tasks again and look for input...etc.

What I need is for a user to input a command and have the program reload
parts of the program code, not necessarily all of it.  Probably
individual modules.   I don't know if it would be possible for an
internal command to reload individual procedures.  Purpose being if/when
a source file is modified on disk, I want the user (who won't have
access to the machine shell) to be able to reload just the modified
portion of the code.  Or as small a section as possible that includes
the modified section, such as a module perhaps.

I know this is probably an extended topic to get answered by mail, so
what I'm asking the list for is your reference links that might be
pertinent...  Snippets, examples, modules, etc, that would show me
things like this. (Or any examples of reloading code at all).

Thanks. :)