shell-writing (syntax hilighting) advice?

[Isaac Dupree]

I'm trying to write a shell-style thing (actually a wrapper around bash) 
that gives syntax highlighting for the line being edited, and also 
displays more info.  For example, if I type "for" and pause, the "for" 
could turn red because it'd be a syntax error, and also display some 
helpful info like:

$ for
for NAME [in WORDS ...]; do COMMANDS; done
for (( EXPR1 ; EXPR2 ; EXPR3 )) ; do COMMANDS ; done

I found out that Readline has an "event hook" that I could at least use 
to get code's control every time a character is typed (and at other 
intervals).  But is it safe/possible to just write colored characters 
over the uncolored ones?  (Haskeline, Readline, I don't really care what 
library I use, as long as I can do what I want without re-implementing a 
whole line editing system!)

Hmm, I think I'll stick to that "syntax hilighting" question for a 
start, rather than trying to ask everything at once.

-Isaac