Perhaps also worth considering for inspiration is "elsoc", a useful hack
that Emacs has had for arguments quick-reference.
"eldoc" does a transient display of the args to the innermost
function/form that point is in. This display appears in the ``echo
area'' of the frame (roughly, status bar at the bottom of the window),
so you can glance at it, but it doesn't get in your face while you're
looking at the code and typing.
http://www.gnu.org/software/emacs/manual/html_node/emacs/Lisp-Doc.html
http://www.emacswiki.org/emacs/ElDoc
I'm sure that DrRacket would do it not as a hack like "eldoc", but
instead use some info that Check Syntax has. :)
Neil V.
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