[racket] Block diagram drawing library

Has anyone written a node drawing library using racket drawing code?

I want to try out a visual programming paradigm that gives programmers a
set of primitive constraint nodes like those depicted here:
http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-22.html#%_sec_3.3.5and
allows them to construct networks of constraints by drawing connectors
between constraints. If someone has written something like this before, it
would save me some time figuring out how to do it myself.

-- 

Cheers,
Mark Watts
Department of Computer Science
University of Texas at Austin
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