[pstricks] Adder for pst-circ

[Joel Salomon]

I'm trying to create a control-systems simulation diagram, for which
I'm trying to define an adder.  A simple version of what I want to
create looks like:
	\begin{pspicture}(2,2)
		\psline{->}(0,1)(0.5,1)
			\rput(.7,1){$+$}
		\psline{->}(1,2)(1,1.5)
			\rput(1,1.3){$+$}
		\psline{->}(1,0)(1,0.5)
			\rput(1,.7){$-$}
		\lamp(.5,1)(1.5,1){}
		\psline(1.5,1)(2,1)
	\end{pspicture}
Options this needs include the presence or absence of either or both
of the top and bottom nodes, and a +, -, or blank in any quadrant and,
by default, arrows pointing to quadrants that have a + or -.  This can
be a dipole, tripole, or quadrupole depending on how it's invoked.

I'd be glad to do the programming if someone tells me it can be done
and points me to a model.

--Joel