#2980 "rectform" causes infinite recursion depending on variable name

[David Scherfgen]

The following code causes an infinite recursion:

e: log(e)$
rectform(e);

The following doesn't:

e: log(f)$
rectform(e);

g: sqrt(g)$
rectform(g);

See mailing list posting "Issue with "rectform" and function/lambda parameter that's named like a variable".

Robert Dodier:

realpart and imagpart cause the same error.

Tracing MEVAL shows that's it's being called over and over to evaluate
notequal(log(e), 0). A stack trace shows $RECTFORM eventually calls
MEQP-BY-CSIGN which calls $REALPART which eventually calls MEQP-BY-CSIGN
again and the cycle continues.

I believe this is a bug in the predicate evaluation code -- MEVALP1
calls MEVAL.

[Rupert Swarbrick]

This should be fixed with [ca5af3] which I just pushed. I think that MEQP-BY-CSIGN recurses through $REALPART on purpose. Unfortunately, this particular (self-referential) example means that's a bit disastrous. So I've pushed a patch that catches recursions that look like they're going to diverge ("Hey, I've been here with this argument before...").