#1721 defining infix operator leads to a crash

[Anonymous]

Maxima 5.18post http://maxima.sourceforge.net
Using Lisp Clozure Common Lisp Version 1.4-dev (WindowsX8632)

(%i1) infix("imp", 50, 50, clause, clause, clause)$
(%i2) "imp"(a, b):= not(a) or b$

OK:

(%i3) a and (b imp c);
(%o3) a and ((not b) or c)

Not OK: (Maxima terminates)

(%i4) (a and b) imp c;

[Nobody/Anonymous]

its the same with
(%i1) imp(a,b) := not(a) or b;
(%o1) not(a) or b
(%i2) imp(a and b, c);
*** - Program stack overflow. RESET ...

[Robert Dodier]

Looking at the stack trace, it appears Maxima is trying to
evaluate a and b, for which it first needs a, which is
bound to a and b, for which it first needs a, ... ad infinitum.

(Maxima has so-called dynamic binding, not lexical.
There are arguments either way, but for the moment let's
take it as a given.)

Just renaming the argument variables avoids this problem:

imp (aa, bb) := not(aa) or bb;
a and b imp c;
=> ((not a) or (not b)) or c

Of course a name collisions causes it to crash as before:

aa and bb imp c;
=> stack overflow

Not sure if there's anything to do here aside from trying
to work around the problem.