"Okay, now I get it. iif() is a function that only works for simplifying
functions. If you want to actually plug in a value for x inside an "if"
like this one. You will crash Maxima.
(1/(x-1) * if equal(x,1) then 1 else (x-1));
%,x=1;
results in an error
You could do
(1/(x-1) * if equal(x,1) then 1 else (x-1))$
somesimplifyercall(%);
-> if equal(x,1) then error("divide by zero") else 1"
Another thought. Doing it this way puts time bombs in the expression.