How not to bash the simplifier

I want to add features to %if but could not.  I came up with iif() instead.  iif has a different simplifier that %if.


load("simplifying.lisp");

simpiif(__cnd, __a, __b):=
block(
 [prederror:false],
 if is(__cnd)=true then
  __a
 elseif is(__cnd)=false then
  __b
 else
  /*  simp_assuming does not work right here for some reason, it leaves facts on the facts list without removing them 
all.  Don't know why. */
  simpfuncall('iif, __cnd, assuming(__a, __cnd), assuming(__b, not __cnd))
)$

simplifying(iif, simpiif);

but if I want to add this to existing simplifier for %if but I get an error.

load("simplifying.lisp"),
simpif(__cnd, __a, __b):=
block(
 [prederror:false],
 if is(__cnd)=true then
  __a
 elseif is(__cnd)=false then
  __b
 else
  /*  simp_assuming does not work right here for some reason, it leaves facts on the facts list without removing them 
all.  Don't know why. */
  simpfuncall('iif, __cnd, assuming(__a, __cnd), assuming(__b, not __cnd))
)$

simplifying(%if, simpif);
Warning: simpif is overriding built-in simplifier for %if

Is there any plans to add this simplification to %if?

Rich