clipka wrote:

> You *can* write a macro this way:
> 
>   #macro myMacro(p1,p2)
>     #if (p2 > 0)
>       #declare this = sphere { p1, p2 }
>     #else
>       // nothing
>     #end
>   #end


You can also get rid of the reference to the global
variable name from within the macro by using the more
cumbersome:

#macro myMacro(p1,p2,outobjcreated,outobj)
   #if (p2 > 0)
     #local outobjcreated = true;
     #local outobj        = sphere { p1, p2 }
   #else
     #local outobjcreated = false;
   #end
#end

// Need to be initialized, value irrelevant
#declare myoutobjcreated = false;
#declare myoutobj        = false;

myMacro(<0,0,0>, -1, myoutobjcreated, myoutobj)

#if (myoutobjcreated)
   #debug "Object myoutobj is ready for use"
#else
   #debug "No object created"
#end


I'm still puzzling whether one could get rid of the myobjcreated
variable. I tried assigning "false" to myoutobj but I don't know
of any way to test whether a variable contains a float or an object,
and #if will raise an error if it is an object. I also tried
"#undeffing" outobj but that seems to only undef the local
variable name outobj, not the passed variable. Makes sense
in a general way but not so much with the output semantics
for variables passed to macro parameters: If I can change
the value of the passed variable, I should also be able
to reset it to some kind of null reference.

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