"Generate Macro vs Generate Attributes"

Hi...having a bit of trouble with my old friend Generate Macro.  I'm trying to create a macro called "subSelector" that is used in Select Subprocess.  Here's what I try to do:

subSelector                                 if(missing(eval(%{loopAtt})),1,2)

[%{loopAtt} is macro of a Loop Attributes operator that this is inside of]

This does not work - I get an error saying that it is not able to evaluate eval(%{loopAtt}).  However if I do the exact same thing in Generate Attributes, I have no trouble.  Of course this is annoying - I need to generate the attribute, Extract Macro, and then get rid of the attribute.  Help?  I'm in this situation more than you would think.  And why does Select Subprocess not have more functionality like Branch?  I like Select Subprocess better because of its flexibility (more than one option) but this macro thing gets in the way.

Thanks.

Scott