How 'often'? Either all the time or very rarely, depending on your perspective. You wouldn't have 50% of your codebase treating code as data, because only a few

How 'often'? Either all the time or very rarely, depending on your perspective. You wouldn't have 50% of your codebase treating code as data, because only a few lines of macros could define an entire new paradigm on top of what's included in common lisp. Those macros could be used pervasively throughout the codebase; they could be used often but written rarely.