"expensive" here means that I am nervous about this part of the code. :-)

I think this bit of code (together with unpacking of objects) are in the critical path.

Hmmm... to compile a single statement with one parameter shouldn't be much more than lex:ing a couple of strings and doing a jump in a parser's jump table, then mallocing a bit memory for the minimal parse tree and probably copying the parameter.

OK, my instinctive fear of eval might be wrong, here. (-: You can take the compiler from the old C programmer but you can never stop him doing premature optimizations? :-)