[rules-users] Can I reuse eval output?

Hi, I've learned the use of eval() is not efficient, but it cannot be avoided in many cases. However, using temporary variables I tried: when $tmp: eval(...) ($tmp == false) or (eval(...)) Then ... end The above doers not compile; is there an alternative to reduce the number of evals by reusing their output? Another question is, is tehre something wrong in the above definition from a declarative programming point of view? Thanks, Arjun