[iterate-devel] thereis vs. collect ?

I'm getting an error when using thereis and collect in the same iterate:

(iter (for x :in '(3 1 4 1 5 9)) (thereis (evenp x)) (collect x)))

gives

Attempt to do COLLECT accumulation into a variable already being used for IF-EXISTS accumulation.

I don't really understand how these variables in collect, thereis, etc are chosen, maybe soemone could enlighten me.

I can rewrite it to bypass thereis:

(iter (for x :in '(3 1 4 1 5 9)) (let ((result (evenp x))) (when result (leave result))) (collect x)))

or use my own accumulation variable:

(iter (for x :in '(3 1 4 1 5 9)) (thereis x) (collect x :into y)))

but I prefer not to do either of those. Far too much typing!

Cheers, Chris Dean