[alexandria-devel] A clean-room implementation of FILTER-IF from Paul Graham's "On Lisp."

Good day,

perhaps the function below meets the Alexandria's standards for conservativeness/usefulness:

(defun filter-if (fn &rest sequences) (labels ((iterate (acc sequences) (if (notany #'null sequences) (iterate (if-let ((testval (apply fn (mapcar #'car sequences)))) (cons testval acc) acc) (mapcar #'cdr sequences)) acc))) (nreverse (iterate nil sequences))))

The idea, but not the implementation, was taken from Paul Graham's book "On Lisp".

Also, i cannot come up with a good docstring, so such one would be appreciated.

regards, Samium Gromoff