Re: Straight From the Trenches Nooby Stumper Dunk the Kenny Gotta Be A Shorter Cleaner Way #26

On Jan 16, 7:12 pm, Pascal Costanza <p...@xxxxxxxxx> wrote:

(defun excise-ranges-helper (vector ranges)
   (declare (vector vector))
   (loop with nada = vector ;; ;)
         for (lower upper) in ranges
         do (fill vector nada :start lower :end (1+ upper))
         finally (return (loop for entry across vector
                               unless (eq entry nada)
                               collect entry))))

(defgeneric excise-ranges (sequence ranges)
   (:method ((sequence vector) ranges)
    (coerce (excise-ranges-helper (copy-seq sequence) ranges) 'vector))
   (:method ((sequence list) ranges)
    (excise-ranges-helper (coerce sequence 'vector) ranges)))


That's a good approach, but there are some unnecessary complications
here. I would write the following:

(defun excise-ranges (sequence ranges)
(loop with nada = (load-time-value (cons nil nil))
for (lower upper) in ranges
do (fill sequence nada :start lower :end (1+ upper))
finally (return (remove nada sequence :test #'eq))))

Note that I use a "private" cons, which is guaranteed not to be an
element
of the sequence at function entry or exit. Note that the sequence is
passed
just to FILL and REMOVE, which are generic sequence operators - no
need
to coerce anything.

Ariel
.

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