;;どう書く？org 条件を満たす行を取り除く をcommonLispで

これは簡単。
あえてcl-pprecを使ってみた。

;;どう書く？org 条件を満たす行を取り除く
(require :asdf)
(asdf:oos 'asdf:load-op :cl-ppcre)

(defun remcomment(in out)
  (with-open-file 
   (is in :direction :input)
   (with-open-file
    (os out :direction :output :if-exists :supersede)
    (do ((line (read-line is nil nil)
           (read-line is nil nil)))
    ((eql line nil))
      (if (not (cl-ppcre:all-matches "^#" line))
      (format os "~A~%" line))))))

これだけじゃなんだから
with-open-fileのオプション

:direction
 :input
 :output
 :io

:if-exists
 :error
 :new-version
 :rename
 :rename-and-delete
 :overwrite
 :append
 :supersede
 nil

:if-does-not-exist
 :error
 :create
 nil