gistfile1.cl

;;;; Emacs Lisp

(require 'cl)

(setf *opening-stream-buffers*
      (make-hash-table))

(defmacro with-default-values (binds &rest body)
  `(progn
     ,@(mapcar
	(lambda (bind)
	  `(unless ,(first bind)
	     (setf ,(first bind) ,(second bind))))
	binds)
     ,@body))

(defun open (filename &optional direction)
  (with-default-values
   ((direction :input))
   (let ((buf (create-file-buffer filename)))
     (when (eq direction :input)
       (with-current-buffer buf
	 (insert-file-contents filename)))
     (setf (gethash buf *opening-stream-buffers*) (list direction filename))
     buf)))

(defun close (buf)
  (when (eq (first (gethash buf *opening-stream-buffers*))
	    :output)
    (with-current-buffer buf
      (write-region
       (point-min) (point-max)
       (second (gethash buf *opening-stream-buffers*))))
    (kill-buffer buf)))

;; clause = (stream filename &optional direction)
(defmacro with-open-file (clause &rest body)
  (destructuring-bind
      (direction filename stream)
      (let ((tmp (reverse clause)))
	(if (= (length tmp) 2)
	    (cons :input tmp)
	  tmp))
    `(let ((,stream (open ,filename ,direction)))
       (prog1
	   (progn
	     ,@body)
	 (close ,stream)))))