;;; -*-lisp-*-
;;;
;;; $Id$
;;;
;;; Collecting things into lists
;;;
;;; (c) 2005 Straylight/Edgeware
;;;

;;;----- Licensing notice ---------------------------------------------------
;;;
;;; This program is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 2 of the License, or
;;; (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program; if not, write to the Free Software Foundation,
;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

(defpackage #:collect
  (:use #:common-lisp #:mdw.base)
  (:export #:make-collector #:collected
	   #:collecting #:with-collection
	   #:collect #:collect-tail
	   #:collect-append #:collect-nconc))
(in-package collect)

(eval-when (:compile-toplevel :load-toplevel)
  (defvar *collecting-anon-list-name* (gensym)
    "The default name for anonymous `collecting' lists."))

(defun make-collector (&optional list)
  "Return a new collector object whose initial contents is LIST.  Note that
   LIST will be destroyed if anything else is collected."
  (let ((head (cons nil list)))
    (setf (car head) (if list (last list) head))))

(defmacro collected (&optional (name *collecting-anon-list-name*))
  "Return the current list collected into the collector NAME (or
   *collecting-anon-list-name* by default)."
  `(the list (cdr ,name)))

(defmacro collecting (vars &body body)
  "Collect items into lists.  The VARS are a list of collection variables --
   their values are unspecified, except that they may be passed to `collect'
   and `collect-tail' If VARS is empty then *collecting-anon-list-name* is
   used.  VARS may be an atom instead of a singleton list.  The form produces
   multiple values, one for each list constructed."
  (cond ((null vars) (setf vars (list *collecting-anon-list-name*)))
	((atom vars) (setf vars (list vars))))
  `(let ,(mapcar (lambda (v) `(,v (make-collector))) vars)
     ,@body
     (values ,@(mapcar (lambda (v) `(collected ,v)) vars))))

(defmacro with-collection (vars collection &body body)
  "Collect items into lists VARS according to the form COLLECTION; then
   evaluate BODY with VARS bound to those lists."
  `(multiple-value-bind
   ,(listify vars)
       (collecting ,vars ,collection)
     ,@body))

(defmacro collect (x &optional (name *collecting-anon-list-name*))
  "Add item X to the `collecting' list NAME (or *collecting-anon-list-name*
   by default)."
  (with-gensyms new
    `(let ((,new (cons ,x nil)))
       (setf (cdar ,name) ,new)
       (setf (car ,name) ,new))))

(defmacro collect-tail (x &optional (name *collecting-anon-list-name*))
  "Make item X be the tail of `collecting' list NAME (or
   *collecting-anon-list-name* by default).  It is an error to continue
   trying to add stuff to the list."
  `(progn
     (setf (cdar ,name) ,x)
     (setf (car ,name) nil)))

(defmacro collect-append (list &optional (name *collecting-anon-list-name*))
  "Append LIST to the tail of `collecting' list NAME.  This obviously
   involves copying LIST."
  (with-gensyms item
    `(dolist (,item ,list)
       (collect ,item ,name))))

(defmacro collect-nconc (list &optional (name *collecting-anon-list-name*))
  "Attach LIST to the tail of `collecting' list NAME.  This will involve
   destroying LIST if anything else gets collected afterwards."
  (let*/gensyms list
    `(when ,list
       (setf (cdar ,name) ,list)
       (setf (car ,name) (last ,list)))))

;;;----- That's all, folks --------------------------------------------------