;; guile-lib
;; Copyright (C) 2003,2004 Andy Wingo <wingo at pobox dot com>

;; 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, contact:
;;
;; Free Software Foundation           Voice:  +1-617-542-5942
;; 59 Temple Place - Suite 330        Fax:    +1-617-542-2652
;; Boston, MA  02111-1307,  USA       gnu@gnu.org

;;; Commentary:
;;
;;A nodal tree is a tree composed of nodes, each of which may have
;;children. Nodes are represented as alists. The only alist entry that
;;is specified is @code{children}, which must hold a list of child
;;nodes. Other entries are intentionally left unspecified, so as to
;;allow for extensibility.
;;
;;; Code:

(define-module (container nodal-tree)
  #:export (nodal-tree? make-node
            node-ref node-set! node-children))

;; Returns pairs, not lists
(define (group-pairs l)
  (let lp ((in l) (out '()))
    (cond
     ((null? in) (reverse! out))
     (else (lp (list-cdr-ref in 2) (acons (car in) (cadr in) out))))))

(define (make-node . attributes)
  (or (even? (length attributes)) (error "invalid node atrributes"))
  (cons 'nodal-tree
        (let ((body (group-pairs attributes)))
          (if (assq 'children body)
              body
              (acons 'children '() body)))))

(define (node-set! node name val)
  (set-cdr! node (assq-set! (cdr node) name val)))

(define (node-ref node name)
  (assq-ref (cdr node) name))

(define (node-children node)
  (or (node-ref node 'children) '()))

(define (nodal-tree? x)
  "Predicate to determine if @var{x} is a nodal tree. Not particularly
efficient: intended for debugging purposes."
  (and (list? x)
       (eq? (car x) 'nodal-tree)
       (and-map pair? x)
       (and-map nodal-tree? (node-children x))))
