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-rw-r--r--tree.scm53
1 files changed, 14 insertions, 39 deletions
diff --git a/tree.scm b/tree.scm
index f400d1b..e9bc999 100644
--- a/tree.scm
+++ b/tree.scm
@@ -1,21 +1,7 @@
;;"tree.scm" Implementation of COMMON LISP tree functions for Scheme
-; Copyright 1993, 1994 David Love (d.love@dl.ac.uk)
-;
-;Permission to copy this software, to redistribute it, and to use it
-;for any purpose is granted, subject to the following restrictions and
-;understandings.
-;
-;1. Any copy made of this software must include this copyright notice
-;in full.
-;
-;2. I have made no warrantee or representation that the operation of
-;this software will be error-free, and I am under no obligation to
-;provide any services, by way of maintenance, update, or otherwise.
-;
-;3. In conjunction with products arising from the use of this
-;material, there shall be no use of my name in any advertising,
-;promotional, or sales literature without prior written consent in
-;each case.
+;;; Author: Aubrey Jaffer
+;;;
+;;; This code is in the public domain.
;; Deep copy of the tree -- new one has all new pairs. (Called
;; tree-copy in Dybvig.)
@@ -27,34 +13,23 @@
;; Substitute occurrences of old equal? to new in tree.
;; Similar to tree walks in SICP without the internal define.
-(define (tree:subst new old tree)
- (let walk ((tree tree))
- (cond ((equal? old tree)
- new)
- ((pair? tree)
- (cons (walk (car tree))
- (walk (cdr tree))))
- (else tree))))
+(define (tree:subst new old tree . equ?)
+ (set! equ? (if (null? equ?) equal? (car equ?)))
+ (letrec ((walk (lambda (tree)
+ (cond ((equ? old tree) new)
+ ((pair? tree)
+ (cons (walk (car tree))
+ (walk (cdr tree))))
+ (else tree)))))
+ (walk tree)))
;; The next 2 aren't in CL. (Names from Dybvig)
(define (tree:substq new old tree)
- (let walk ((tree tree))
- (cond ((eq? old tree)
- new)
- ((pair? tree)
- (cons (walk (car tree))
- (walk (cdr tree))))
- (else tree))))
+ (tree:subst new old tree eq?))
(define (tree:substv new old tree)
- (let walk ((tree tree))
- (cond ((eqv? old tree)
- new)
- ((pair? tree)
- (cons (walk (car tree))
- (walk (cdr tree))))
- (else tree))))
+ (tree:subst new old tree eqv?))
(define copy-tree tree:copy-tree)
(define subst tree:subst)