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)