From 8ffbc2df0fde83082610149d24e594c1cd879f4a Mon Sep 17 00:00:00 2001
From: Bryan Newbold <bnewbold@robocracy.org>
Date: Mon, 20 Feb 2017 00:05:25 -0800
Subject: Import Upstream version 2a6

---
 tree.scm | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 tree.scm

(limited to 'tree.scm')

diff --git a/tree.scm b/tree.scm
new file mode 100644
index 0000000..f400d1b
--- /dev/null
+++ b/tree.scm
@@ -0,0 +1,62 @@
+;;"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.
+
+;; Deep copy of the tree -- new one has all new pairs.  (Called
+;; tree-copy in Dybvig.)
+(define (tree:copy-tree tree)
+  (if (pair? tree)
+      (cons (tree:copy-tree (car tree))
+	    (tree:copy-tree (cdr tree)))
+      tree))
+
+;; 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))))
+
+;; 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))))
+
+(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))))
+
+(define copy-tree tree:copy-tree)
+(define subst tree:subst)
+(define substq tree:substq)
+(define substv tree:substv)
-- 
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