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Preface
Part I
Chap 1
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Chap 3
XEmacs
Chap 4
Chap 5
Chap 6
Chap 7
Chap 8
Chap 9
Part II
Chap 10
Chap 11
Chap 12
Chap 13
Chap 14
Chap 15
Chap 16
Chap 17
Chap 18
Chap 19
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Chap 21
Chap 22
Chap 23
Part III
Chap 24
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Chap 30
Chap 31
Chap 32

CHAPTER 18: RECURSION ON TREES
 Corrections
 page 130, lines 1  7: Change indentation from
(defun bstreep (tree)
"A bstree is either an element, or a threemember list,
the first of which is an element."
(or (typep tree 'util:element)
(and (listp tree)
(= (length tree) 3)
(typep (first tree) 'util:element))))
to
(defun bstreep (tree)
"A bstree is either an element, or a threemember list,
the first of which is an element."
(or (typep tree 'util:element)
(and (listp tree)
(= (length tree) 3)
(typep (first tree) 'util:element))))
 Page 298, lines 15  18: Change
(defun lhs (rule)
"Returns the righthand side of the RULE."
(checktype rule rule)
(first rule))
to
(defun lhs (rule)
"Returns the lefthand side of the RULE."
(checktype rule rule)
(first rule))
 Notes

 Read Chapter 18.
 Do Exercise 18.1 if you are not already comfortable with the
difference between
eql and equal .
 Do Exercises 18.2 through 18.4 if you need to in order to
feel more comfortable with recursion on trees. In any case, note the
typecase function.
 Do Exercise 18.5. Try both
lisp:equal and
lisp:treeequal on trees at least one of whose leaves is
a string.
 For Exercise 18.6, explore the differences between
equal and equalp . I personally often use
equal , but seldom use equalp .
 For Exercise 18.7, look in Section B.13.4. The functions
that are not explicitly called destructive are not.
 Do Exercises 18.8  18.11 for your own understanding.
 Don't bother doing Exercises 18.12  18.22.
 Do Exercises 18.23 and 18.24. Submit a file named
ch18.cl with flatten and
flatten2 defined in the ch18 package.
 Do Exercises 18.25  18.27. Submit your updated match.cl file.
Please remember to revise the line "This file satisfies the exercises
through Exercise ???"
Exercise 18.25 is probably not worded as well as it might be.
You should rewrite match and substitute so
that in calls like (match pat tree) and (substitute
pat subs) , pat and
tree can be arbitrary trees, though only
pat can contain variables. That is, previously
match worked on two lists, one of which could contain
variables; now it should work on two trees, one of which can contain
variables. Remember that, whereas the base case of lists is
nil , the base case of trees is any atom.
Here are some examples of attempts to match trees:
> (match 'a 'a)
((T T))
> (match 'a 'b)
NIL
> (match '?x 'a)
((?X A) (T T))
> (match '(?x) 'a)
NIL
> (match '?x '(a))
((?X (A)) (T T))
> (match '(a ?x c) '(a b c))
((?X B) (T T))
> (match '(a (?x) c) '(a b c))
NIL
> (match '(a ?x c) '(a (b) c))
((?X (B)) (T T))
> (match '(a (?x) c) '(a (b) c))
((?X B) (T T))
 When you have submitted correct exercises through this
chapter, you will have earned a grade of C+ (above a 2.0).
