CS 22
Clab 10: map and filter
First, do exercises 2.30, 2.31, 2.32 on pages 112-113. You can
find them by scrolling down a couple of screens from:
http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-15.html#%_sec_2.2.2
If necessary review the material on pages 105 and 112. Remember to
substitute '() for nil wherever the text uses nil or put
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(define nil '())
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in your definitions window.
Here is the procedure filter from page 115 of the text.
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(define filter
(lambda (pred? l)
(cond
((null? l) '())
((pred? (car l)) (cons (car l) (filter pred? (cdr l))))
(else (filter pred? (cdr l))))))
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Use filter to define a procedure remove-neg that given an input
list of integers, returns a list of all the non-negative
integers in the input list.
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> (remove-neg '(1 -3 4 5 -6 -7))
(1 4 5)
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Now a challange
Finish the 8-queens problem, ex 2.42 page 124-126.
You can find
it by scrolling up a couple of screens from:
http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-15.html#%_sec_2.2.4
Solutions for Clab9 functions.
Here is some code for deep versions of subst and remove-all:
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;; subst* returns a list that substitutes new for old in an arbitrary
;; list, l, of symbols:
(define subst*
(lambda (old new l)
(cond
((null? l) '())
((list? (car l))
(cons (subst* old new (car l)) (subst* old new (cdr l))))
((eq? (car l) old) (cons new (subst* old new (cdr l))))
(else (cons (car l) (subst* old new (cdr l)))))))
;; remove-all* removes all occurrences of sym from an arbitrarily
;; nested list:
(define remove-all*
(lambda (sym l)
(cond
((null? l) '())
((list? (car l))
(cons (remove-all* sym (car l)) (remove-all* sym (cdr l))))
((eq? (car l) sym) (remove-all* sym (cdr l)))
(else (cons (car l) (remove-all* sym (cdr l)))))))
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If you have any questions from last clab,
begin with it and get your questions answered.
ask any questions you may have.
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