Description
Programming Languages
Homework 4
In this Homework assignment, we will be writing in LIS P. If you need help on how to run LISP on Openlab, refer to this document her e.
In writing the following LISP functions, you may use only these primitive functions:
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defun cond cons car cdr operators +, -, <, and >
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null eq
listp
atom symbolp
1. [8 ] Define a function my-length that takes one parameter, a list L, and returns the number of top-level elements in L. Examples:
○ (my-length nil) –> 0
○ (my-length ‘(b (a b c)) –> 2
○ (my-length ‘(a (((b))) c)) –> 3
○ (my-length ‘(a b c)) –> 3
2. Define a function my-memq that takes two parameters, a symbol A and a list of symbols L, and returns the list starting where the symbol bound to A was found. It returns nil otherwise. Examples:
○ (my-memq ‘a nil) –> nil
○ (my-memq ‘b ‘(a b c)) –> (b c)
○ (my-memq ‘d ‘(a b c d e f g)) –> (d e f g)
○ (my-memq ‘d ‘(a b c d)) –> (d)
○ (my-memq ‘d ‘(a b c)) –> nil
3. Define a function my-append that takes two parameters, a list L1 and a list L2, and returns the result of appending the two lists together. You must not call append.
○ (my-append ‘(a b c) ‘(d e f))
–> (a b c d e f)
○ (my-append ‘((a) (b) (c)) ‘((d) (e) (f)))
–> ((a) (b) (c) (d) (e) (f))
○ (my-append nil ‘(d e f))
–> (d e f)
○ (my-append ‘(a b c) nil)
–> (a b c)
4. Define the function my-attach which takes an object O and a list L and returns the list L with O added to the end. Examples:
○ (my-attach ‘a nil) –> (a)
○ (my-attach ‘d ‘(a b c)) –> (a b c d)
○ (my-attach ‘(a) ‘(b c)) –> (b c (a))
5.Define the function my-assoc that takes an atom A and a list L and returns the association pair for A. L is of the form ((key1 . value1)(key2 . value2) … (keyn . valuen)) Examples:
○ (my-assoc ‘a nil) –> nil
○ (my-assoc ‘a ‘((a . b)(c e f)(b))) –> (a . b) ○ (my-assoc ‘c ‘((a . b)(c e f)(b))) –> (c e f)
○ (my-assoc ‘b ‘((a . b)(c e f)(b))) –> (b)
○ (my-assoc ‘f ‘((a . b)(c e f)(b))) –> nil
6. Define the function freq that takes a symbol A and a list L and counts the occurrence of symbol A found anywhere in L. Examples:
○ (freq ‘c ‘((a c) c e)) –> 2 ○ (freq ‘f ‘(((s) o ) d)) –> 0
○ (freq ‘f ‘(((f) f) f f)) –> 4
7. Define the function mapping that takes 2 arguments – a list L, and an integer value val. Every element of the list L is a list of two atoms – key and object. (e.g. L <– ((35 kim) (67 clinton) (45 emma))) The function returns a list of objects whose key is less than val. Examples:
○ (mapping ‘((35 kim) (67 clinton) (45 emma)) 40) –> (kim)
○ (mapping ‘((24 a) (15 b) (56 c) (19 d)) 26) –> (a b d)
○ (mapping ‘((90 a) (80 b) (70 c)) 40)
–> nil
8.Define a function my-last that takes two parameters, a symbol A and a list of symbols L, and returns the list starting where the last occurrence of symbol A is in L. It returns nil only if A is not in the list. Examples:
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(my-last ‘a ‘(a b c a b c a b c d e f g))
–> (a b c d e f g)
○
(my-last ‘b ‘(a b c a b c a b c d e f g))
–> (b c d e f g)
○
(my-last ‘c ‘(a b c a b c a b c d e f g))
–> (c d e f g)
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(my-last ‘g ‘(a b c a b c a b c d e f g))
–> (g)
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(my-last ‘h ‘(a b c a b c a b c d e f g))
–> nil
9. Define the function my-reverse that takes a list L and returns the reverse of L. Examples:
○ (my-reverse nil) –> nil
○ (my-reverse ‘(a)) –> (a)
○ (my-reverse ‘(1 2 3 4 5)) –> (5 4 3 2 1)
○ (my-reverse ‘((1 2 3) 4 ((5 6)))) –> (((5 6)) 4 (1 2 3))
10.Define the function is-pattern? that takes two SIMPLE lists pat and str and returns the sublist of str which starts with the pat if pat is a substring of str. Otherwise, it returns nil. Examples:
○ (is-pattern? ‘(a b s) ‘(c d b a s))
–> nil
○ (is-pattern? ‘(c a c) ‘(b a j a c a c t u s))
–> (c a c t u s)
○ (is-pattern? nil ‘(a n y l i s t))
–> nil
○ (is-pattern? ‘(l i s p) nil)
–> nil
11.Define the function first-atom that takes a list L and returns the first atom of L. Examples:
○ (first-atom nil) –> nil
○ (first-atom ‘((2 (1) 4) 6)) –> 2 ○ (first-atom ‘((((s)) o ))) –> s
○ (first-atom ‘(1 (((2)) 3 4))) –> 1
12.Define a function find-all that takes a symbol A and a list L and finds and returns the first symbol following each occurrence of A in L, or nil if A does not occur in L. Note that A may occur nested within L, possibly as the last element of a sublist. You may assume that there is always a symbol occurring afterwards. Examples:
○ (find-all ‘a nil) –> nil
○ (find-all ‘a ‘(b a c a e)) –> (c e) ○ (find-all ‘a ‘(b d c e)) –> nil
○ (find-all ‘a ‘(b (a a) c)) –> (a c)
○ (find-all ‘a ‘((b a) ((c a b)))) –> (c b)
