Homework 2
due Sep 22, 2008
The homework requires you to solve the following problems via scheme programming. You need
to develop your scheme programs using the DrScheme environment and submit your solution file
1. (15pts) Define a recursive function count which takes two parameters, an atomic value (a
symbol or a number) xand an arbitrary value y. The function returns the number of times
that xappears in y. Use the following test cases for your function.
> (count 3 7)
0
> (Check ’y ’y)
1
> (count ’x ’((x 3) (y 2) (3 z)))
1
> (count 3 ’((x 3) (y 2) (3 z)))
2
> (count ’z ’(x (z 5) (4 (z 4))))
2
> (count ’4 ’(x (z 4) (4 (z 4))))
3
2. (15pts) Define a recursive function Check which takes two parameters, an atomic value (a
symbol or a number) xand an arbitrary value y. The function finds the first occurrence of
xin yand returns the first component in ythat immediately contains x. If xis not in y, an
empty list is returned. Use the following test cases for your function.
> (Check 3.2 ’y)
empty
> (Check ’y ’y)
’y
> (Check ’x ’((x 3) (y 2) (3 z)))
(list ’x 3)
> (Check ’z ’(x (z 5) (4 (z 4))))
(list ’z 5)
1