Fundamentals of Computer Science 1 (CS151 2003S)
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In this lab, you will explore the basic operations for working with lists and symbolic values. You may want to refer to the corresponding reading as you work on this lab.
Procedures used in this lab:
append
,
car
,
cdr
,
cons
,
length
,
list
,
listref
, and
reverse
.
cons
operations
list
procedure
cdr
Start DrScheme.
a. Call the cons
procedure to create a list that has the number 1 as its first and only
element. The result of your call should be
(1)
.
b. Call the cons
procedure to create a list that has the symbols a
and
b
as its two elements. The result of your call should be
(a b)
.
cons
operationsa. Figure out (without using DrScheme) the result of the following expression.
(cons 'alpha (cons 'beta (cons 'gamma (cons 'delta null))))
b. Check your answer by asking DrScheme to evaluate this expression.
list
procedure
Call the procedure list
, supplying the numerals
17
and 43
as arguments. Describe the value
returned by the procedure.
a. How would you call the list
procedure to create a list
containing the symbols alpha
, beta
, and
gamma
, in that order?
b. Verify your answer by entering the code in DrScheme.
How would you invoke the list
procedure to create an
empty list?
Determine by experiment whether it is possible to create a list in which the same element occurs more than once.
cdr
a. What is the cdr
of a
oneelement list?
b. Verify your answer by experimentation.
It makes no sense to apply the car
and cdr
procedures to an empty list,
because there's no way to split off the first element
of a list
that has no elements. What happens if you try it anyway? Find out by
having DrScheme evaluate a deliberately incorrect procedure call.
a. Does it make sense to apply car
and cdr
to
values other than lists? Why or why not?
b. Determine what happens if you apply these procedures to symbolic values and numeric values.
a. Create the list (e)
.
b. Create the list (d (e))
.
c. Create the list (b c)
.
d. Create the list (a (b c) (d (e)))
. You may
use list
, cons
, or a combination of
the two.
Use Scheme to give the name Greekletters
to the list
constructed by the expression (list 'alpha 'beta (list 'gamma1
'gamma2) 'delta)
. Then call the
length
procedure to
confirm that it has four elements.
Determine the length of the empty list.
a. Create a list of length 5. I don't care what's in the list.
b. Check your answer by having Scheme compute the length of that list.
a. Create the list (a (b c) (d (e)))
b. What do you think the length of this list should be?
c. Experimentally determine the length of this list.
d. Explain the result.
Use Scheme to compute the reversal of the list whose elements are the
symbols senior
, junior
, sophomore
,
and freshling
, in that order.
a. If a list has another list as one of its elements, should
reverse
reverse
that inner list as well as the outer one?
b. Find out by experiment what Scheme does.
a. Use Scheme to find the result of stringing together (with append
) a list with the
symbols alpha
and beta
as its elements and a
list with the numbers 1, 2, and 3 as its elements.
b. How many elements does the resulting list have?
a. Invoke the procedure list
, applying it to the two
lists that you strung together in the previous exercise: a list with the
symbols alpha
and beta
as its elements and a
list with the numbers 1, 2, and 3 as its elements.
b. How many elements does the resulting list have?
c. The answer to this question is different from the answer to the question at the end of the previous exercise  why?
a. Write a call to the procedure cons
, applying it to our
favorite two lists: a list with the symbols alpha
and
beta
as its elements and a list with the numbers 1, 2, and
3 as its elements.
b. How many elements does the resulting list have?
c. Why is the answer to this question different from the answers to the questions at the end of the previous two exercises?
Write a call to the listref
procedure that
will extract the fourth element of the list
(38 72 apple 1/3 sample)
That is, you should extract the number 1/3.
Quit DrScheme and log out of the workstation.
If you have extra time,
(a (b c) (d (e)))
using cons
rather than quote or list
.
(a (b (c (d (e ())))))
using cons
.
The append
procedure
joins together the elements of a list to make a new list. Hence, when
you append two lists together, the total number of elements in the new
list is the sum of the number of elements in the lists.
The list
procedure
creates a new list whose elements are the parameters to list
. Hence, if list
takes two parameters, the
length of the result is always two, regardless of what those parameters
are.
The cons
procedure
builds a new list by placing its first parameter at the start of its
second parameter (which is a list). Hence, the length of the result is
one more than the length of the second parameter.
2 Septemer 1997 [John David Stone]
31 March 2000 [John David Stone]
http://www.cs.grinnell.edu/~stone/courses/scheme/spring2000/symbolsandlists.xhtml
.
Friday, 1 September 2000 [Samuel A. Rebelsky]
http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2000F/Labs/lists.html
.
Sunday, 28 January 2001 [Samuel A. Rebelsky]
Monday, 29 January 2001 [Samuel A. Rebelsky]
list
problem to handle
inclass questions.
http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2001S/Labs/lists.html
.
Friday, 6 September 2002 [Samuel A. Rebelsky]
http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2002F/Labs/lists.html
.
Wednesday, 22 January 2003 [Samuel A. Rebelsky]
Tuesday, 28 January 2003 [Samuel A. Rebelsky]
http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2003S/Labs/lists.html
.
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[SamR]
Disclaimer:
I usually create these pages on the fly
, which means that I rarely
proofread them and they may contain bad grammar and incorrect details.
It also means that I tend to update them regularly (see the history for
more details). Feel free to contact me with any suggestions for changes.
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.
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