This lab is also available in PDF.
Summary: In this laboratory, we explore file creation,
input, and output in Scheme.
Contents:
a. Scan through this lab to determine what kinds of tasks you'll
need to complete.
b. You should also scan through
the reading on files in Scheme.
c. Start DrScheme.
As you may recall from the reading, I have prepared two simple files
for simple exploration of input and output,
/home/rebelsky/Web/Courses/CS151/2007S/Examples/hi.dat, and
/home/rebelsky/Web/Courses/CS151/2007S/Examples/sample.dat.
a. Using a sequence of commands in the interaction window,
read all the characters from hi.dat. For example,
> (define source
(open-input-file "/home/rebelsky/Web/Courses/CS151/2007S/Examples/hi.dat"))
> (read-char source)
#\H
...
> (read-char source)
#<eof>
> (close-input-port source)
b. Using a sequence of commands in the interaction window,
read all the characters from sample.dat.
c. Using a sequence of commands in the interaction window,
read all the values from sample.dat (use read rather than read-char).
d. Using a sequence of commands in the interaction window,
read all the values from hi.dat.
The file /home/rebelsky/Web/Courses/CS151/2007S/Examples/numbers.dat
contains five hundred and twenty-eight natural numbers.
a. Use sum-of-file from the reading to determine their sum.
b. How would you quickly determine if your attempt to sum those numbers was
correct?
Note: That file was copied from a similar file produced by Mr. Stone.
Using sum-of-file (and its helpers) as a pattern,
write a Scheme procedure file-size that takes as argument a
string that names a file and returns the number of characters in that file
(that is, the number of times that read-char can be called to
read a character from the file without returning the end-of-file object).
Find out what happens if sum-of-file or file-size
is given a string that does not name any existing file.
Write a procedure, read-lines, that takes the name of a
file as a parameter and returns a list of all the lines of the file
(with each line represented as a string). You can certainly use the
read-line procedure from the reading as a helper for
read-lines. You
might use sum-of-file as a pattern for
read-lines.
Write a procedure, display-file, that takes the name of
a file as a parameter and displays the contents of the file with each
line preceded by its line number. You may find it useful to call
upon the previous procedure to do the reading.
a. In the interactions pane, write a series of expressions that will
create a file, my-info, with the following lines
(substituting your own name and major).
Name: last, first
Major: major-or-undeclared
b. Write a Scheme procedure, (dump-info file-name last-name first-name major) that, given four strings as parameters,
writes the following to the file named by file-name,
Name: last-name, first-name
Major: major
Use the store-divisors procedure from the reading to
draw up a list of the divisors of 120, storing them in a file named
divisors-of-120. Examine the file afterwards and confirm
that the answer is correct.
By the way, don't give this procedure an extremely large number as
argument -- it's much too slow. There are more efficient ways to find divisors!
The Scheme standard says that if you try to open an output port to a
file that already exists, the effect is unspecified
, i.e., anything
might happen. Hence, designers of a particular implementation of Scheme
are free to do what they choose.
a. Find out through experimentation what DrScheme does in this situation.
b. Find out using DrScheme's Help Desk what DrScheme allows programmers
to do in this situation. (The help desk document is entitled
Opening file ports.)
Write a Scheme procedure that takes as arguments two file names (an
input file and an output file), counts the number of occurrences of
each vowel in the input file, and writes the result to the output file.
Note that the output file should have the following form (with numbers
in place of the number signs):
a: ###
e: ###
i: ###
o: ###
u: ###
If you have time or inclination, extend your procedure to deal with
all 127 ASCII characters.
;
