Lab 1 (Racket Introductory Lab)

CSCI 301
Lab 1 (Racket Introductory Lab)
25 Points Total
 This is an individual assignment. Work through the following lab.
 In this lab assignment, you will work experimentally with the DrRacket programming environment
and the DrRacket language.
 Keep in mind that in addition to this lab, there are Racket and Scheme resources linked in the
syllabus if you need help.
 Read the descriptions carefully and turn in the complete answers!
 When you are finished submit a copy of the document with your answers on Canvas.
Part 1: Getting started in DrRacket
1. Start up DrRacket, which is the programming environment that we’ll be using. If this is the first
time you're starting up DrRacket, you'll see a warning about no language being specified. You
can ignore it, and all will work; alternatively, you can go to the Languages menu for DrRacket,
select "Choose Language," and make sure the first option is selected, which says "Start your
program with #lang..."
2. You will see a pair of windows. The bottom window says "Welcome to DrRacket." That is the
interactions/execution window. This is where you can test statements to see what they will do.
Try it out - in the interactions window, type
(+ 3 5)
This should add 3 to 5. In Racket, + is a function. To call a function in Racket, you place the name
of the function first and then its arguments, separated by spaces, inside parentheses. This takes
a little getting used to! In most programming languages, function calls look something like this:
function_name(arg1, arg2, arg3)
In Racket, function calls look like this:
(function_name arg1 arg2 arg3)
Change your program in some way. For example, re-type it as
(- -3 7)
Experiment with hitting the Esc key followed by either the p or the n keys, which allow you to
move backwards and forwards through your command history.
3. To run a program in DrRacket, either (1) type it into the edit (upper) window and then press Run
(upper right), or type it into the interactions window and follow it with a new line (enter).
Part 2: Basic Racket Primitives
1. In the interactions window, enter the following
(car '(11 12 13 14))
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(car '(a b c d))
(cdr '(11 12 13 14))
(cdr '(a b c d))
(car (11 12 13 14))
(cdr (a b c d))
What do car and cdr do? That last line of the above should cause an error. Explain why the
single quote necessary and what it does.
Answer:


2. Write sequences of cars and cdrs that will pick the symbol 'x out of the following
expressions:
(x y z m)
(y x z m)
(y z m x)
((y)(x)(z)(m))
((y z) (m x))
Answer:


3. Execute the following statements. Write down the return value for each statement and explain
what each of the functions cons, append, and list does.
;; This is a comment, by the way!
(cons 3 '(1 2))
(cons '(1 5) '(2 3))
(list 3 '(1 2))
(list '(1 5) '(2 3))
(append '(1) '(2 3))
(append '(1 5) '(2 3))
(cons 'x '(1 2))
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(list 1 2 3 '(4 5))
(cons '1 '2 '3 '(4 5))
Answer:


4. Execute the following code. Write down the return value for each statement and explain what
each of the functions length, reverse and member does.
(length '(a b c))
(reverse '(a b c))
(member 'a '(a b c))
(member 'b '(a b c))
(member 'c '(a b c))
(member 'd '(a b c))
Answer:


Part 3: Saving your code
Entering your code interactively is fun, but not a good idea for creating large programs. A better way to
go is to write your code, save it, then run it. Here's how to do it.
1. Start typing in some Racket code in the definitions window at the top of the screen. Make sure
that the first line says:
#lang racket
Use any of the above examples that you wish. When finished, save your program by going to the
File menu, and choosing Save Definitions.
2. Run your program by clicking on the clicking on the Run button, or by using the combination
Ctrl-T.
You should generally use this approach for entering and running Racket code, but entering code
directly into the interactions window is good for testing out quick ideas.
Part 4: Conditionals
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Racket has a number of different predicates for testing equality.
1. Try this code:
(equal? '(hi there) '(hi there))
(eqv? '(hi there) '(hi there))
(= '(hi there) '(hi there)) ;; yes, this will give an error
(equal? '(hi there) '(bye now))
(eqv? '(hi there) '(bye now))
(equal? 3 3)
(eqv? 3 3)
(= 3 3)
(equal? 3 (+ 2 1))
(eqv? 3 (+ 2 1))
(= 3 (+ 2 1))
(equal? 3 3.0)
(eqv? 3 3.0)
(= 3 3.0)
(equal? 3 (/ 6 2))
(eqv? 3 (/ 6 2))
(= 3 (/ 6 2))
(equal? -1/2 -0.5)
(eqv? -1/2 -0.5)
(= -1/2 -0.5)
Write down the return value for each of the statement and explain the difference among
equal?, eqv?, and =.
Answer:


2. Enter the following code:
(if (equal? 8 3)
 9
 10)
Modify the condition following if to get a different value to return.
[Note that Racket pays no attention whatsoever to how you indent your code. The above
indenting is stylistically useful to see what the "if" function is doing.] For textual conventions in
Racket programming, refer to https://docs.racket-lang.org/style/Textual_Matters.html
3. Enter the following code:
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(cond ((equal? 16 3) (+ 3 8))
 ((equal? 16 8) 12)
 (else (* 6 3)))
Write the return value for the above code. If replace all of the 16's in the above code with 8,
what is the return value? What about replace the 16’s with 3? What does the cond function
do?
Answer:


Part 5: Defining functions
1. In a new file, enter in the following code, save it, then run it.
(lambda (x)
 (+ x 1))
What does Racket return? The lambda function is an anonymous function. In this case, you have
defined an anonymous function that takes a parameter x and adds 1 to it. Functions are also
called procedures.
Without parameter(s), the above function cannot do much. It can be used this way by given
arguments:
((lambda (x)
 (+ x 1)) 3)
Run this, and give the result.
2. Define named functions:
(define add-one
 (lambda (x)
 (+ x 1)))
Save this code to a file called “add-one.rkt”, run it, then type (add-one 5) in the interactions
window. The define statement created a pointer, called add-one, which points to the function
you just created. Run this, and give the result.
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Run the following, and give the result. Does it serve the same purpose as the previous one?
(define (add-one x)
 (+ x 1))
3. Add the following lines in the same file and run it. Given the result.
(define another-add-one add-one)
(another-add-one 5)
At the pointer level, what is happening here? Draw a picture in the answer box indicating what
is happening.
Answer:


4. You can declare "local" variables in Racket via the use of the let function. For example, try the
following code:
(define a 2);;binding a variable to a value
(define b 3)
(define c 4)
(define (strange x)
 (let ((a 1) (b 2))
 (+ x a b))))
After executing this code, what are the values of a, b, and c? What is the return value when you
make the call (strange 4)? Explain your answers.
Answer:


Useful Reference links:
 https://courses.cs.washington.edu/courses/cse341/12au/racket/basics.html
 https://docs.racket-lang.org/reference/index.html