Type the following command at the terminal to copy the template file to the current directory (note the period at the end):
cp ~cs61as/autograder/templates/hw0-2.rkt .
Or you can download the template here.
If you are working on the lab computers, the grader command will run the autograder. If you are working on your own personal machine, you should download grader.rkt and the hw0-2-tests.
The expression (+ 8 2) has the value 10. It is a compound expression made up of three atoms. For this problem, write five other Racket expressions whose values are also 10:
Let's build some functions to deal with words and sentences. We'll give you the second procedure from the previous lab. You might also find the word function useful.
first-two that takes a word as its argument, returning a two-letter word containing the first two letters of the argument.two-first that takes two words as arguments, returning a two-letter word containing the first letters of the two arguments.two-first-sent that takes a two-word sentence as argument, returning a two-letter word containing the first letters of the two words.-> (first-two 'ambulatory)
'am
-> (two-first 'brian 'epstein)
'be
-> (two-first-sent '(brian epstein))
'be
Write a predicate teen? that returns #t if its argument is between 13 and 19, inclusive.
-> (teen? 19)
#t
-> (teen? (/ 39 2))
#f
Write a procedure indef-article that takes in a word as its only argument and returns a sentence. See examples below for how indef-article should work. Remember that the indefinite article for anything that starts with a consonant is "a", and the indefinite article for anything that starts with a vowel is "an". You can ignore any edge cases.
-> (indef-article 'beetle)
'(a beetle)
-> (indef-article 'apple)
'(an apple)
Write a procedure insert-and that takes a sentence of items and returns a new sentence with an and in the grammatically correct place.
-> (insert-and '(john bill wayne fred joey))
'(john bill wayne fred and joey)
Write a procedure query that turns a statement into a question by swapping
the first two words and adding a question mark to the end of the last word. You can ignore any edge cases.
-> (query '(you are experienced))
'(are you experienced?)
-> (query '(i should have known better))
'(should i have known better?)
-> (query '(you were there))
'(were you there?)
Write a procedure european-time to convert a time from American AM/PM
notation into European 24-hour notation. Also, write american-time, which
does the opposite.
-> (european-time '(8 am))
8
-> (european-time '(4 pm))
16
-> (european-time '(12 am))
0
-> (american-time 21)
'(9 pm)
-> (american-time 12)
'(12 pm)
Write a procedure describe-time that takes a number of seconds as its argument and returns a more useful description of that amount of time. Assume that there are 365.25 days in a year. You only need to account for time periods up to a day.
-> (describe-time 45)
'(45 seconds)
-> (describe-time 930)
'(15.5 minutes)
You may notice that Racket handles integer division a little strangely:
-> (/ 1 2)
1/2
You can force Racket to return numbers with decimal points (AKA floating-point numbers) by using decimal points in one or more of your arguments:
-> (/ 1.0 2)
0.5
The following program doesn't work. Why not? Fix it and explain why.
(define (superlative adjective word)
(se (word adjective 'est) word))
This is how superlative should work:
-> (superlative 'dumb 'exercise)
'(dumbest exercise)
For instructions, see this guide. It covers basic terminal commands and assignment submission.
If you have any trouble submitting, do not hesitate to ask a TA!