What to hand in, and how to hand it in

• Make a directory ~/cs2613/assignments/A2 (i.e. in your git repo for this class). All files related to this assignment should be saved in that directory.
• Make sure you commit and push all your work using git before 16:30 on Thursday October 16.

Marking

• This assignment will be worth 2% of your final grade.
• For a marking scheme, see racket-assignment

Questions

This assignment is based on FICS exercise 31, and the material in Lab 6 .

Follow the the rules of the FICS exercices 30, 31. In particular your solution(s) should not use explicit recursion or helper functions. You can (and should) use lambda. For full marks you should not use any builtins other than

• define, check-expect
• map, foldr
• lambda
• if, cond, not
• cons, empty, list

Flatten

Write a function flatten that removes one layer of list structure from the input. In particular your function should pass the following tests.

(check-expect (flatten empty) empty)
(check-expect (flatten '(() ())) empty)
(check-expect (flatten'((a) (b))) '(a b))
(check-expect (flatten'(((a 1) (b 1)) ((c 2) (d 2) )))
              '((a 1) (b 1) (c 2) (d 2)))

Cross

Write the function cross described in FICS exercice 31. While helper functions are not permitted for this exercise, you can re-use the body of flatten in your cross function if you want. You may find it helpful to debug with a version using flatten as a helper function, and then inline the flatten body before you hand it in.

Your function should pass the following tests.

(check-expect (cross '(a)'(1)) '((a 1)))
(check-expect (cross'(a b c)
                    '(1 2))'((a 1) (a 2) (b 1) (b 2) (c 1) (c 2)))

Tests

Make sure that both of your functions are tested adequately. See for what counts as “adequately”.