Questions

• Questions about Assignment 1?
• Questions about Quiz 1?

Setup

• make a directory labs/L06 inside your ~/cs2613 git repository
• All of your work from today should be committed in that directory (and pushed before you leave).

Structural recursion on two parameters

• Form a group of 2 or 3.

• Work together to design the template in FICS Exercise 17

• Individually implement the function keep-first which follows this template.

• Compare your functions. Are there any interesting differences?

• Here is a test case

    (check-expect (keep-first (list 1 2 3 4) 3) (list 1 2 3))
  

• If that isn't enough for complete coverage for your solutions, add additional test cases.

Intersection of two ordered lists

Recall the template for structural recursion on two lists

(define (my-list-fn lst1 lst2)
  (cond
    [(empty? lst1) ... lst2 ...]
    [(empty? lst2) ... lst1 ...]
    [(cons? lst1)
        ... (first lst1) ... (first lst2) ...
        ... (my-list-fn (rest lst1) lst2) ...
        ... (my-list-fn lst1 (rest lst2)) ...
        ... (my-list-fn (rest lst1) (rest lst2)) ...]))

Use this template to complete FICS Exercise 20 You may find it helpful to refer to the function o-union defined in Section 5.4. Note that the fact that the lists are sorted is key an efficient solution here; you do not have to check that property.

Here are some test cases for the function intersection

(check-expect (intersection (list 1 2 3 4 5) (list 2 4 6 7))
              (list 2 4))

(check-expect (intersection (list 2 4 11) (list 1 2 3 4 5))
              (list 2 4))

Generating all subsets of fixed size

Start with the template from the first exercise and complete FICS Exercise 24. If your template needs updating, compare with cases in the two list template.

Use the built-in function append and the function cons-all you wrote in Lab 5.

Here are some test cases to illustrate the use of the function comb

(check-expect (comb '(a) 1) '((a)))
(check-expect (comb '(1 2) 1) '((1) (2)))
(check-expect (comb '(1 2 3) 2) '((1 2) (1 3) (2 3)))

Before next lab