CSC151.02 2015S, Class 23: Revisiting Lists =========================================== * Continue partners. * Food? (optional) * Fun with HW 5. _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * Quiz. * Lab. Preliminaries ------------- ### Admin * Review session Monday at 7:00 p.m. * One of your classmates passed along the following article which you might find interesting. * * Prospies Monday! Be prepared for special activities. * Friday PSA * In making choices this weekend, please make sure that Nobody Gets Hurt (including you). * There are a lot of illnesses going around campus. Rest will help you avoid them better than almost anything. (I'm telling myself the same thing.) ### Upcoming Work * [Homework 6](../assignments/assignment.06.html). Is optional. * Due Tuesday at 10:30 p.m. * Replaces lowest HW, provided it is higher than the lowest. * Exam 2 to be assigned on Tuesday. * No lab writeup for today. * Reading for Monday: Recursion Basics * [Recursion Basics](../readings/recursion-basics-reading.html) * A cool and different topic that we'll be talking about through spring break (and the rest of the semester). ### Extra Credit Opportunities #### Peer Support (Afternoon Section) * Indoor Track Today and Saturday. Support Grinnell Pride! * Belly Dancing 3:30-5:00 p.m. and Wednesday 7:00-8:00 p.m. ### Other Good Things * Neverland Players this weekend. * Spend thirty minutes going to the thing at Garander tonight at 10:00 p.m. * Stephen Hawking movie tonight 6pm and 9pm in Harris Cinema. * Today is last day of Amy Flores show in Smith. ### Questions ### Quiz! * When you finish, keep your paper by you. We will be by to pick it up. * When you finish, start GIMP and DrRacket and look over the lab, but wait for your partner. Lab --- * `cons` can build things that aren't lists. You only get a list if the second parameter is a list. * Scheme/Racket show you non-list pair structures by including a period somewhere (traditionally right before the end). * (cdr (cons a b)) is always b * (car (cons a b)) is always a * Lots of pronounciation: cadr, cddr, cadadr Learning Outcomes ----------------- * How to build and disamble lists with cons, car, and cdr. * We can use a list to represent a group of related information * The description of a drawing * The description of a class '('CSC 151 2 "Functional Problem Solving" 1) * If we know that representation, we can build procedures that construct things to match it or that deconstruct things to use them. HW5, Revisited -------------- * You have written `(image-sample image x-coordinates y-coordinates)`. * You could also have written `(image-sample image shape xs ys)`. * It's easy to generate long lists of xs and ys * `(map (lambda (i) (modulo (* i 11) (image-width image))) (iota 1000))` * `(map (lambda (i) (modulo (* i 13) (image-heightimage))) (iota 1000))` * Putting it all together, we can get some great pictures.