--- title: Eboard 04 Introducing lists number: 04 section: eboards held: 2017-09-01 --- CSC 151.01, Class 04: Introducing lists ======================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Topics: * Context: What and why lists? * Building lists * Mapping lists * Reducing lists * Sorting lists * Other list operations * Structure * Quiz * Lab * Debrief ### News / Etc. * New places/partners! * No attendance today. * Thank you to everyone who is pointing out broken links and mangled text! * Make sure to send writeups to your grader, not me. Also make sure to carbon copy your parter. ### Upcoming Work * [Writeup for class 3](../writeups/writeup03) due tonight at 10:30 p.m. * [Writeup for class 4](../writeups/writeup04) due Monday night at 10:30 p.m. * Exercise 5 * To: * Subject: CSC 151.01 Writeup 4 (YOUR NAMES) * Read: [Defining your own procedures](../readings/procedures) * Read: [How Scheme evaluates expressions, take 2](../readings/scheme-eval-2) * [Assignment 2](../assignments/assignment02) due Tuesday. ### Extra credit (Academic) * Rosenfield symposium, next week. (Lots of different events) * CS Table, Tuesday at noon: TBD. ### Extra credit (Peer) * Women's Soccer vs. Simpson, **TODAY**, 5:00 pm, Springer Field * Women's Soccer vs. Alumnae, Sunday, Noon, Springer Field * Men's Soccer vs. Coe, **TODAY**, 3:00 pm, Springer Field * Men's Soccer vs. Alumni, Sunday, 2:00 pm, Springer Field * Volleyball vs. Wisconsin-Whitewater, **TODAY**, 4:00 pm, Coe College (Cedar Rapids) * Volleyball vs. Wisconsin-La Crosse, **TODAY**, 8:00 pm, Coe College (Cedar Rapids) * Tiger Football. Tonight at 7pm ish. ### Extra Credit (Misc) * Community Hour (Dialogues Across Difference), Tuesday at 11 a.m. in JRC 209. * CLS Kick-Off Event, Tuesday at 11 a.m. in "North Campus Grove". ### Friday PSA * You are clearly awesome. I do not want you damaged. (Others don't want you damaged either.) * Think about what is right *for you*, in advance, and stick to it. * CONSENT IS ABSOLUTELY POSITIVELY NECESSARY. ### Questions I left Firefox open on another machine. What do I do? : Ask Sam or Marli to type some magic incantations. What locations are available for me to work on MathLAN machines? : 3813 and 3815. Classes in the rooms during the days, available at night. : CS Learning Center (3828, I think). All the time, except if there's a mentor sessions there. : 3819. (See 3813) : Math Lab, when it's open. : Science 2401. If we emailed the lab writeup to you by mistake (or because Sam's instructions were not clear enough), should we resend it to the grader? : Yes, please. How long should lab writeups be? : Enough to get the job done, but not much more. : Sam will send out an example. Can we take notes in DrRacket while we are working on labs? : Yes. Stuff preceded by a semicolon is a comment and is ignored by DrRacket. : So put notes in the definitions pane, add semicolons, and save to desktop (or somewhere else) Consider the following definitions: `(define one 1)`, `(define two 2)`, `(define three 3)`. If we type `(list one two three)`, we get `'(1 2 3)`. Why? And what about symbols? : What does `one` mean? There's a variable named `one` which contains (or references) (or names) the value 1. : When DrRacket sees something like `(list one two three)`, the first thing it does is looks up the variables in its table of values. : In contrast, `'one` means "the symbol one". : DrRacket is weird: `'1` means "the numeral 1" not "the symbol 1". Symbols must not look like numbers. `'` operation is a bit more complex than "make this a symbol". Procedure calls and lists look similar. Really? I see a quotation mark in front of lists, both when I type them in the "don't do it this way" approach and when DrRacket gives them back to me. : Some Scheme interpreters don't include the quotation mark, which can lead to confusion. That's why we mention it. The mentors are awesome, aren't they? : Yes. Quiz ---- * Ten minutes. * Questions * "Sift flour" means to put the flour in a mesh and to shake it back and forth in order to remove larger particles. **I make cultural assumptions. Ask me about it when I use terms that you don't understand. The failing is mine, not yours.** * Yes, you can use the back of the page. * When you finish, bring up the lab (if possible) and start reading through it until your partner is ready. * Once both partners are ready, start. * I will return graded quizzes on Monday. Lab --- Do [the first lists lab](../labs/simple-lists). Be prepared to debrief. Debrief ------- What's the writeup? : Exercise 5 I'm stumped as to how to add 1.5 to each element of a list. I could add 1 with `increment`, but I don't know a procedure that adds 1.5. : Right now, your tools are limited, so you have to think about how to use those tools. Your problem solving abilities grow when you problem solve with restricted tools. : Since we want to do an operation that involves two values (addition), you'll need to make a second list and then use `map`. How do I know when to include `csc151/lists`, `csc151/hop`, and `csc151/numbers`? : Just make it practice to do so. Wow. That's a lame answer. I really want to know what's defined in those files. : `csc151/lists` currently provides `iota`, `map1`, `reduce` (and variants), and possibly something else. : `csc151/hop` currently provides `o`, `section` (next class), and some other things we'll cover later in the semester. : `csc151/numbers` currently provides `increment` and `decrement`. Why do you keep typing those backticks? : It makes things format nicely when I turn this into a Web page. Can you help me think about the relationship between `map` and `reduce`? : You use `map` when you want to go from a list of values to another list of values. It's a cool mechanism for one form of repetition. We might, for example, add two to each element in a list. `(map (o increment increment) (list 1 2 3 4 5)) => ` : You use `reduce` when you have a bunch of values that you want to combine into a single value. It's a cool mechanism for a different form of repetition. We might, for example, add up all the numbers in a list.