CSC151.01 2014F, Class 17: Boolean Values and Predicate Procedures ================================================================== _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * Questions on today's topics. * Quiz. * Lab. Preliminaries ------------- ### Admin * New lab partners! * Welcome parents! (when I checked at 9am, none had signed up, but I'd rather be optimistic) * Fruit (snacks) * Office hours: Today, 1:45-3:15; Also walking hours 1:15-1:45. Monday's hours are distorted by prospective student events. I'll try to stay around later in the day than normal. * The prologues suggest that you are anticipating about 3-4 hours on the HW. That's my goal, too. Let me know where you are after 2 or so hours. * Let me know by Monday if you want to work alone on HW 5. * A few of you have said that you cannot sign the second academic honesty statement. I am currently debating what to do next. If you have suggestions, send them anonymously on the questions page. * It's Friday. I hope you have a chance to restore this weekend. Please be thoughtful about your choices this weekend (and not just because there are lots of families on campus). ### Upcoming Work * No lab writeup today (no matter what it says online). * Reading for Monday: * [The GNU Image Manipulation Program](../readings/gimp-reading.html) * [Programming the GIMP Tools](../readings/gimp-tools-reading.html) ### Extra Credit Opportunities #### Academic * CS Table today: Privacy and Big Data in the Social Sciences * Campus Town Hall September 30 t 7:30 p.m. * CS extras next Thursday: Alumni * CS table next Friday: Serendipity and Computing (with Grinnell's Artist in Residence) * Grinnell Prize events the following week (particularly events related to the prize winners whose project involves Web tools) #### Peer Support * Science poster session, Sat., Sept. 27, morningish, science elbow * Football Games (Saturday, Sept. 27, at 1pm) * Noteworthy, Sat., Sept. 27, 3:30 p.m. Herrick * Men's Tennis (???) * Women's Tennis (???) * Swimming (???) * Anna Christie, Oct. 9-12 (SB plays Marthy) * Evan's radio show 5pm Friday nights on KDIC * Donna's radio show Sunday midnight on KDIC #### Miscellaneous * Participate in #GrinWell. * Friends of Drake Library needs help setting up for their annual booksale on Thursday, October 2 (conveniently, the same night as Grinnell High School's homecoming parade). You can help a good cause and probably get a few free books, too. * Update: They can also use help on Wednesday, October 1. ### Questions Boolean values -------------- _What's the difference between a "keyword" and a "procedure"?_ > Procedures are parameterized collections of instructions. Call with `(PROCEDURE inputs)` > There are a number of things in Scheme that look like procedures, in that we write `(THING values)`. Scheme interprets these slightly differently. > For a procedure: `(* (+ 1 2) (* 3 4))` we always evaluate the parameters before we apply the operation. `(* alpha 4)` It depends on what we know about alpha. If we know nothing, we get an error. If it's not a number, we get an error. > (define alpha (+ 2 3)). Something that looks like a procedure, but acts diffently. Also not (define (max ...) 5) > We need a way to name things that are like procedures, but which have a different semantics of evaluation. We call them "keywords". > Keywords that you have encountered: `define`, `lambda` > New keywords introduced in this reading: `and`, `or`, `not` > `and` has a different order of evaluation. We look at each parameter one at a time, rather than evaluating them first. (Similar for `or`.) _Can you explain the "beyond the truth binary" section?_ > yadda yadda yadda _Why would we do `and` with non-truth values?_ > Most frequent reason. I want to do THIS then THIS then THIS, but stop if any of them fail. _Can you be more detailed?_ > Not right now.