--- title: Eboard 11 Boolean values, predicate procedures, and list filters number: 11 section: eboards held: 2017-09-18 --- CSC 151.03, Class 11: Boolean values, predicate procedures, and list filters ============================================================================= _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Notes from quiz 3 * Lab * Debrief ### News / Etc. * New partners. * Please rotate driver and navigator after each problem. * Please make sure to return your computer cards to the jar. * Thank you for all of the excellent exam questions. You will find many Q&A in the exam. * I did not have time to finish grading your quizzes this weekend. We will still go over them to help you understand what I expect for documentation and tests. ### Upcoming Work * [Writeup for class 10](../writeups/writeup10) due TONIGHT at 10:30 p.m. * Exercise 6 * To: * Subject: CSC 151.03 Writeup 10 (YOUR NAMES) * [Writeup for class 11](../writeups/writeup11) due Wednesday at 10:30 p.m. * Exercise 4c. No documentation is necessary. * To: * Subject: CSC 151.03 Writeup 11 (YOUR NAMES) * Read: [Local bindings](../readings/local-bindings) for Wednesday's class. * Read: [A computer scientist's perspective of data science](../readings/data-science) for Wednesday's class [Should be ready late tonight]. * Exam 1 * Exam due TOMORROW night * Cover sheet due Wednesday in class * Epilogue due Wednesday night ### Extra credit (Academic/Artistic) * CS Table, Tuesday, noon, PDR A: Activism * CS Extras, Thursday, 4:15 p.m., 3821, Study Abroad in CS * One of the Happy Kareoke Fun Time activities * Musical, Friday 9pm, Gardner. * Workshop: Burn your fear. Saturday, 2pm. The Wall. Email [improv] to sign up. * Workshop: Creating through improv. Sunday, 2pm. The Wall. Email [improv] to sign up. * Musical, Sunday, 7pm, Gardner ### Extra credit (Peer) * Women's soccer Saturday. * Women's soccer Sunday. ### Extra Credit (Misc) _None right now._ ### Other Good Things _None right now._ ### Questions Can I use `filter` to solve problem 5? : Not if you want credit for the problem. Can I still gain extra credit for all my peers by identifying errors in the exam? : Yes, until 10:30 p.m. Tuesday, when it is due. Can they get extra credit for errors in the Q&A section? : No. Then folks would be getting more than 100 points of extra credit. Notes from quiz 3 ----------------- ### Part a: Documenting nearest multiple ``` ;;; Procedure: ;;; nearest-multiple ;;; Parameters: ;;; val, a real number ;;; n, an integer ;;; Purpose: ;;; Finds the nearest multiple of n to val. ;;; Produces: ;;; result, a real number ;;; Preconditions: ;;; n > 0 ;;; Postconditions: ;;; * result is an integer multiple of n. There exists an integer k ;;; s.t. k*n = result. (Alternately: n evenly divides result, ;;; (remainder result n) = 0. ;;; * result is the nearest multiple. That is, for all other multiples ;;; of n (say, m), we know that |val - result| <= |val - m| ``` * Don't rename parameters unless it makes them clearer. E.g., `val1` and `val2`. * Don't forget to give a name to the product * Don't forget to give a type * Your reader may not understand "multiple". For example, 7 is a multiple of 2. Becuase when I multiply 2 by 3.5 I get 7. * Parameters vs. Preconditions: Limitations on the input. Parameters the "easy" limitations (types). Preconditions are whatever is left (e.g., "not zero"; a > b, ...) * Purpose vs. Postconditions: Both describe what the procedure does. Purpose informally; most people will understand. Postconditions: More formal, try to avoid terms that people may not share a definition of. * It would be fine to say `n` is an integer or real. However, you probably need a precondition that it's not zero. * What should `(nearest-multiple 10 4)` return? (We are vague on this; that's okay. It can return either 8 or 12.) ### Part b: Testing * Particularly if you only have four tests, test different things. * Write tests that have a clear answer. * *not* `(nearest-multiple 0 0)`. * *not* `(nearest-multiple 10 4)`. Lab and Debrief --------------- How should I compare two strings for equality? : `string=?` and `string-ci=?` tend to be the two best options. : **Do not use `eq?` or `eqv?`!** Do you care whether or not I use lambda when I can use compositions/section? : Nope. Some people prefer lambda. Some prefer section/compose. You'll generally find that the latter are shorter, but perhaps not much. ``` (define in-iowa? (lambda (row) (string-ci=? "IA" (list-ref row 4)))) (define in-iowa? (o (section string-ci=? <> "IA") (section list-ref <> 4))) ``` What is the difference between `not` and `negate`? : `not` takes a Boolean value as an input and returns the "opposite" Boolean value. : `negate` takes a predicate as an input and returns a new predicate that returns the opposite result : For example, ``` > (not #t) #f > (not #f) #t > (not 2) #f > (not real?) #f > (negate real?) # > (define something? (negate real?)) > (something? 1) #f > (something? "") #t > (something? (list 1 2 3)) #t > (something? something?) #t ``` Anything else? : Remember the mantra: "Write something that works on individual elements or pairs of elements. Then apply it to the list with `map` (unary), `reduce` (binary), `sort` (binary comparator), or `filter` (unary predicate)."