--- title: Eboard 32 Analyzing procedures number: 32 section: eboards held: 2017-11-13 --- CSC 151.01, Class 32: Analyzing procedures =========================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Lab * Debrief ### News / Etc. * We finally get to analyzing procedures today. Sorry for the delay. * Please try to keep the room straight. * Exam 2 returned last night. If you didn't get it, let me know. * Quiz 11 returned. Some issues on `l-s` vs. `r-s` ### Upcoming Work * Reading for Wednesday: [Association lists](../readings/association-lists) * Since it was ready for today, it's still ready for Wednesday. * No writeup for class 31. * [Writeup for class 32](../writeups/writeup32) due Wednesday at 10:30 p.m. * Exercise 6 * To: * Subject: CSC 151.01 Writeup 32 (YOUR NAMES) * [Exam 3](../exams/exam03) * Exam due TOMORROW * Cover pages due Wednesday the 15th. * Epilogues due Wednesday the 15th. ### Extra credit (Academic/Artistic) * Convocation Thursday at 11 a.m. in JRC 101. "Work's Provocative Future: Which Graduates Will Thrive?" ### Extra credit (Peer) * "The First Time I Walked on the Moon". Five, count 'em, five performances. Th7:30 F7:30 S2, S7:30 Sun2:00 Flanagan Theatres * Orchestra, Satruday at 2pm ### Extra credit (Misc) ### Other good things * Fresh Flutes Thursday * Voice recitals Friday at 4:15 (Henderson) and 7:00 (Manuel) * Women's Basketball vs. Emmaus Wed at 5:00 p.m. * Men's Basketball vs. Emmaus Wed at 7:00 p.m. * Swimming and Diving Saturday at 1:00 p.m. ### Questions Could you help me understand the difference between left-section and right-section? : Sure. : Left section and right section both fill in one parameter to a two parameter procedure, leaving you with a one-parameter procedure. : Left section fills in the left parameter. : Right section fills in the right parameter. ; `(l-s fun x)` == `(section fun x <>)` ; `(r-s fun x)` == `(section fun <> x)` : If I want a procedure that divides by 2, the 2 should be on the right, and I want `(r-s / 2)`. : If I want a procedure that divides by n, the n should be on the right, and I want `(r-s / n)`. I'm having trouble with problem 4. Is there a pattern that will help? And can you help me understand that pattern? : Sure. ``` ;;; Procedure: ;;; number-vector-increment! ;;; Parameters: ;;; vec, a vector ;;; Purpose: ;;; Increment the value at all vector positions ;;; Produces: ;;; [Nothing; called for side effect.] ;;; Preconditions: ;;; (vector-ref vec index) for 0 <= index < (vector-length vec) is a number. ;;; number-vect-increment-at! is defined ;;; Postconditions: ;;; Let val be (vector-ref vec index) before the procedure call. After the ;; call (vector-ref vec index) produces val+1. (define number-vector-increment! (lambda (vec) (let ([len (vector-length vec)]) ; unchanging value, tells recursion to stop (let kernel! ([pos 0]) ; Start the recursion at the first position (when (< pos len) ; When the position is valid, (number-vector-increment-at! vec pos) ; increment the number at pos (kernel! (+ 1 pos))))))) ; and process the rest of the vector ``` Note that `number-vector-increment-at!` does a `vector-ref` and a `vector-set!`. I expect you'll want to do something similar. Do we have to return the vector for problem 4? : I would prefer that you *not* return the vector. : But if you choose to return the vector, you will not lose points for doing so. Lab --- What do you mean by "total calls"? : Include the counts for `car`, `cdr`, `cons`, `null?` and such. Why is `list-reverse-1` so much worse? : That's one of those things the lab is intended to get you to think about. : But it's because we're calling `list-append` repeatedly, and `list-append` needs to recurse through the first list. What is the writeup? : Exercise 6 Debrief ------- I know it's not part of this lab, but can we go over the tree recursion problem from the quiz? : Sure, if there's time.