CSC151.01 2014F, Class 20: Anonymous Procedures =============================================== * Keep your partners from yesterday.* _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * A quick note on HW 4 * A few notes on yesterday's lab * Questions on the reading * From you * From me * Lab Preliminaries ------------- ### Admin * Office hours (modified due to way too many meetings): * Thursday 8:00-9:45, 2:30-3:15 * Friday 2:15-3:15 * Review session Thursday at 10:00 a.m. * Review sessions Wednesday and Thursday night at 8 p.m. ### Upcoming Work * [HW 5](../assignments/assignment.05.html) assigned. * No lab writeup from today. * Reading for Friday: * [Local Bindings](../readings/let-reading.html) ### Quiz Topics *Reminder: You may bring a sheet of notes to Friday's quiz.* * Lists (using `list`, `make-list`, and `iota`) * `map` * More simple lambda expressions * Conditionals * GIMP procedures (e.g., `image-select-rectangle!`) * `compose`, `o`, `l-s`, `r-s` (the latter two from today's class) ### Extra Credit Opportunities #### Academic * CS extras Thursday at 4:30: Alumni * CS table 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 * Concert tonight. * Football (???) * Men's Tennis (???) * Women's Tennis (???) * Swimming (???) * Evan's radio show 5pm Friday nights on KDIC * Donna's radio show Sunday midnight on KDIC * Anna Christie, Oct. 9-12 (SB plays Marthy) ### Questions (Administrative, Recent Topics, Etc.) Followup Notes from Tuesday --------------------------- Two ways to write `irgb-brighter?` (define irgb-brighter? (lambda (color1 color2) (if (> (rgb-brightness color1) (rgb-brightness color2)) #t #f))) vs. (define irgb-brighter? (lambda (color1 color2) (> (rgb-brightness color1) (rgb-brightness color2)))) Multiple ways to write `irgb-4grey` with `if`? (define irgb-4grey (lambda (color) (if (< (irgb-brightness color) 0.25) grey1 (if (and (< (irgb-brightness color) 0.5) (>= (irgb-brightness color) 0.25)) grey2 (if (and (< (irgb-brightness color) 0.75) (>= (irgb-brightness color) 0.5)) grey3 (if (and (<= (irb-brightness color 1.0)) (>= (irg-brigthness color 0.75))) grey4 0)))))) vs. (define irgb-4grey (lambda (color) (if (< (irgb-brightness color) 0.25) grey1 (if (and (< (irgb-brightness color) 0.5) (>= (irgb-brightness color) 0.25)) grey2 (if (and (< (irgb-brightness color) 0.75) (>= (irgb-brightness color) 0.5)) grey3 grey4))))) vs. (define irgb-4grey (lambda (color) (if (<= (irgb-brightness color) 0.25) grey1 (if (<= (irgb-brightness color) 0.5) grey2 (if (<= (irgb-brightness color) 0.75) grey3 grey4))))) vs. (define brightness-4grey (lambda (brightness) (if (<= brightness 0.25) grey1 (if (<= brightness 0.5) grey2 (if (<= brightness 0.75) grey3 grey4))))) (define color-4grey (lambda (color) (brightness-4grey (irgb-brightness (color->irgb color))))) vs. (define irgb-4grey (lambda (color) (if (<= 0 (irgb->brightness color) 0.25) grey1 (if (<= 0.25 (irgb-brightness color) 0.5) grey2 (if (<= 0.5 (irgb-brightness color) 0.75) grey3 grey4))))) Followup to HW 4 ---------------- (define apply-transform (lambda (transform irgb-color) (transform irgb-color))) (define visualize-transforms (lambda (irgb-color list-of-transforms number-of-transforms) (visualize-colors (map apply-transform list-of-transforms (make-list number-of-transforms irgb-color)) number-of-transforms))) vs. (define visualize-transforms (lambda (irgb-color list-of-transforms number-of-transforms) (visualize-colors (map (lambda (trans) (trans irgb-color)) list-of-transforms) number-of-transforms))) Your Questions on the Reading ----------------------------- _What's the point of `l-s` and `r-s`?_ > Lets you write shorter (and more readable?) code (map (l-s * 2) (iota 5)) (map (lambda (x) (* 2 x)) (iota 5)) _What do left section and right section do?_ > Fill in one of the parameters for a two-parameter procedure. > left-section fills in the first parameter. right-section fills in the second > (map (l-s / 2) (iota 5)) ; (map (lambda (val) (/ 2 val)) (iota 5)) ; (list (/ 2 0) (/ 2 1) (/ 2 2) (/ 2 3) (/ 2 4)) > (map (r-s / 2) (iota 5)) ; (map (lambda (val) (/ val 2)) (iota 5)) (list (/ 0 2) (/ 1 2) (/ 2 2) (/ 3 2) (/ 4 2)) _Can you explain this weird code? `(map (o increment (l-s * 2) (r-s mod 7)) (iota 50))` > Start with > (map (o (r-s mod 7)) (iota 20)) ; (map (lambda (x) (mod x 7)) '(0 ... 19)) > (map (o (l-s * 2) (r-s mod 7)) (iota 20)) ; (map (l-s * 2) '(0 1 2 3 4 5 6 0 1 2 3 4 5 6 ...)) 0 2 4 8 10 12 0 2 4 8 10 > (map (o (r-s mod 7)) (iota 20)) '(0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5) > (map (o (l-s * 2) (r-s mod 7)) (iota 20)) '(0 2 4 6 8 10 12 0 2 4 6 8 10 12 0 2 4 6 8 10) > (map (o (l-s mod 7)) (iota 20)) . . share/lib/gigls/higher.rkt:256:20: modulo: undefined for 0 > (map (o (l-s mod 7)) (drop (iota 20) 1)) '(0 1 1 3 2 1 0 7 7 7 7 7 7 7 7 7 7 7 7) > (map (o increment (l-s * 2) (r-s mod 7)) (iota 20)) '(1 3 5 7 9 11 13 1 3 5 7 9 11 13 1 3 5 7 9 11) My Questions on the Reading --------------------------- *Discuss each of these with your partner and be prepared to answer.* a. What is the difference between `(l-s + 2)` and `(r-s + 2)`? b. What is the difference between `(l-s - 2)` and `(r-s - 2)`? c. What is the difference between `(o increment sqrt)` and `(o sqrt increment)`? Lab --- For the extras, we want things like ; Compose f and g. Return the function that, given an input ; x, applies g to x and then f to x. ; In math notation, (fog)(x) = f(g(x)) (define my-compose (lambda (f g) (...)))