CSC151.01 2015S, Class 20: Anonymous Procedures, Revisited ========================================================== * New partners! _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * Conditionals, Revisited. * Anonymous Procedures, Revisited. * Lab. * Reflection. Preliminaries ------------- ### Admin * Review session tonight at 7pm. * I hope you had a great weekend and a great two days without me. I think I've caught up on all of the email questions I've received. If not, let me know. * Office hours today at 11:00 a.m. and 3:15 p.m. Office hours Tuesday at 10:00 a.m. * * Remember that if you invoked "There's More To Life" on the exam, you need to meet with me. ### Upcoming Work * [Homework 5](../assignments/assignment.05.html). * Due Tuesday at 10:30 p.m. * Note that 6P-style documentation is expected for every primary procedure you write. * Lab writeup for today: Exercise 5, parts b-f, * Reading for Tuesday * [Local Bindings](../readings/local-bindings-reading.html) ### Extra Credit Opportunities #### Academic * Pioneer Diversity Council Diversity Dialogue, 8:30 p.m. 26th, Main Quad "Academic Athletes and Academic Students". *Note new date!* #### Peer Support (Morning Section) * Julia's radio show, "The Hot Box". Wednesday night/Thursday morning 1:00-2:00 a.m. * Host a prospie. * Neverland Players Friday and Saturday at 7:30, Sunday at 1:30 and 7:30 * Nobody Gets Hurt, a show with an audience of one. Info on trying to get one of the tickets is on the posters. * Indoor Track and Field Championships this weekend. ### Other Good Things * ??? ### Questions _How do I copy and paste from images?_ ;;; Procedure: ;;; image-copy-paste-block! ;;; Parameters: ;;; source, an image id ;;; source-col, an integer ;;; source-row, an integer ;;; target, an image id ;;; target-col, an integer ;;; target-row, an integer ;;; width, an integer ;;; height, an integer ;;; Purpose: ;;; Copy a width-by-height block from source to target, with the ;;; top-left corner of each block as specified. ;;; Produces: ;;; [Nothing; called for the side effect.] ;;; Problems: ;;; Does not do well with improper column/row pairs (e.g., those ;;; outside the bounds of the image. _I'm having trouble with problem 2. Any hints?_ > Start by making sure you understand the problem, perhaps by working things through by hand. (visualize-transforms (color->irgb "pink") (list (lambda (irgb-color) irgb-color) irgb-darker (o irgb-darker irgb-darker) (o irgb-darker irgb-darker irgb-darker) (o irgb-darker irgb-darker irgb-darker irgb-darker)) 5) > There are three parameters. The first is a color. (Is it an integer-encoded RGB color, a color name, or a list of the red/green/blue components or ...?) Integer-encoded IRGB color. Second is a list of transformations. What's a "transformation"? It's a function from irgb values to irgb-values. The 5 is the number of transformations you have. (It's used as a parameter to visualize-colors, so we include it here for convenience. The `length` procedure would also allow us to compute it.) > Goal (for this call): Apply each of these five transformations to the pink color, make a shape in each color, and show the five shapes. > (define c (color->irgb "pink")) > c 16761035 > (define t1 (lambda (irgb-color) irgb-color)) > (t1 c) 16761035 > ((lambda (irgb-color) irgb-color) c) 16761035 > (define t2 irgb-darker) > (t2 c) 15708347 > Now we are ready to put them in a list and then show them > (visualize-colors (list 16761035 15708347 ...) 5) > Decompose problems. You want to make a list of colors, and then use `visualize-colors`. > How do you make the list of colors? Well, given a list of transformations of the form `'(t1 t2 t3 t4 t5)`, you want to make the list that contains the values `(t1 irgb-color)`, `(t2 irgb-color)`, `(t3 irgb-color)`, `(t4 irgb-color)`, and `(t5 irgb-color)`. > Given one list, you make another list with an appropriate call to `map`. Your challenge is to write that call. _How do you write post-conditions for a procedure that returns a procedure?_ > Option 1: ;;; Produces: ;;; proc, a procedure ;;; ... ;;; Postconditions: ;;; proc has the form (proc param1 param2) where param1 is a ;;; an integer and param2 is an image id. proc computes ... > Option 2: ;;; Produces: ;;; proc, a procedure from integers and image ids to image ids. ;;; ... ;;; Postconditions: ;;; (proc param1 param2) has the value ... > Option 3: ;;; Produces: ;;; proc, a procedure ;;; ... ;;; Postconditions: ;;; proc meets the following specifications ;;; Parameters: ;;; param1, an integer ;;; param2, an image id ;;; Purpose: ;;; ... ;;; Produces: ;;; image, an image id ;;; Preconditions: ;;; [No additional] ;;; Postconditions: ;;; ... _In Problem 4 on Assignment 5, does "a simple shape of your choice" mean that the user can customize a shape, or that the programmer decides what shape to use?_ > I was assuming that you, in implementing the procedure, would decide what the shape would be. Conditionals, Revisited ----------------------- You learned three new mechanisms for conditional evaluation: `if`, `when`, and `cond`. What are the similarities and differences between them? Why might you use one over another? * `if` is when you have one condition and you want to choose between two options. * `cond` is when you have multiple conditions * `when` is for when you have one condition and no alternative if the condition doesn't hold (that is, you don't want to do anything if the condition doesn't hold) * They have slightly different syntax/number of parameters * In `if`, the options can only be a single expression; in `when` and `cond`, the options can be multiple expressions, which are evaluated in turn. Many Scheme programmers consider `and` and `or` additional mechanisms for conditional evaluation. Why? Anonymous Procedures, Revisited ------------------------------- The reading was intended partially as review and partially to introduce new ideas. What new things did you learn about anonymous procedures?