CSC151.01 2014F, Class 42: Higher-Order Procedures, Revisited ============================================================= *New partners!* _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Notes on the project. * Questions. * Introductory comments. * Some program design principles. * Thinking about repeated work. * Procedures as first-class values. * Reflection. * Lab. Preliminaries ------------- ### Admin * Exam 3 returned at the end of class. * Notes to be distributed this evening. * Quizzes to be returned tomorrow. * Office hours recomplicated by interviews and administrative junk. Sorry. * Right now, I don't even know what they are or will be. * Today's topic is complex; I assume we'll have more questions than normal. ### Upcoming Work * Lab writeup: Exercises 3 & 4: * Reading for Tuesday: * [Analyzing Procedures](../readings/analysis-reading.html) * Part one of the project due tonight! * Sketches due in class on Tuesday. * Part two of the project due next Tuesday. ### Extra Credit Opportunities #### Academic * CS Extras Thursday: Weinmaniacs on Text Recognition in Maps * CS Table Friday: One Year After Healthcare.gov * CS Extras Tuesday the 25th: Summer Opportunities in CS #### Peer Support * Why didn't anyone mention the ISO dinner? * Karan's radio show 11pm Thursday nights on KDIC * Evan's radio show 5pm Friday nights on KDIC * Donna's radio show Sunday midnight on KDIC * One acts, coming soon #### Miscellaneous * VP Student Affairs Candidate Open Sessions * Wednesday, 4:15, JRC 209 * Friday, 4:15, JRC 209 ### Project Notes * Remember that you need at least three different approaches from the menu of Gimp tools, Turtles, image-compute, image-variant, drawings as values, and color trees. (If you want to suggest another, ....) * `(image-redo! image (lambda (x y color) newcolor))` is the generalization of `image-transform!` and `image-compute`. * Can we use `turtle-teleport!` and `turtle-face!`? Yes. ### Questions Some program design principles ------------------------------ * Hope: How to write "elegant" algorithm * Keep it small, if possible * Potentially more efficient * Faster to write (for the programmer) (map (l-s + 4) (iota 10)) vs. recursive * Potentially more readable * Don't rewrite nearly-identical code * let helps us handle this issue * Helper functions that encapsulate the similarity * Only name the things that have to be named Thinking about repeating work ----------------------------- * Reading three variants of the same approach teaches you something; after that, more reading doesn't help * Writing three variants of the same approach teaches you something; after that, more writing doesn't help * Ideally, we should be able to generalize any approach we use (and turn it into a function) Procedures as first-class values -------------------------------- * When you generalize, you might want to have procedures as parameters (as in `map`) or return procedures as values (as in `l-s`). * Scheme lets you do this. Not all languages do. Reflection ---------- What did you learn from the reading? What do you still find puzzling or murky? * What's the diff between apply and map? Lab ---