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: http://bit.ly/151-2014F-w42
• Reading for Tuesday:
  • Analyzing Procedures
• 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