Overview

• Preliminaries.
  • Admin.
  • Updates on due dates.
  • Questions on the project.
• Big Picture Issues.
  • Some program design principles.
  • Thinking about repetition.
• Procedures as first-class values.
• What's the difference between apply, map, and for-each?
• Lab.

Preliminaries

Admin

• Pictures!
• Today's lab writeup (#26): Turn in 3, 4.
• I hope to get your project proposals reviewed by Thursday night.
• Upcoming extra credit opportunities:
  • Basketball tonight at 5:30 pm.
  • Seth performs at Relish tonight at 10pm.
  • CS Table, Friday, The New Curriculum.
  • Hamlet, Friday (7:30pm), Saturday (7:30pm), Sunday (2pm).
  • Swimming, Saturday, 10 am
  • Chamber Ensemble, Saturday, 7:30 pm.
  • Typhoon Halyan Relief benefit show, Sunday, November 24th from 7-9pm in Harris. (If the entry fee is a burden, let me know and I'll give you the money.)
  • "Data Sovreignty: The Challenge of Geolocating Data in the Cloud", November 25, 4:15 JRC 101
  • Showing of "Gold Fever" by Andrew Shurburne '01 or so, 7:00 p.m. Monday, November 25, ARH 302
  • Tuesday, November 26, 4:15 p.m., JRC 209 a gaming event with the game [d0x3d!] Popcorn will be served.

Watch Sam Screw Up Due Dates

Planned (but not quite what was on the Web site)

• Project due Tuesday, November 25th
• Exam due Monday, December 9th

Revised

• Project due Tuesday, December 3rd
• Exam due Tuesday, December 10th
• 2 point bonus for turning in the exam on Monday, December 9th

Questions

Are subtle progressions ok?

Yes

Can it be representational?

Yes

Can it be representational and good?

Past evidence suggests no.

Some program design principles

• More efficient code is better.
  • Don't do a computation twice if you can do it once.
  • let is your friend
• Don't program by copy-paste-change
  • Mistake-prone
  • Hard to update!
  • Solution: Factor out the common parts
  • More efficient use of programmer time

Thinking about repetition

• See outline
• Once you understand a control structure, encapsulate it into something general, and use the general thing
• Example map

Procedures as first-class values

• We can write procedures that take other procedures as parameters (e.g. map - apply a procedure to each value in a list)
• We can write procedures that create new procedures (e.g. l-s)
• Procedures are just another kind of value
• A new type!
  • How do we write them? (lambda (params) body)
  • How do we create values? compose, section, ...
  • What kinds of functions can we apply to the values we create? map, compose, section, apply

Some related proedures - apply vs. map

• apply: Given a procedure and a list, "applies the procedure to the list"
  • For map, we mean "apply the procedure to each element of the list separately"
  • For apply, we mean "take the elements of the list, and make them parameters for ONE procedure call."
• (apply + (list 1 2 3)) => (+ 1 2 3)
• (map + (list 1 2 3)) => (list (+ 1) (+ 2) (+ 3))

Lab