Overview

• Preliminaries.
  • Admin.
  • Questions.
  • Quiz.
• Representing lists: Pairs and cons cells.
• Why care about the underlying representation?
• Lab!

Preliminaries

Upcoming Work

• Reading for Monday: Trees
• Homework for next Tuesday: HW 8: Producing Playful Polygons
• Today's lab writeup: Exercise 4

Admin

• When I send you criticisms on lab writeups, there is no need to redo the writeup.
• I've returned most HW 7's. Sorry for the difficult parts (which weren't intentionally difficult)
• Continue this week's partner assignments.
• Extra credit:
  • Math/Stats seminar monday: Cuong Nguyen '14, Noon, somewhere in Math/Stat

Questions

Can you talk about backslashes in strings and characters?

Characters. Problem: Distinguish the character a from the string a from the symbol a from the name a. Scheme decided: characters #\a, "a", 'a, a.

Strings. Sequences of characters surrounded by double-quotation marks. "KimS is so excited." If quotation marks appear within a string, preface them with a backslash. "Kim S says \"I'm so excited!\"" And when things are in quotation marks, you don't need the #.

Whoops. Backslash has a special meaning. So .... to represent backslash in a string, write \. This lets us distingish "\" "\""

What does (list-drop lst n) do?

Creates a new list by removing the first n elements of lst. You can also think of this as (cdr (cdr (cdr ... (cdr lst)))), with n calls to cdr.

Quiz

Wasn't that fun?

Representing lists: Pairs and cons cells

Why care about the underlying representation?

• Some people think better from pictures.
• Helps us understand why some things work the way they do.
• Reminds us about costs.

Lab

Correction: NO LAB WRITEUP!