Held: Wednesday, 26 February 2014

Back to Outline 22 - Images as Functions from Position to Colors. On to Outline 24 - Recursion Basics.

Summary

We explore further details of Scheme's lists. Lists are an important mechanism for structuring data. We also consider how lists can be used to represent drawings.

Related Pages

• Reading: Building Data Structures with Heterogenous Lists
• Lab: Building Data Structures with Heterogeneous Lists
• EBoard 23 (Source 23) (HTML 23) (PDF 23)

Overview

• Lists, revisited.
• New list operations.
• Drawings as values.

Administrivia

• Reading for Friday: Recursion Basics
• Writeup: Exercise 4
  • Subject: CSC 151.02 Writeup 15: Iterating Positions (OPTIONAL NAMES)
• Yay! We have a new homework assignment
• I have appointments across campus this afternoon starting at 2:15, so I'll be leaving immediately after class.
• Kim will be teaching class this Friday and next Tuesday.
• Would you prefer to have our awesome team of mentors or a guest lecturer on Wednesday and Friday?
• I'm giving up on the Thursday daytime review sessions. Sign up for individual appointments instead. (I've done my best to expand available times.)
• Extra credit:
  • Thursday CS Extras at 4:30 p.m. in 3821: New CS Curriculum.
  • Convo next Wednesday.

Lists

• Our first encounters with lists.
  • Collection of values
  • Homogeneous: All the values in a list are the same type
  • Used primarily with map and for-each
• Extending that notion
  • Can also be heterogeneous: Values in the list may have multiple types.
  • Can examine individual elements with car, cdr, and list-ref.
  • Can be extended (creating new lists) with cons.
  • There's an empty list: null.
• Why is the new view important?
  • It will soon give us the opportunity to manipulate lists in new and interesting ways.

Implementing Drawings

• We can (and do) use lists to implement drawings.
• The reading considers a simplified representation, in which the width and height of a drawing are the same.
• But the general process is the same
  • Group the values in a list
  • When we need to render or manipulate a drawing, use the list operations to extract parts.

Lab