Held: Tuesday, 6 October 2015

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
• Reference: Important List Procedures
• EBoard 23 (Source 23)

Overview

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

Administrivia

• Continue partners!

Upcoming Work

• Reading for Wednesday: Recursion Basics
  • Warning! For some, this will be even more confusing than section. For others, it will be intuitive. We will spend a few weeks trying to make it intuitive for everyone.
• HW 5 due tonight.
• Today's Lab writeup (due before class Friday)
  • Email to grader-151-01@cs.grinnell.edu
  • Subject: CSC 151 Lab Writeup Class 23 (Your Names)
  • Exercise:
• Exam 2 distributed.
  • We'll go through it quickly.
  • Probably lots of opportunities for corrections :-)

Extra Credit Opportunities

• If possible, send me these in advance.

Academic

• Any visit to the current show in the Faulconer gallery
• CS Table today: Barbie and the "Internet of Things"
• CS Extras Thursday: Blake Creasey on Watson

Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included), Sunday at 4:45, and Mondays at 4:45. Requires sign up in advance.
• Pun Club, Saturdays, 4pm, Way over Younker.

Other Good Things

• Friends of Drake Library book sale this weekend. Friday 5-8 pm. Saturday 8am-2pm. Admission $3 on Friday and $0 on Saturday.

Lists

• Our first encounters with lists.
  • Collection of values
  • Homogeneous: All the values in a list are the same type
  • Used primarily with map
• 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