Class 45: List ADTs

Held: Monday, April 25, 2005

Summary: Today we consider the design of various list ADTs.

Related Pages:

• EBoard.
• Sample Code.

Overview:

• What else is a list?
• Two ways to iterate lists: Cursors and Positions
• Three kinds of lists: Simple, Ordered, and Sorted

Types of Lists

• Scheme lists are more data structures than ADTs, since the focus is on the implementation.
• What can we say abstractly about lists?
• One solution: A list is, in essence, a collection of elements that you can iterate.
  • By iterate, I mean that you can visit the elements of the list one by one.
• We tend to think of three related kinds of non-Scheme lists:
  • Simple Lists are the simplest (as their name suggests). They are collections. They are iterable. That's about it. (In particular, the client does not get to control the order in which the elements are iterated.)
  • Sequenced Lists give the client control over the order in which the elements are iterated. You can talk about adding something before or after an element of an ordered lists.
  • Sorted Lists are iterated in sorted order (typically from smallest to largest).
• As the article you may have read long ago suggests, it helps to associate Cursors or Positions with lists.
  • Both provide ways of referring to places in the list.
  • Cursors do move. You can advance them to the next element or retreat them to the previous element.
  • Positions don't move: You ask for their successors or predecessors.
• As I've suggested before, one key way to think about abstract data types is to think about their key operations. Let's visit these.

A Cursor ADT

Left for class discussion.

A Position ADT

Left for class discussion.

A SimpleList ADT

Left for class discussion.

A SequencedList ADT

Left for class discussion.

A SortedList ADT

Left for class discussion.