Compound Data, Part 2: Lists

Structures are one way to represent compound information. They are useful when we know how many pieces of data we wish to compound into one piece. In many cases, however, we don't know how many things we wish to enumerate, and in that case we form a list. A list can be of arbitrary length, that is, it contains a finite, but undetermined pieces of data.

Forming lists is something that all of us do. Before we go grocery shopping, we often write down a list of items that we want to purchase. When we plan out a day in the morning, we write down a list of things to do. During December, many children prepare Christmas wish lists. To plan a party, we list the people we want to invite. In short, arranging information in the form of lists is a ubiquitous part of our life, and we should learn to represent lists as Scheme data. In this section, we first learn to create lists and then move on to developing functions that consume lists.

• Lists
• Data Definitions for Lists of Arbitrary Length
• Processing Lists of Arbitrary Length
• Designing Functions for Self-Referential Data Definitions
• More on Processing Simple Lists