Compound Data, Part 1: Structures

The input of a function is seldom a single measurement (number), a single switch position (boolean), or a single name (symbol). Instead, it is almost always a piece of data that represents an object with many properties. Each property is a piece of information. For example, a function may consume a record about a CD; the relevant information might include the artist's name, the CD title, and the price. Similarly, if we are to model the movement of an object across a plane with a function, we must represent the position of the object in the plane, its speed in each direction, and possibly its color. In both cases, we refer to several pieces of information as if they were one: one record and one point. In short, we COMPOUND several pieces of data into a single piece of data.

Scheme provides many different methods for compounding data. In this section, we deal with structures. A structure combines a fixed number of values into a single piece of data. In section , we will encounter a method for combining an arbitrarily large number of values into a single piece of data.

• Structures
• Extended Exercise: Drawing Simple Pictures
• Structure Definitions
• Data Definitions
• Designing Functions for Compound Data
• Extended Exercise: Moving Circles and Rectangles
• Extended Exercise: Hangman