The Scheme Vocabulary

Scheme's basic vocabulary consists of five categories of words. The five lines in figure  show how computer scientists discuss the vocabulary of a language. All lines employ the same notation. They enumerate some simple examples separated by a bar (`` ''). Dots indicate that there are more things of the same kind in some category.

Figure: Beginning Student Scheme: The core vocabulary

The first category is that of variables, which are the names of functions and values. The second introduces constants: boolean, symbolic, and numeric constants. As indicated before, Scheme has a powerful number system, which is best introduced gradually by examples. The final category is that of primitive operations, which are those basic functions that Scheme provides from the very beginning. While it is possible to specify this collection in its entirety, it is best introduced in pieces, as the need arises.

For the classification of Scheme sentences, we also need three keywords: define, cond, and else. These keywords have no meaning. Their role resembles that of punctuation marks, especially that of commas and semicolons, in English writing; they help programmers distinguish one sentence from another. No keyword may be used as a variable.