Entry format

Chapters  and  are organized into entries. Each entry describes one language feature or a group of related features, where a feature is either a syntactic construct or a built-in procedure. An entry begins with one or more header lines of the form

templateessential category

if the feature is an essential feature, or simply

templatecategory

if the feature is not an essential feature.

If category is ``'', the entry describes an expression type, and the header line gives the syntax of the expression type. Components of expressions are designated by syntactic variables, which are written using angle brackets, for example, expression, variable. Syntactic variables should be understood to denote segments of program text; for example, expression stands for any string of characters which is a syntactically valid expression. The notation

        thing …

        thing thing …

If category is ``procedure'', then the entry describes a procedure, and the header line gives a template for a call to the procedure. Argument names in the template are italicized. Thus the header line

(vector-ref vector k)essential procedure

indicates that the essential built-in procedure vector-ref takes two arguments, a vector vector and an exact non-negative integer k (see below). The header lines

(make-vector k)essential procedure (make-vector k fill)procedure

indicate that in all implementations, the make-vector procedure must be defined to take one argument, and some implementations will extend it to take two arguments.

It is an error for an operation to be presented with an argument that it is not specified to handle. For succinctness, we follow the convention that if an argument name is also the name of a type listed in section , then that argument must be of the named type. For example, the header line for vector-ref given above dictates that the first argument to vector-ref must be a vector. The following naming conventions also imply type restrictions:

Provide an example entry??