1.3.3 Entry format

Chapters 4 and 6 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

[[category]] template

for required, primitive features, or

[[qualifier category]] template

where qualifier is either "library" or "optional" as defined in section 1.3.1.

If category is "syntax", the entry describes an expression type, and the template 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

    <thing1> ...

indicates zero or more occurrences of a <thing>, and

    <thing1> <thing2> ...

indicates one or more occurrences of a <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

Procedure:  (vector-ref vector k)

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

Procedure:  (make-vector k)
Procedure:  (make-vector k fill)

indicate that the make-vector procedure must be defined to take either one or 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 3.2, 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:

obj

any object

list

list (see section 6.3.2)

z

complex number

x

real number

y

real number

q

rational number

n

integer

k

exact non-negative integer