4.2.1 Variables definitions

The define form described in this section is a ?definition used to create variable bindings and may appear anywhere other definitions may appear.

Syntax: define ?variable ?expression

Syntax: define ?variable

Syntax: define (?variable ?formals) ?body

Syntax: define (?variable . ?formal) ?body

The first from of define binds ?variable to a new location before assigning the value of ?expression to it.

(define add3
  (lambda (x) (+ x 3)))
(add3 3)                            ⇒  6
(define first car)
(first '(1 2))                      ⇒  1

The continuation of ?expression should not be invoked more than once.

Implementation responsibilities: Implementations should detect that the continuation of ?expression is invoked more than once. If the implementation detects this, it must raise an exception with condition type &assertion.

The second form of define is equivalent to:

(define ?variable ?unspecified)

where ?unspecified is a side–effect–free expression returning an unspecified value.

In the third form of define, ?formals must be either a sequence of zero or more variables, or a sequence of one or more variables followed by a dot . and another variable (as in a lambda expression). This form is equivalent to:

(define ?variable
  (lambda (?formals) ?body))

In the fourth form of define, ?formal must be a single variable. This form is equivalent to:

(define ?variable
  (lambda ?formal ?body))