Syntax Expansion and Internal Definitions

All binding forms are macro expanded into define-values, let-values, and letrec-values expressions. The set!-values form is expanded to let-values with set!. See section 13.4 for more information.

All define-values expressions that are inside only begin expressions are treated as top-level definitions. Immediate body define-value expressions in a unit expression are handled specially as described in section 7.1.1. Any other define-values expression is either an internal definition or syntactically illegal.

Internal definitions can appear at the beginning of the body in a lambda, case-lambda, let, let-values, let*, let*-values, letrec, letrec-values, fluid-let, let-macro, let-id-macro, let-expansion-time, parameterize, or with-handlers expression. At least one non-definition expression must follow a sequence of internal definitions.

When a begin expression appears within an implicit sequence, its content is inlined into the sequence (recursively, if the begin expression contains other begin expressions). Like top-level begin expressions (and unlike other begin expressions), a begin expression in an internal definition context can be empty.

An internal define-values expression is transformed along with the rest of the expressions following it into a letrec-values expression: the variables originally bound by the define-values expressions become the binding variables of the new letrec-values expression, and the expressions that followed the define-values expressions become the body of the new letrec-values expression.

Multiple adjacent define-values statements are collected into a single letrec-values transformation so that the definitions can be mutually-recursive, but the define-values expressions really must be adjacent: a define-values expressions following a non-define-values expression is not an internal definition.

An internal definition cannot shadow a syntax form or macro name. Thus, an internal definition cannot alter the decision of whether another expression is also an internal definition in the same letrec-values transformation.

Internal macro definitions (using define-macro) are described in section 13.1.