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5.3 Syntax definitions

Syntax definitions are valid only at the top level of a <program>.

They have the following form: (define-syntax <keyword> <transformer spec>)

<Keyword> is an identifier, and the <transformer spec> should be an instance of syntax-rules. The top-level syntactic environment is extended by binding the <keyword> to the specified transformer.

There is no define-syntax analogue of internal definitions.

Although macros may expand into definitions and syntax definitions in any context that permits them, it is an error for a definition or syntax definition to shadow a syntactic keyword whose meaning is needed to determine whether some form in the group of forms that contains the shadowing definition is in fact a definition, or, for internal definitions, is needed to determine the boundary between the group and the expressions that follow the group. For example, the following are errors:

     (define define 3)
     (begin (define begin list))
       ((foo (syntax-rules ()
               ((foo (proc args ...) body ...)
                (define proc
                  (lambda (args ...)
                    body ...))))))
       (let ((x 3))
         (foo (plus x y) (+ x y))
         (define foo x)
         (plus foo x)))