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
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)) (let-syntax ((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)))