Top Level or Not Dependent Scheme Macro Expansion

Question

Is it possible to write a macro in Scheme that expands differently depending upon whether the macro was used at the top level or internally? I'm primarily interested in a solution that works in Guile Scheme.

Answer 1

If you mean "internal" in the sense of internal definitions, then it might work to have the macro redefine itself in the nested scope.

(define inner-transformer
  (syntax-rules ()
    [(_ (id a ...) e1 e2 ...)
     (define (id a ...)
       (format #t "inner func ~a\n" 'id)
       (let () e1 e2 ...))]))

(define-syntax func
  (lambda (x)
    (syntax-case x ()
      [(k (id a ...) e1 e2 ...)
       #'(define (id a ...)
           (let-syntax ([k inner-transformer])
             (format #t "top func ~a\n" 'id)
             (let () e1 e2 ...)))])))

(func (foo x)
  (func (bar y)
    (func (baz z)
      (+ x y z))
    (baz y))
  (bar x))

(foo 1)

Guile result:

top func foo
inner func bar
inner func baz
$1 = 3