[plt-scheme] syntax-case vs. #lang scheme/base

I'm probably being wayyyy stupid:

So I'm trying to write some code with #lang scheme/base and syntax-case,
following the guide, as far as I know:

#lang scheme/base

(define-syntax foo
  (lambda (stx)
    (syntax-case stx ()
      ((_ ?bar) ?bar))))

I get:

. compile: bad syntax; function application is not allowed, because no #%app syntax transformer is bound in: (lambda (stx) (syntax-case stx () ((_ ?bar) ?bar)))

Following suggestions from previous posts, I've tried various
incantations of `require-for-syntax' and `require-for-template', but to
no avail.

Help would be much appreciated!

-- 
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla