#lang scheme

(provide define-if-unbound)

;; Simpler than version-case
(define-syntax (define-if-unbound stx)
  (syntax-case stx ()
    [(form (header . rest) . body)
     (syntax/loc stx (form header (lambda rest . body)))]
    [(_ name expr)
     (if (identifier-binding #'name)
         (syntax/loc stx (begin))
         (syntax/loc stx (define name expr)))]))