(require (for-syntax racket/base racket/list))

(define-syntax (queens stx)
  (syntax-case stx ()
    [(_ n)
     (with-syntax ([board (datum->syntax
                           stx
                           (cons 'list
                                 (for/list ([_ (syntax->datum #'n)])
                                   `(amb ,@(range 1 (add1 (syntax->datum #'n)))))))])
       #`(amb-collect
          (let ([b board])
            (amb-assert (distinct? b))
            (amb-assert (safe? b))
            b)))]))

(queens 1)
(queens 4)
(queens 6)