; Just to show that it can be done: the following syntax transformer ; expands (bottles) to the complete lyrics of the "99 bottles of beer" ; song using just syntax-rules. Different bottle counts can be passed ; to the transformer by specifying tens and ones separately, e.g.: ; (bottles 2 3). (define-syntax verse (syntax-rules () ((_ x y z) `((,(+ (* x 10) y) bottles of beer on the wall) (,(+ (* x 10) y) bottles of beer) (take one down and pass it around) (,(+ -1 (* x 10) y) bottles of beer on the wall) ,@z)))) (define-syntax bottles (syntax-rules () ((_) (bottles 9 9)) ((_ 0 2) `((2 bottles of beer on the wall) (2 bottles of beer) (take one down and pass it around) (1 bottle of beer on the wall) ,@(bottles 0 1))) ((_ 0 1) `((1 bottle of beer on the wall) (1 bottle of beer) (take one down and pass it around) (0 bottles of beer on the wall) ,@(bottles 0 0))) ((_ 0 0) '((0 bottles of beer on the wall) (0 bottles of beer) (go to the store buy some more) (99 bottles of beer on the wall))) ((_ x 9) (verse x 9 (bottles x 8))) ((_ x 8) (verse x 8 (bottles x 7))) ((_ x 7) (verse x 7 (bottles x 6))) ((_ x 6) (verse x 6 (bottles x 5))) ((_ x 5) (verse x 5 (bottles x 4))) ((_ x 4) (verse x 4 (bottles x 3))) ((_ x 3) (verse x 3 (bottles x 2))) ((_ x 2) (verse x 2 (bottles x 1))) ((_ x 1) (verse x 1 (bottles x 0))) ((_ 9 0) (verse 9 0 (bottles 8 9))) ((_ 8 0) (verse 8 0 (bottles 7 9))) ((_ 7 0) (verse 7 0 (bottles 6 9))) ((_ 6 0) (verse 6 0 (bottles 5 9))) ((_ 5 0) (verse 5 0 (bottles 4 9))) ((_ 4 0) (verse 4 0 (bottles 3 9))) ((_ 3 0) (verse 3 0 (bottles 2 9))) ((_ 2 0) (verse 2 0 (bottles 1 9))) ((_ 1 0) (verse 1 0 (bottles 0 9)))))