examples
defining a special form as a procedure
- consider this procedure (“x unless c, in which case y”)
(define (unless c x y) (if c y x))
- application with Scheme rules
(unless #t 3 4) ==> 4
(unless #t (1 1) 4) fails
- application with lazy rules
(unless #t 3 4) ==> 4
(unless #t (1 1) 4) ==> 4