请在Scheme中重构我的宏

Question

我正在学习卫生,我试图在Scheme中进行简单的for循环.我想支持三种结构,如下例所示

(for i = 1 : (< i 4) : (++ i)
  (printf "Multiplication Table for ~s\n" i)
  (for j = 1 to 5
    (printf "~s * ~s = ~s\n" i j (* i j))))

我想也支持带有这样的过滤器的循环:

(for k = 1 : 10 : (list even? (?(x) (> x 4))) : (++ k)
  (print k))

我有这个,但我可以看到很多重复.请帮我删除冗余.

(define-syntax for
  (syntax-rules (= to :)
    [(for x = initial : final : conditions : increment body ...)
     (letrec ([loop (?(x)
                      (when (<= x final)
                        (when (andmap (?(condition) (condition x)) conditions)
                          body ...)
                        (loop increment)))])
       (loop initial))]
    [(for x = initial : condition : increment body ...)
     (letrec ([loop (?(x)
                      (when condition
                        body ...
                        (loop increment)))])
       (loop initial))]
    [(for x = initial to n body)
     (for x = initial : (<= x n) : (+ x 1) body)]))

Answer 1

我在这里看不到很多重复.只有一个.它可以这样删除:

(define-syntax for
  (syntax-rules (= to :)
    [(for x = initial : final : conditions : increment body ...)
     (for x = initial : (<= x final): increment
          (when (andmap (?(condition) (condition x)) conditions)
            body ...))]
    [(for x = initial : condition : increment body ...)
     (letrec ([loop (?(x)
                      (when condition
                        body ...
                        (loop increment)))])
       (loop initial))]
    [(for x = initial to n body)
     (for x = initial : (<= x n) : (+ x 1) body)]))