While Loop Macro in DrRacket

Question

I am trying to create a macro for while loop in DrRacket. Here is what I wrote:

(require mzlib/defmacro)

(define-macro my-while
  (lambda (condition  body)
         


        

Answer 1

Ouch:

1. Using this style of while loop encourages excessive use of imperative programming.
2. Using define-macro creates unhygienic macros, which is a nightmare in Scheme.

While I don't encourage writing an imperative-style loop macro, for your reference, here's a non-define-macro version of the same macro:

(define-syntax-rule (my-while condition body ...)
  (let loop ()
    (when condition
      body ...
      (loop))))

It uses syntax-rules, which creates hygienic macros, and is much, much easier to read than what you have.

---

Now, for the actual answer for your question, first, let's write your original macro out in a more readable way:

(define-macro my-while
  (lambda (condition body)
    `(local ((define (while-loop)
               (if ,condition
                   (,body (while-loop))
                   (void))))
       (while-loop))))

Once you write it out this way, you can see where the real problem is: in the (,body (while-loop)) line, which should instead have been (begin ,body (while-loop)).