Question

I am working on a macro, I am trying to figure out how to avoid expansion of certain forms, take the following and macro for example,

(defmacro and
  ([] true)
  ([x] x)
  ([x & next]
   `(let [and# ~x]
      (if and# (and ~@next) and#))))

When expanded,

(mexpand-all '(and 1 2 3))

becomes,

(let* [and__973__auto__ 1]
      (if and__973__auto__
        (let* [and__973__auto__ 2]
              (if and__973__auto__ 3 and__973__auto__))
        and__973__auto__))

In this case what I need to do is stop let from expanding into let*.

Answer 1

Recursive macro-expansion works by repeatedly expanding the form until there is no macro to expand. That means that if you want to recursively expand a macro, but ignore certain forms, you’ll have to either code your own custom expander, or find someone else’s.

Here’s a quick example:

(defn my-expander [form]
    (cond (not (list? form)) (mexpand-1 form)
        (= (first form) 'let) form
           :else (map my-expander (mexpand-1 form))))

Please forgive me if I made any mistakes. I’m much stronger with Scheme and CL than Clojure.

–Edit–
Note that the above function will not expand the subforms of a let statement, either.