Saturday, January 17, 2015

Hy flow macros.

While working on my new web framework Horn, written in Hy of course, I found myself lacking some flow controls. So I just wrote some macros!

;; Additional flow macros

(defmacro/g! guard [&rest args]
  (setv g!cond (car args))
  (setv g!body (car (cdr args)))
  (setv g!rest (cdr (cdr args)))
  (if g!rest
  `(if ~g!cond
       (guard ~@g!rest))
  `(if ~g!cond

(defmacro/g! switch [variable &rest args]
  (setv g!comp (car args))
  (setv g!body (car (cdr args)))
  (setv g!rest (cdr (cdr args)))
  (setv g!cond `(~(car g!comp) ~variable ~@(cdr g!comp)))
  (if g!rest
      (if (cdr g!rest)
        `(if ~g!cond ~g!body (switch ~variable ~@g!rest))
        `(if  ~g!cond ~g!body ~@g!rest))
      `(if  ~g!cond ~g!body)))

As you can see, switch is basically just a guard statement, but with the original variable playing a role in every comparison, and with an additional else clause (since guard can only do that with a True).
It's amazing how powerful macros are, and I'm really starting to like what I can do with them. I've already submitted these to hy.contrib, and I hope they get accepted. Try some Hy!

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