I just got around to watching Clojure TV on sequences, which I guess I should have done earlier, but I guess I was too lazy — thanks, I’m here all week.
Ok — since clearly, day 20 is going to be about Clojure Day in Northampton, I only have two days to explore more of clojure. I haven’t even gotten to multimethods, which are very cool, but pretty simple to understand. I want to keep working with macros.
The hardest thing about thinking about macros is that not using a language that has one, I haven’t started to think in macros yet. Kind of reminds me of Clint Eastwood in Firefox who has to keep remembering to think in Russian in order to fly his stolen super-secret Soviet jet.
Ok, since I think in OO, let me try to do some OO in clojure via macros — maybe I get to use multimethods after all (let’s hobble them with conventional OO polymorphism)
(defclass rect
(defctor (fn [w h] (setprop w) (setprop h) ))
(defmeth area (fn [] (* w h)))
)
(defclass circle
(defctor (fn [r] (setprop r)))
(defmeth area (fn [] (* r r (. Math PI))))
)
I want that to turn into
(defn rect [w h] {:type :rect :w w :h h})
(defmulti area :type)
(defmethod area :rect [r]
(* (:w r) (:h r)))
(defn circle [r] {:type :circle :r r})
(defmulti area :type)
(defmethod area :circle [c]
(* (. Math PI) (* (:r c) (:r c))))
I’m not even sure this is possible — I just checked to see if it’s legal to defmulti the same name, and it’s not really because it kills the definition for rect. Luckily, I have a precedent to fall back on — in Java/C# style OO, area is only polymorphic if it came from a superclass. I can change the class structure to this:
(defclass shape
(defabstractmeth area)
)
(defclass rect :extends shape
(defctor (fn [w h] (setprop w) (setprop h) ))
(defmeth area (fn [] (* w h)))
)
(defclass circle :extends shape
(defctor (fn [r] (setprop r)))
(defmeth area (fn [] (* r r (. Math PI))))
)
This is so ugly, I don’t even know if I want to go through with this. I’ll try for tomorrow.