On 26.02.2009, at 01:51, Rich Hickey wrote:
> You raise interesting issues and I'd like to explore them further. I'm
> not sure the issues you have with type-tag-or-class dispatch are all
> that prohibitive. In any case, I've added a type function that returns
> the :type metadata or the class if none:
Thanks, that helps a lot! With a built-in universal dispatching
function, most of my problems should be solved. Another useful
function to have would be
(defn type-instance?
"Evaluates x and tests if it is an instance of the type or class t.
Returns true or false"
[t x]
(identical? t (type x)))
for type-based dispatching inside a function.
> I'm not sure the mechanism you are using (actual Class types) allows
> for any more overloading - Class is a single slot too, after all.
True, but the number of classes is not limited. Java programmers can
live with a single class hierarchy, so it can't be too bad. But
Clojure's hierarchies are definitely more flexible.
> A bigger problem with the mechanism you've chosen is its dependence on
> some implementation details. I haven't promised, e.g. that every fn
> generates a unique class type.
I know, but as I said, my current implementation is just a proof of
concept. It is not viable for production use for a variety of
reasons. I was planning to replace it by something based on gen-class
and proxy, but I will first try to get away with the new type function.
Konrad.
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