On Feb 26, 2009, at 1:51, 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:
>
> user=> (type #^{:type ::Fred} [1 2 3])
> :user/Fred
>
> user=> (type "foo")
> java.lang.String
>
> which should help people standardize.
One inconvenience I noticed with types based on meta-data tags is
that the type information does not participate in equality tests.
This means I have to include the type information once again in the
value itself if I want to make sure that no other type's value
accidentally compare as identical to mine.
> If you want to multiplex multimethods for your ADT type, you can just
> define a single :type ::ADT, and then sub-dispatch on e.g. :adt-type.
That's not even necessary: I add a derive clause from ::adt to each
of my data types and implement multimethods such as print-method
for ::adt.
Konrad.
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