Add Clojure tagged literals or similar

[gilch]

Our reader macros have capabilities similar to Clojure's tagged literals, but Hy's are limited to a single character after the dispatch character #. In Clojure, it can be an arbitrary symbol after the #. One-character macros make sense for something that gets used all the time, or for DSLs where something has to be repeated a lot. But for general user uses, it could be nicer to use a more descriptive name.

I'm not sure how hard it would be to adapt Hy's reader macros to read a symbol instead of a character.

[Foxboron]

That would be very trivial actually. We decided on one character when i wrote it a looonngg time ago.... maybe @olasd still remembers why.

[gilch]

I can think of one possible reason to restrict it to one character. Say we have a simple an example reader macro:

(defreader % [x] `(print '~x))

Then, with the current restriction, you can apply the reader macro directly to a symbol, like this:

=> #%Hy!
Hy_bang

But if we allowed longer symbols, Hy would try to look up the %Hy! reader macro instead. This is easy to fix. Clojure simply requires a space in such cases, and Hy already allows this:

=> #% Hy!
Hy_bang

It's probably good style to use a space when applying reader macros to symbols anyway, but what if we applied it to a number instead?

=> #%42
42

Again, Hy would look for the %42 reader macro. I think this feels nicer without the space, but I still think the change would be worth it.