Expr should use quotable symbols only

[stevengj]

Currently, Expr sometimes requires LISPy symbols that are not quotable in Julia, e.g.:

julia> :((Int=>Symbol)[1 => :ok, 2=>:no])
:($(expr(:typed-dict, :(Int=>Symbol), :(1=>:ok), :(2=>:no)))) 

That means that one needs to use expr(symbol("typed-dict"), ...) or similar escaping mechanisms to form such expressions manually (e.g. in macros). It would be desirable to use quotable identifiers (e.g. :typed_dict) in such cases instead.

Other examples include :typed-dict-comprehension, :dict-comprehension, and :typed-comprehension. I'm not sure if there are any others.

For backwards compatibility, I suppose one could allow either the hyphenated form or the underscored form (but use the latter by default).

[mlubin]

+1. Backward compatibility may not be so important for this if it goes into 0.2.

[JeffBezanson]

Agree.