RFC: Show symbols with a colon

[toivoh]

Currently, symbols show without a colon:

julia> :x
x

This patch changes it to

julia> :x
:x

print still produces the raw name when you need it, and thus string does as well.

I think this change would improve clarity. I put an RFC in the title because I wasn't sure if there's a reason that this hasn't been implemented already. Thoughts?

Btw, I built this patch on top of #1458, since I thought that one would be less controversial. If there's interest for a patch only changes show for symbols, I could fix that easily.

[johnmyleswhite]

I am also unaware of any problems this would cause, but, barring that, I think this change would make symbols more clear to newcomers. This style of showing is what Ruby does, for example.

[StefanKarpinski]

I've wanted this for a long time but @JeffBezanson had some objection, possibly the stringification business which t seems you've addressed here. So if he's cool with it, I'm all for. Thanks for doing this, btw.

[JeffBezanson]

My objection is this:

julia> quote f(:x,:y) end
quote   #  line 1:
    :f(:x, :y)
end

julia> quote f(x,y) end
quote   #  line 1:
    :f(:x, :y)
end

The syntax for calling f on x and y prints the same as the syntax for calling f on the symbols :x and :y.

[toivoh]

Is that a constructed julia output? Because with the code in this pull request I get

julia> quote f(:x,:y) end
quote   #  line 1:
    f(:x, :y)
end

julia> quote f(x,y) end
quote   #  line 1:
    f(x, y)
end

which seems pretty much ideal to me.

The reason that this works is that when passing an Expr to show, it will (already) put in appropriate quote markings
(like :( ... ) or turn begin ... end into quote ... end), and then invoke show_unquoted on the Expr. All printing of normal AST constructs will then be handled by recursive calls to show_unquoted. When it gets to the :x in f(:x, :y), on the other hand, that's represented with an expr(:quote, :x). show_unquoted shows the quote expr using the normal (quoted) entry point, and the quoted symbols print as quoted.

So, if it weren't for the distinction between show and show_unquoted, I would agree with you. I've really tried to be faithful to julia syntax in the AST printing code.

[JeffBezanson]

Ah, I got that output by applying only the change to show(io, s::Symbol).