Syntax ambiguity when range is used in ternary operator

[AzamatB]

The following code produces unexpected output:

julia> true ? 1:3 : 4:7
1

of course, it can be fixed by adding braces:

julia> true ? (1:3) : (4:7)
1:3

However, I still think it should be deprecated for the same reason that
1.+2 was deprecated. Especially, in light of the fact that it produces erroneous output.

[ararslan]

This is actually expected, since ternaries are parsed more eagerly than ranges. You can see what's actually happening by inspecting the output of parse:

julia> parse("true ? 1:3 : 4:7")

WARNING: deprecated syntax "true ? 1:".
Use "true ? 1 :" instead.

WARNING: deprecated syntax "true ? 1 :3".
Use "true ? 1 : 3" instead.
:(if true
        1
    else
        3:4:7
    end)

That is, the precedence is (true ? 1 : (3:4:7)).

[AzamatB]

Which version is this? I don't get these warnings in 0.6.

[GregPlowman]

I'm not sure it's erroneous output, but rather a case of parsing precedence.
Presumably it is parsed as:
true ? 1 : (3:4:7)
which is valid syntax.

[ararslan]

The output I posted was from the current master, but the parsing is the same across all Julia versions (or at least 0.3-0.7—I don't have 0.2 or lower installed). The deprecation warnings are new though, recent 0.7.

[AzamatB]

Can you confirm that these warnings don't show up in 0.6?

[StefanKarpinski]

Yes – as a side effect of requiring space after ? in ternary on master, we've also required spaces around the : in ternary, so this is now already a warning, forcing parens or spaces matching.