From: "Haase, Konstantin" <Konstantin.Haase@...>
Date: 2011-11-07T20:02:37+09:00
Subject: [ruby-core:40812] Re: [ruby-trunk - Feature #5478] import Set into core, add syntax

I don't think it's impossible to parse. Ruby also manages to parse `p /a/m` as regexp rather than `p / a / m`.

Konstantin

On Nov 6, 2011, at 17:05 , George Koehler wrote:

> 
> Issue #5478 has been updated by George Koehler.
> 
> 
> =begin
> Ruby stdlib already has Set::[], a method that creates a literal set.
> 
> irb(main):001:0> require 'set'
> => true
> irb(main):002:0> Set[1, 2, 3]
> => #<Set: {1, 2, 3}>
> 
> The proposed syntax <1, 2, 3> might be impossible to parse, because it conflicts with < and > operators. Consider this example:
> 
> def c(*args); args.length; end
> 
> p c <1, 2, 3>
> 4
> 
> Current Ruby (with no set literal syntax) parses this example like so:
> 
> p(c() < 1, 2, (3 >
>                4))
> 
> If <1, 2, 3> became a set literal, then this example would become ambiguous. No parser would know whether this code has a set literal, or calls < and > operators.
> =end
> 
> ----------------------------------------
> Feature #5478: import Set into core, add syntax
> http://redmine.ruby-lang.org/issues/5478
> 
> Author: Konstantin Haase
> Status: Open
> Priority: Normal
> Assignee: 
> Category: 
> Target version: 3.0
> 
> 
> =begin
> A set is a central data structure. However, a lot of Ruby developers use arrays for situations where it would be more reasonable to use a set. One reason for that is that it is way easier to use Array then Set at the moment, another one is that developers are simply not aware it exists.
> 
> I propose moving Set from the stdlib to core and possibly add a syntax or a method on array for creating Set literals.
> 
> First class syntax suggestions:
> 
>    <1, 2, 3>  # might be tricky to parse
>    #[1, 2, 3] # would collide with comments
>    $[1, 2, 3]
>    ${1, 2, 3}
> 
> Method suggestions:
> 
>    ~[1, 2, 3]
>    +[1, 2, 3]
> 
> Whitespace separated String Sets could look like this:
> 
>    %w<foo bar blah> # creates an array at the moment 
>    #w[foo bar blah] # would collide with comments
>    $w[foo bar blah] # would collide with sending :[] to $w
>    $w{foo bar blah}
> 
>    ~%w[foo bar blah] # not really shorter than using an array with strings
>    +%w[foo bar balh] # not really shorter than using an array with strings
> 
> Maybe it's ok to not have a whitespace separated syntax, I'm just brainstorming here.
> 
> The issue with the method approach is that it would create an Array to send the message to first.
> 
> I favor the <1, 2, 3> syntax, possibly without the ability to create a whitespace separated version.
> 
> I'd be willing to work on a patch not only for MRI but also for JRuby and Rubinius if you would consider this to be useful.
> Although I would need help with the parser.
> =end
> 
> 
> 
> -- 
> http://redmine.ruby-lang.org
>