This is normal Ruby semantics.
Consider:

method_name another_method do

end

In this case, the "do" is bound to method_name. Now consider:

method_name another_method {

}

In this case, the {} is bound to another_method. Proc.new is just a normal
method, so the above applies.

-- Yehuda


On Fri, Oct 16, 2009 at 10:48 AM, Iņaki Baz Castillo <ibc@aliax.net> wrote:

>
> Hi, the following works:
>
>
> 1       ::Rack::Builder.new do
> 2               map "/" do
> 3                       run Proc.new { |env|
> 4                               [ 404, {"Content-Type" => "text/plain"}),
> [""] ]
> 5                       }
> 6               end
> 7       end
>
>
> but the following gives an error:
>
> 1       ::Rack::Builder.new do
> 2               map "/" do
> 3                       run Proc.new do |env|
> 4                               [ 404, {"Content-Type" => "text/plain"}),
> [""] ]
> 5                       end
> 6               end
> 7       end
>
> /home/me/myfile.rb:3:in `new': tried to create Proc object without a block
> (ArgumentError)
> from /home/me/myfile.rb:3:in `block (2 levels) in core'
> from
> /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `instance_eval'
> from
> /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `initialize'
> from
> /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:46:in
> `new'
> from
> /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:46:in
> `map'
> from /root/svn_local_copies/OpenXDMS/trunk/lib/rack/core.rb:46:in `block in
> core'
> from
> /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `instance_eval'
> from
> /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `initialize'
> from /home/me/myfile.rb:1:in `new'
> ...
>
>
> It fails in ruby 1.8 and 1.9. Why cannot I use "do-end" syntax for a block
> instead of "{ }". Of course, Proc.new does allow "do-end" syntax, so I
> wonder
> if this issue has something to do with Rack itself.
>
>
> Thanks.
>
>
> --
> Iņaki Baz Castillo <ibc@aliax.net>
>



-- 
Yehuda Katz
Developer | Engine Yard
(ph) 718.877.1325