[grammarians] do/end vs braces

[mental@rydia.net]

Quoting Joe Van Dyk <joevandyk at gmail.com>:

> 5.times { |i| puts i }
>
> 5.times do |i|
>   puts i
> end

> Generally people save do .. end for multiline stuff.  Don't think
> there's a difference in speed.

I can promise there's no speed difference.  They both parse to the
same thing:

 (iter
   (call
     (lit #<5>) times)
   (dasgn_curr i)
   (fcall puts
     (array
       (dvar i))))

 (iter
   (call
     (lit #<5>) times)
   (dasgn_curr i)
   (fcall puts
     (array
       (dvar i))))

However, {} and do...end are not totally interchangable as syntax.
These are all equivalent:

 obj.meth( 1, 2 ) { |i|
   puts i
 }

 obj.meth( 1, 2 ) do |i|
  puts i
 end

 obj.meth 1, 2 do |i|
   puts i
 end

But this will net you a parse error ('2' is not a valid method
name):

 obj.meth 1, 2 { |i|
   puts i
 }

And these two parse equivalently:

 obj.meth 1, zog { |i|
   puts i
 }

 obj.meth( 1, zog { |i| puts i } )

Think of {} as being more "clingy" than do...end.

Basically, {} has higher precedence than do...end, just as (among
otherwise equivalent operators) && has higher precedence than
'and', and || has higher precedence than 'or'.

I'm sure Ter hates Ruby now. :)

-mental