bug#15594: trunk r114639: * lisp/progmodes/ruby-mode.el (ruby-smie-grammar): Add rule for paren-free

[Dmitry Gutov <dgutov@yandex.ru>]

On 15.10.2013 07:31, Stefan Monnier wrote:
>> How would that look?
>> (unless (member (save-excursion (ruby-smie--forward-token) '("]" "}" "end"
>> "+" "-" "?" ":" ...)))
>
> (looking-at "\\s)\\|\\s.") ?

I guess this is better, but it has both false negatives (unary operators 
like -, ~ and !) and false positives (all non-opener keywords).

>> Or should the check be more like "is the next token in `ruby-smie-grammar',
>> and if yes, is its left priority more than ' @ 's right priority"?
>
> Calling ruby-smie--forward-token is a bit dangerous since that function
> might itself be called from ruby-smie--forward-token.  It might work,
> but you'll have to think hard about why an inf-loop is not possible.

Hopefully because both `ruby-smie--forward-token' and 
`ruby-smie--backward-token' would only call `ruby-smie--forward-token', 
and only when (> pos (point)), IOW there has to be some whitespace 
skipping done between the recursive calls.

>> You've probably already found this, but on the off chance you haven't,
>> here's its syntax in (incomplete, somewhat outdated, etc) BNF form:
>> http://www.cse.buffalo.edu/~regan/cse305/RubyBNF.pdf
>
> Please add this URL in a comment somewhere near ruby-smie-grammar (for
> example).

Done.

> Getting `foo' and `bar' aligned is just a matter of adding && to the set
> of infix operators (i.e. completing the table of infix operators).
> Getting `bar' to be indented one more than `foo' here but not in other
> cases of "foo && \n bar" would require more work.

Ok, let's go with the former for now.