[TxMt] Re: formal definition of scope selector syntax?

[Allan Odgaard]

On 25 Jun 2008, at 21:07, Matt Neuburg wrote:

> In the Help for TextMate, the following are given as examples of legal
> selectors (with explanations of what they mean / match):
> [...]
> Then, in a blog entry
> (http://blog.macromates.com/2005/introduction-to-scopes/),  
> additional info
> is given:
>
> (a | b) & c - d
>
> I find that last one incoherent; I don't get where the pieces are or  
> how the
> operators here fit, priority-wise, with the previously given  
> operators. For
> example, which of the selectors given in the first list would be a  
> legal
> substitute for "b" here? And conversely, for which expressions in  
> the first
> list of legal selectors, if any, could this expression be substituted?
>
> So, my question is: Can I somewhere get a formal coherent definition  
> of the
> rules of selector syntax?

I’ll see if I can’t add a BNF section to the manual. I won’t be  
online for an unknown amount of time, so not sure when I will push this.

As for your concrete question, in the last example you quote, a, b, c,  
and d can all be scope selectors of the form given in the manual  
section 13.1 or 13.2 (13.1 being a subset of 13.2).

So scopes are matched literally (e.g. “string”). These can form a  
“descendent selector” (13.2) e.g. “source.ruby string”, and for  
descendent selectors one can take the union (| or ,), the intersection  
(&), or the asymmetric difference (-).

As for the exact precedence of these operators, I’ll have to check  
the grammar in the source, but one can also group with parenthesis.  
The reason though that both , and | can be used for union is that ,  
was introduced long before the other operators (mimics CSS syntax), so  
when & was added, I felt that there should be | and | has higher  
precedence than , it is the operator with lowest precedence, so e.g.:

     a - b | c & d, e - f | g & h ⇔ (a - b | c & d), (e - f | g & h)

A bit like | versus || in C.