[TxMt] Re: Defining a regular expression looking like a grammar

[Jacob Carlborg]

> On 21 Oct 2018, at 08:54, Allan Odgaard <mailinglist at textmate.org> wrote:
> 
> On 17 Oct 2018, at 17:36, Jacob Carlborg wrote:
> 
> This is exactly according to the specified grammar [3] and it seems to be working as expected. Not sure if the optional group workaround causes some performance implications.
> 
> This technique seems like it could be a viable alternative to supporting variables in the TextMate grammar as has been discussed before.
> 
> Just to be clear, you are talking about variables from the parsed language and highlighting them later in the scope, right?
> 
> So something like: let foo = 42 in … something_with foo … and here the latter instance of foo would be marked as a variable?
> 
No, I’m talking about having variables in the grammar with reusable regular expression snippets. Something like:

{
  patterns = (
    {
      name = 'meta.definition.class.d';
      match = 'class $identifier’; // the “identifier” variable referenced/interpolated
    }
  );
  repository = {
    variables = {
      identifier = '(\w+)';
    };
  };
}

In the above example “identifier” would be a variable that can be interpolated in other rules.

The above example would be one approach. Another approach to support variables is what I showed in my original post but using already existing features of regular expression.

{
  patterns = (
    {
      name = 'meta.definition.class.d';
      match = ‘\g<class_declaration>’; // this is standard regular expression syntax that works today in TextMate we just need somewhere to define “class_declaration"
    },
    {
      name = ‘meta.definition.struct.d’;
      match = ’struct\s+\g<identifier>’; // reusing the “identifier” sub expression in another pattern
    }
  );
  repository = {
    defines = '(?x) // here sub expressions can be defined which can later be used in “patterns"
      (?<class_declaration>class\s+\g<identifier>)
      (?<identifier>\w+)
    ‘;
  };
}

This is all about how one can write/implement a TextMate grammar. This approach would allow to write a TextMate grammar that closely follows a “real” grammar for a programming language, like a BNF grammar. I hope this makes it a bit more clear.

--
/Jacob Carlborg

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