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Re: Questions about tree-sitter

From: Yuan Fu
Subject: Re: Questions about tree-sitter
Date: Tue, 5 Sep 2023 21:07:58 -0700

> On Aug 30, 2023, at 4:28 AM, Augustin Chéneau (BTuin) <btuin@mailo.com> wrote:
> Le 30/08/2023 à 09:03, Yuan Fu a écrit :
>>> On Aug 29, 2023, at 2:26 PM, Augustin Chéneau (BTuin) <btuin@mailo.com> 
>>> wrote:
>>> Hello,
>>> I have a few questions about tree-sitter.
>>> I'm currently developing a grammar for GNU Bison alongside a tree-sitter
>>> major mode, it's a work in progress.  The grammar is here:
>>> <https://gitlab.com/btuin2/tree-sitter-bison>, still incomplete but so
>>> far able to parse simple files, and the major mode prototype is
>>> attached to this message.
>>> So, the questions:
>>> 1. Is there a way to reload a grammar?
>>> Emacs is pretty nice as a playground for testing grammars, but once a
>>> grammar is loaded, it won't be loaded again until Emacs restarts (as far
>>> as I know).
>>> Is it possible to reload a grammar after modifying it?
>> No, and it’s probably not easy to implement either, since unloading the 
>> grammar would require Emacs to purge/invalid all the node/query/parsers 
>> using that grammar.
>>> 2. How to mix multiple languages?
>>> It would be very useful for Bison since its mixed with C or other languages.
>>> According to the documentation I need to use the function
>>> `treesit-range-rules` to set the variable `treesit-range-settings`, but
>>> it seems to have no effect.  The language in the selected nodes doesn't
>>> change (as attested by `(treesit-language-at (point))`).
>>> I did it that way (extracted from the attachment):
>>> (setq-local treesit-range-settings
>>>      (treesit-range-rules
>>>       :embed 'c
>>>       :host 'bison
>>>       '((undelimited_code_block) @capture)))
>>> Am I missing something?
>> The ranges are set correctly, actually. But the C parse sees all those 
>> blocks stitched together as a whole, rather than individual blocks, and the 
>> code it sees is obviously not syntactically correct.
>> We should really work on supporting isolated ranges, there has been multiple 
>> requests for it. I’ll try to work on that.
>>> 3. Is it possible to trigger a hook when a node is modified?
>>> Since Bison supports multiple languages (C, C++, Java and D), I'd like
>>> to watch the declaration "%language LANGUAGE" to change the embedded
>>> language when needed.
>>> Is there a way to do that?
>> treesit-parser-add-notifier might be what you want.
>> Yuan
> I see.  Thank you for your answers and for your great work on tree-sitter!

I added local parser support to master. If everything goes right, you just need 
to add a :local t flag in treesit-range-rules. Check out the modified 
bision-ts-mode.el that I hacked up for an example. BTW, it’s vital that you 
define treesit-language-at-point-function for a multi-language mode.


Attachment: bison-ts-mode.el
Description: Binary data

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