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Re: How to add pseudo vector types

From: Yuan Fu
Subject: Re: How to add pseudo vector types
Date: Mon, 26 Jul 2021 13:09:13 -0400

>>> Once again, we are talking about the function used by TS to read
>>> buffer text.  Not about the parser or its caller.  Low-level code,
>>> which knows nothing about the context, should never look beyond the
>>> restriction.
>> It doesn’t harm for tree-sitter to see the rest of the buffer, it doesn’t 
>> modify anything, all it does it reading the text. OTOH, restricting 
>> tree-sitter to the bounds of narrows adds complexity for no benefit (as far 
>> as I can see).
> Which complexity does it add?  You just compare with BEGV_BYTE instead
> of BEG_BYTE etc.

We need to “delete” the hidden text and “re-insert” when we widen the buffer. 
I’ll try to make it a no-op as long as we remember to widen before calling 
tree-sitter to parse anything.

> If we let TS look where it wants, we will lose the ability to restrict
> it to a certain part of the buffer text.  This is needed at least for
> some specialized modes, and is generally desirable, as it gives Lisp
> programs an easy way to impose such restrictions whenever they need.

Tree-sitter lets you set ranges for a parser to limit it self within, in order 
to support multi-language files.

>> Maybe narrowing is the context that low level code should ignore
> No other code in Emacs does, and for a good reason.
>> The only benefit that I can think of is “we firmly adhere to the ‘contract’ 
>> that no one can look beyond the narrowed region”, but is it a good contract? 
>> Is there really a contract in the first place?
> It served us very well until now, so yes, I think it's a good
> contract.
>> IMO, narrowing acts like masking tapes over the rest of the buffer, so that 
>> user edits like re-replace wouldn’t spill out. Demanding everything in Emacs 
>> to not have access to the rest of the buffer is dogmatic (in the sense that 
>> it is too rigid and is simply following the doctrine blindly). 
> Again, this "dogma" is used and adhered everywhere else in Emacs by
> such low-level code.

Ok. I trust you to know better than I do.


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