Re: Plug treesit.el into other emacs constructs

[Theodor Thornhill]

On 14 December 2022 15:01:55 CET, Stefan Monnier <monnier@iro.umontreal.ca> 
wrote:
>> I would argue that the purpose of forward-sexp is to move over items in
>> a list.
>
>There are different ways to look at it.  In the Lisp context where it
>emerged, we only have "identifiers" and "parenthesized thingies", so
>that doesn't give much guidance about what to do in-between.
>
>The semantics I chose for SMIE is what I found to be closest to
>past practice.
>
>> Always going for the smallest subtree doesn’t seem to align with it.
>> Take that example above, going across the smallest subtree means
>> moving over X, then moving over “.”,
>
>No: when you're left of ".", as in "(X|.y(z), alpha)", the SMIE
>semantics of `forward-sexp` moves over ".y(z)", i.e. to
>"(X.y(z)|, alpha)"
>
>> that doesn’t feel like what forward-sexp should do to me.
>
>Indeed, moving just over "." would be very far from my understanding of
>what `forward-sexp` intends to do.
>
>> You mean in the following code
>>
>> int a = 0[1];
>> int b = 1;[2]
>>
>> Forward-sexp would move [1] to [2]?
>
>No, SMIE's `forward-sexp` moves from
>
>    int a = 0|;
>    int b = 1;
>
>to
>
>    int a = 0;
>    int b = 1|;
>
>[ You can try it by installing Tuareg and moving around in an OCaml
>  file, for example.  ]
>
>and when moving backward it moves from
>
>    int a = 0;
>    int b = 1;|
>
>to
>
>    int a = 0;|
>    int b = 1;
>
>> But if we move over the smallest
>> subtree, I’d imagine it only move across the semicolon after [1].
>

Doesn't this look like forward-sentence?


>In my view ";" is not a substree.  It's the node of a substree.
>We can't actually move over a proper subtree in that case because there
>is no substree whose left boundary starts right before the ";", so the
>closest is to move over the ";" *plus* its right child.
>
>> Even if it moves from [1] to [2], needing to adjust point feels very
>> inconvenient to me, at least I wouldn’t want to use something
>> like that.
>
>Moving point is the way to tell SMIE's `forward-sexp` which level of the tree
>we want to navigate.  I don't believe Emacs can reliably guess the right
>level, and I don't believe choosing an arbitrary level for the users
>serves them best either.  I can imagine other ways to specify the
>intended tree level, tho: maybe we could have a kind of prefix command
>for that.  E.g. a new command that would work a bit like `C-M-u` (or its
>younger sibling `expand-region`) but would only affect the next sexp
>command instead.
>
>> I want to type a single binding and move to where I want, and
>> type that binding multiple times to move multiple steps.
>
>I don't think a single binding can always jump to where you want.
>That would require magic :-)
>
>But yes, SMIE's `forward-sexp` does work well when repeated to jump over
>N instructions, it was indeed an important design goal.
>
>
>        Stefan
>