[jonathanyc]

The query language is definitely underdocumented. In case it helps you, what helped me was realizing it’s basically a funky pattern language, à la the match pattern sublanguages in OCaml/Haskell/Rust.

But the syntax for variable binding is idiosyncratic and the opposite of normal pattern languages. Writing “x” doesn’t bind the thing at the position to the variable x; instead, you have to write e.g. foo @x to bind x to the child of type foo. Insanely, some Scheme dialects use @ with the exact opposite semantics!! There’s also a bizarre # syntax for conditionals and statements.

Honestly there isn’t really an excuse for how weird they made the pattern syntax given that people have spent decades working on pattern matching for everything from XML to objects (even respecting abstraction!). I’ve slowly been souring on treesitter in general, but paraphrasing Stroustrup: there are things people complain about, and then there are things nobody uses.

[ckolkey]

Its just a Scheme dialect. A bit odd, but not crazy.

[jonathanyc]

Not really. It uses S-expressions but Scheme pattern matching is totally different. The most common Scheme pattern matching syntax is basically the same as pattern matching in any other language: x means “bind the value at this position to x”, not “the child node of type”. See: https://www.gnu.org/software/guile/manual/html_node/Pattern-... or syntax-rules.

It’s as much a Scheme dialect as WASM’s S-expression form is a Scheme dialect.

Treesitter’s query syntax is slightly understandable in the sense that having x match a node among siblings of type x works well for extracting values out of sibling lists. Most conventional pattern syntaxes struggle with this, e.g. how do you match the string “foo” inside of a list of strings in OCaml or Rust without leaving the match expression and resorting to a loop?

But you could imagine a syntax-rules like use of ellipses …. There’s also a more powerful pattern syntax someone worked on for implementing Scheme-like macros in non-S-expression based languages whose name escapes me right now.