LSP tries to understand code at a semantic level. It not just looks at one file, but also the entire project. It analyses projects and code in a way such that it can offer definition, references, and completions that are accurate.

Tree-sitter looks at one file at a time and provides incremental and quick feedback from that file.

Compiler

It doesn't know about types, or package.

It only knows the text.

Interpreter

There is nothing running. It is just a library to interact with text.

Tree-sitter IS

Parser generator tool

You can write a grammar, which can be transformed into a parser. Parser is loaded by application embedding tree-sitter and can be used inside the application.

Incremental parsing library

Parser automatically get this incremental and error recovering part of that grammar. No need to write that as grammar making process.

Query engine

A framework to:

• Generate a syntax tree
• Ask questions about the tree

Why Tree-sitter in an Editor?

Incremental

Text gets added and removed character by character. It is preferred for the parser to not have to recompute the tree everytime we type.

Error Recovery

As you're writing a particular line of code, it is broken until you finish the sentence or phrase. You don't want the parser to throw its hands up as this is understood. You want to find minimal amount of error and keep it local, ensuring the rest of the file is highlighted.

Queries

Ask questions to the tree and retrieve that answer for editor or other applications to perform useful tasks with this information.

How Does Tree-Sitter Work?

Underlying Stack: grammar.js

Grammars are written in "JavaScript".

• JavaScript-like DSL in grammar.jsfile
• These are compiled to a parser.c via the tree-sitter cli.

Underlying Stack: Results of grammar.js

|-src
|  |- grammar.json
|  |- node-types.json
|  |- parser.c
|  |- scanner.c 
|  |- tree_sitter
|  |   |- parser.h

Why C?

Only dependencies is a C Compiler. Most build systems have this.

Good Foreign Function Interface story for lots of languages with C. Easy to embed tree-sitter into other applications and access them with bindings.

This makes tree-sitter very portable.

Compile C Code to Shared Library

cc -o ./build/parser.so -I./src src/parser.c src/scanner.c -shared -Os -fPIC

Gets you a parser.so

Shared Library

You can load that shared library as a parser inside of some applications that support tree-sitter.

What is Tree-sitter Used For (in an Editor)?

• Highlighting
  • Embedding languages
• Indenting
• Structural editing
  • Text objects (daf --> 'D'elete 'A'round 'F'unction)
  • Selection
  • Move
• Code context
• Folding
• ...

What is Tree-sitter Used For (outside Editor)?

• Code Analysis
• Code Linter
• Code Highlighting