@lezer/common

What is @lezer/common?

The @lezer/common package is part of the Lezer project, which provides a robust, performance-focused parsing system. This particular package includes common utilities and types that are used across different parts of the Lezer ecosystem. It's designed to support the creation and manipulation of syntax trees, offering tools for parsing, analyzing, and transforming text.

What are @lezer/common's main functionalities?

Syntax Tree Navigation

This feature allows for navigating through a syntax tree. The code sample demonstrates how to create a cursor from a syntax tree and iterate over its nodes, printing the name of each node's type. This is useful for analyzing or transforming the structure of parsed documents.

let cursor = tree.cursor();
while(cursor.next()) {
  console.log(cursor.node.type.name);
}

Tree Fragment Reuse

Enables efficient parsing by reusing parts of an old syntax tree. The code shows how to apply changes to an array of tree fragments and then use these fragments to assist in parsing a new tree. This significantly improves performance when making incremental updates to a document.

let fragment = TreeFragment.applyChanges(fragments, changes);
let newTree = parser.parse({fragments: [fragment]});

Syntax Node Access

Facilitates direct access to specific nodes within a syntax tree based on position. The example code retrieves a node at a given position (5) and logs its name and the range it spans. This is particularly useful for pinpointing elements in a document for further inspection or modification.

let node = tree.resolve(5);
console.log(node.name, node.from, node.to);

Other packages similar to @lezer/common

chevrotain

Chevrotain is a fast and feature-rich parser building toolkit for JavaScript. Unlike @lezer/common, which is part of a specific parsing system, Chevrotain provides a more general toolkit for building parsers from scratch. It offers a higher level of customization but might require more setup for specific tasks.

nearley

Nearley is a simple, fast, and powerful parsing toolkit for JavaScript. It is designed to be flexible and easy to use, supporting a wide range of grammars. Compared to @lezer/common, Nearley focuses more on the grammar and less on the manipulation of syntax trees, making it a good choice for projects where grammar is a primary concern.

pegjs

PEG.js is a parser generator for JavaScript based on the Parsing Expression Grammar (PEG) syntax. It generates parsers with a focus on performance and error reporting. While PEG.js emphasizes the generation of parsers from grammars, @lezer/common is part of a system that includes predefined parsers and utilities for working with syntax trees.

README

@lezer/common

[ WEBSITE | ISSUES | FORUM | CHANGELOG ]

Lezer is an incremental parser system intended for use in an editor or similar system.

@lezer/common provides the syntax tree data structure and parser abstractions for Lezer parsers.

Its programming interface is documented on the website.

This code is licensed under an MIT license.

Changelog

0.15.12 (2022-03-18)

Bug fixes

Work around a TypeScript issue that caused it to infer return type any for resolve and resolveInner.

Fix a bug in incremental mixed-language parsing where it could incorrectly add a parse range twice, causing a crash in the inner parser.