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@lezer/lr

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@lezer/lr

Incremental parser

  • 0.15.8
  • Source
  • npm
  • Socket score

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1
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What is @lezer/lr?

@lezer/lr is a library for building efficient parsers in JavaScript. It is part of the Lezer parser system, which is designed to be fast, flexible, and easy to use. The library provides tools to define grammars, build parsers, and work with syntax trees.

What are @lezer/lr's main functionalities?

Defining a Grammar

This feature allows you to define a grammar for your language. The code sample demonstrates how to define a simple grammar for a language that supports print statements with string literals.

const {parser} = require('@lezer/lr');
const {buildParser} = require('@lezer/generator');

const grammar = `
@top Program { statement* }

statement { "print" String }
String { "\"" (!"\"")* "\"" }
`;

const myParser = buildParser(grammar);
console.log(myParser.parse('print "Hello, World!"'));

Parsing Input

This feature allows you to parse input strings according to the defined grammar. The code sample shows how to parse a simple print statement and output the resulting syntax tree.

const {parser} = require('@lezer/lr');
const {buildParser} = require('@lezer/generator');

const grammar = `
@top Program { statement* }

statement { "print" String }
String { "\"" (!"\"")* "\"" }
`;

const myParser = buildParser(grammar);
const tree = myParser.parse('print "Hello, World!"');
console.log(tree);

Working with Syntax Trees

This feature allows you to work with and traverse syntax trees generated by the parser. The code sample demonstrates how to recursively print the structure of a syntax tree.

const {parser} = require('@lezer/lr');
const {buildParser} = require('@lezer/generator');

const grammar = `
@top Program { statement* }

statement { "print" String }
String { "\"" (!"\"")* "\"" }
`;

const myParser = buildParser(grammar);
const tree = myParser.parse('print "Hello, World!"');

function printTree(node, indent = 0) {
  console.log(' '.repeat(indent) + node.type.name);
  for (let child of node.children) {
    printTree(child, indent + 2);
  }
}

printTree(tree.topNode);

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Package last updated on 04 Feb 2022

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