@lezer/lr

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);