Parsimmon is a small, elegant parser combinator library for JavaScript and Node.js.
Basic Example
const P = require('parsimmon');
// Create a parser matching one or more lowercase letters
const word = P.regexp(/[a-z]+/);
const result = word.parse('hello');
// => { status: true, value: 'hello' }
Atomic Parsers
P.string('function'); // Exact string literal
P.regexp(/[0-9]+/); // Regular expression match
P.oneOf('abc'); // Single character matching 'a', 'b', or 'c'
P.whitespace; // One or more whitespace characters
P.optWhitespace; // Zero or more whitespace characters
P.eof; // End of input stream
Combinators
// Sequence: matches all parsers in exact order
P.seq(P.string('('), P.number, P.string(')'));
// Alternatives: matches first successful parser
P.alt(P.string('true'), P.string('false'));
// or using .or():
a.or(b);
// Delimited / Separated lists
P.sepBy(P.number, P.string(',')); // Comma-separated numbers (zero or more)
P.sepBy1(P.number, P.string(',')); // Comma-separated numbers (at least one)
// Repetition
a.many(); // 0 or more
a.atLeast(1); // 1 or more
a.times(3); // Exactly 3 times
a.times(1, 4); // Between 1 and 4 times
// Discarding tokens
a.skip(P.string(';')); // Parses 'a', matches ';', returns only 'a'
Transforming Output (map)
const arithmeticExpr = P.seq(
P.digits.map(Number),
P.oneOf('+-*/').trim(P.optWhitespace),
P.digits.map(Number)
).map(([left, operator, right]) => ({
type: 'BinaryExpression',
operator,
left,
right
}));
arithmeticExpr.parse('10 + 20');
/*
{
status: true,
value: { type: 'BinaryExpression', operator: '+', left: 10, right: 20 }
}
*/