Pros of PEG.js

• Generates standalone parsers, allowing for easier distribution and integration
• Provides a more declarative syntax for defining grammars
• Offers built-in error reporting and recovery mechanisms

Cons of PEG.js

• Less flexible for dynamic grammar modifications at runtime
• Steeper learning curve for those unfamiliar with PEG syntax
• Limited support for incremental parsing

Code Comparison

PEG.js grammar example:

start
  = additive

additive
  = left:multiplicative "+" right:additive { return left + right; }
  / multiplicative

multiplicative
  = left:primary "*" right:multiplicative { return left * right; }
  / primary

primary
  = integer
  / "(" additive:additive ")" { return additive; }

integer "integer"
  = digits:[0-9]+ { return parseInt(digits.join(""), 10); }

Parsimmon equivalent:

const P = require('parsimmon');

const parser = P.createLanguage({
  start: r => r.additive,
  additive: r => P.alt(
    P.seq(r.multiplicative, P.string('+'), r.additive).map(([l, _, r]) => l + r),
    r.multiplicative
  ),
  multiplicative: r => P.alt(
    P.seq(r.primary, P.string('*'), r.multiplicative).map(([l, _, r]) => l * r),
    r.primary
  ),
  primary: r => P.alt(
    r.integer,
    P.seq(P.string('('), r.additive, P.string(')')).map(([_, a, __]) => a)
  ),
  integer: () => P.regexp(/[0-9]+/).map(Number)
});

Pros of Rouge

• Supports a wide range of programming languages for syntax highlighting
• Actively maintained with frequent updates and contributions
• Designed specifically for syntax highlighting, making it more specialized for this task

Cons of Rouge

• Limited to syntax highlighting, not a general-purpose parsing library
• May have a steeper learning curve for custom language support
• Ruby-specific, which might not be ideal for projects in other languages

Code Comparison

Parsimmon (JavaScript):

const P = require('parsimmon');
const parser = P.string('hello').then(P.string('world'));
const result = parser.parse('helloworld');

Rouge (Ruby):

require 'rouge'
lexer = Rouge::Lexers::HTML.new
formatter = Rouge::Formatters::HTML.new
highlighted = formatter.format(lexer.lex('<h1>Hello, world!</h1>'))

Summary

Parsimmon is a general-purpose parsing library for JavaScript, offering flexibility for various parsing tasks. Rouge, on the other hand, is a Ruby-based syntax highlighter with extensive language support. While Parsimmon allows for custom parser creation, Rouge excels in out-of-the-box syntax highlighting for numerous languages. The choice between them depends on the specific project requirements, programming language preference, and whether the focus is on general parsing or syntax highlighting.

Pros of Nearley

• Supports a wider range of grammar types, including context-sensitive grammars
• Generates fast, standalone JavaScript parsers
• Includes a built-in tokenizer (Moo) for lexical analysis

Cons of Nearley

• Steeper learning curve due to its unique grammar syntax
• Less flexibility in combining and manipulating parsers
• May produce larger output files for complex grammars

Code Comparison

Nearley grammar example:

main -> "hello" ws "world" {% d => ({ greeting: d[0], target: d[2] }) %}
ws -> [ \t\n\v\f]+

Parsimmon equivalent:

const parser = Parsimmon.seq(
  Parsimmon.string("hello"),
  Parsimmon.regexp(/[ \t\n\v\f]+/),
  Parsimmon.string("world")
).map(([greeting, _, target]) => ({ greeting, target }));

Both Nearley and Parsimmon are powerful parser libraries for JavaScript, but they cater to different use cases. Nearley excels in handling complex grammars and generating standalone parsers, while Parsimmon offers a more flexible, combinatorial approach that may be easier for developers familiar with functional programming concepts.

Pros of Ohm

• More powerful and flexible grammar definition syntax
• Built-in support for left-recursive rules
• Includes a visual debugger and editor for grammar development

Cons of Ohm

• Steeper learning curve due to its unique approach
• Less idiomatic JavaScript syntax compared to Parsimmon
• May be overkill for simpler parsing tasks

Code Comparison

Parsimmon example:

const P = require('parsimmon');
const parser = P.string('hello')
  .then(P.string(' '))
  .then(P.string('world'));

Ohm example:

const ohm = require('ohm-js');
const grammar = ohm.grammar(`
  Greeting {
    greeting = "hello" " " "world"
  }
`);

Both Parsimmon and Ohm are popular parsing libraries for JavaScript, but they have different approaches and strengths. Parsimmon uses a more functional, combinator-based style, while Ohm employs a grammar-based approach inspired by PEG parsers.

Parsimmon is generally easier to get started with for JavaScript developers, as its API closely resembles typical JavaScript patterns. It's well-suited for smaller parsing tasks and can be easily integrated into existing projects.

Ohm, on the other hand, offers more advanced features and is better suited for complex grammars. Its separate grammar definition syntax allows for more expressive and maintainable parser definitions, especially for larger projects. The visual tools provided by Ohm can be particularly helpful during development and debugging.

Pros of Chevrotain

• Higher performance due to its optimized parsing algorithm
• Better error reporting and recovery capabilities
• Supports a wider range of parsing techniques, including LL(k) and LR(1)

Cons of Chevrotain

• Steeper learning curve and more complex API
• Requires more boilerplate code for simple grammars
• Larger library size, which may impact bundle size in browser environments

Code Comparison

Parsimmon example:

const P = require('parsimmon');
const parser = P.string('hello').then(P.string('world'));
const result = parser.parse('helloworld');

Chevrotain example:

const { Lexer, CstParser } = require('chevrotain');
class MyParser extends CstParser {
  constructor() {
    super([/* token definitions */]);
    this.RULE('expression', () => {
      this.CONSUME('Hello');
      this.CONSUME('World');
    });
  }
}

Summary

Chevrotain offers more advanced features and better performance, making it suitable for complex parsing tasks. Parsimmon, on the other hand, provides a simpler API and is easier to get started with for basic parsing needs. The choice between the two depends on the complexity of the parsing requirements and the developer's familiarity with parsing concepts.