Comparison with other projects

This wiki has a list of projects with similar goals to Pomsky. Here’s a list of the most popular projects:

Project	Types	GitHub
Melody	Transpiled
Pomsky	Transpiled
Egg Expressions	Transpiled App: Oil shell
Rx Expressions	Transpiled App: Emacs
Raku Grammars	App: Raku
Rosie	App: Rosie
SRL	DSL: PHP
Super Expressive	DSL: JS
Verbal Expressions	DSL: JS
Swift RegexBuilder	DSL: Swift

Since this content is likely to get out of date, I encourage you to update it.

Types #

Transpiled #

These languages are transpiled to “normal” regular expressions and can therefore be used anywhere. They usually have command-line interface to compile expressions.

Application specific #

Some regex languages are specific to a certain application or programming language. For example, Raku grammars can only be used in Raku; egg expressions are transpiled, but they are only available in the Oil shell.

DSLs #

DSLs (domain-specific languages) are languages that are embedded in another language using the host language’s syntax. For example, Verbal Expressions uses JavaScript methods:

const tester = VerEx()
  .startOfLine()
  .then('http')
  .maybe('s')
  .then('://')
  .maybe('www.')
  .anythingBut(' ')
  .endOfLine()

This page currently only discusses transpiled languages, but I welcome contributions.

Compatibility #

Let’s see what Regex flavors are supported by transpiled languages.

^*Melody can only emit ECMAScript regexes, but they also happen to be compatible with several other flavors.

Explanation of the flavors #

• ERE (extended regular expressions) are used by tools such as GNU grep and awk. Because ERE supports only the most basic features, it is mostly forward compatible with other regex flavors.

• ECMAScript is the syntax used in JavaScript and related languages (TypeScript, Elm, Dart, etc.) that are compiled to JS.

• PCRE (an acronym for “Perl compatible regular expression”) is the syntax used by the PCRE2 regex engine, which is the default in at least Crystal, Delphi, Elixir, Erlang, Hack, Julia, PHP, R and Vala. It’s also a popular choice in other languages like C and C++ and is used in many applications such as the Apache server, nginx, MariaDB, MongoDB, and optionally in GNU grep.

• .NET refers to the Regex class in .NET languages such as C# and F#.

• Java refers to the Pattern class in Java’s standard library. Equivalent to Kotlin’s and Scala’s regular expressions.

• Ruby refers to built-in regular expressions in Ruby.

• Python refers to Pythons re module. Note that Python 3 is required for good Unicode support.

• Rust refers to Rust’s popular regex crate (used by ripgrep)

Many more flavors exist, which are not (or only partially) supported by Pomsky and other languages.

Features #

Let’s see what Regex features are supported by languages that are transpiled to regular expressions.

Basic regex features #

^*Character ranges and negated sets in Melody only support ASCII letters, digits and a few special characters.

Advanced features #

Note that Melody and Pomsky support inline regexes. Because of this, all Regex features are technically supported in Melody and Pomsky, but using inline regexes may be less ergonomic and more dangerous to use than properly supported features.

^*All languages can match a code point with the dot, if multiline mode is enabled in the regex engine.

^**Pomsky can currently optimize repetitions, remove redundant or empty groups and deduplicate code points in character sets. More optimizations are planned.

Tooling #

Language integrations #

Packages #

IDE features #

¹ indentation based
² works in playground VSCode, but not in the playground
³ does not take scopes into account

Found a mistake? Please fix it on GitHub.