Melody is a language that compiles to ECMAScript regular expressions, while aiming to be more readable and maintainable.

Examples

Note: these are for the currently supported syntax and may change

Batman Theme  _{^{try in playground}}

16 of "na";

2 of match {
  <space>;
  "batman";
}

// 🦇🦸‍♂️

Turns into

(?:na){16}(?: batman){2}

Twitter Hashtag  _{^{try in playground}}

"#";
some of <word>;

// #melody

Turns into

#\w+

Introductory Courses  _{^{try in playground}}

some of <alphabetic>;
<space>;
"1";
2 of <digit>;

// classname 1xx

Turns into

[a-zA-Z]+ 1\d{2}

Indented Code (2 spaces)  _{^{try in playground}}

some of match {
  2 of <space>;
}

some of <char>;
";";

// let value = 5;

Turns into

(?: {2})+.+;

Semantic Versions  _{^{try in playground}}

<start>;

option of "v";

capture major {
  some of <digit>;
}

".";

capture minor {
  some of <digit>;
}

".";

capture patch {
  some of <digit>;
}

<end>;

// v1.0.0

Turns into

^v?(?<major>\d+)\.(?<minor>\d+)\.(?<patch>\d+)$

Playground

You can try Melody in your browser using the playground

Book

Read the book here

Install

Cargo

cargo install melody_cli

From Source

git clone https://github.com/yoav-lavi/melody.git
cd melody
cargo install --path crates/melody_cli

Binary

• macOS binaries (aarch64 and x86_64) can be downloaded from the release page

Community

• Brew (macOS and Linux)

  Installation instructions

  brew install melody

• Arch Linux (maintained by @ilai-deutel)

  Installation instructions

  1. Installation with an AUR helper, for instance using paru:

     paru -Syu melody

  2. Install manually with makepkg:

     git clone https://aur.archlinux.org/melody.git
     cd melody
     makepkg -si

• NixOS (maintained by @jyooru)

  Installation instructions

  1. Declarative installation using /etc/nixos/configuration.nix:

     { pkgs, ... }:
     {
       environment.systemPackages = with pkgs; [
         melody
       ];
     }

  2. Imperative installation using nix-env:

     nix-env -iA nixos.melody

CLI Usage

USAGE:
    melody [OPTIONS] [INPUT_FILE_PATH]

ARGS:
    <INPUT_FILE_PATH>    Read from a file
                         Use '-' and or pipe input to read from stdin

OPTIONS:
    -f, --test-file <TEST_FILE>
            Test the compiled regex against the contents of a file

        --generate-completions <COMPLETIONS>
            Outputs completions for the selected shell
            To use, write the output to the appropriate location for your shell

    -h, --help
            Print help information

    -n, --no-color
            Print output with no color

    -o, --output <OUTPUT_FILE_PATH>
            Write to a file

    -r, --repl
            Start the Melody REPL

    -t, --test <TEST>
            Test the compiled regex against a string

    -V, --version
            Print version information

Changelog

See the changelog here or in the release page

Syntax

Quantifiers

• ... of - used to express a specific amount of a pattern. equivalent to regex {5} (assuming 5 of ...)
• ... to ... of - used to express an amount within a range of a pattern. equivalent to regex {5,9} (assuming 5 to 9 of ...)
• over ... of - used to express more than an amount of a pattern. equivalent to regex {6,} (assuming over 5 of ...)
• some of - used to express 1 or more of a pattern. equivalent to regex +
• any of - used to express 0 or more of a pattern. equivalent to regex *
• option of - used to express 0 or 1 of a pattern. equivalent to regex ?

All quantifiers can be preceded by lazy to match the least amount of characters rather than the most characters (greedy). Equivalent to regex +?, *?, etc.

Symbols

• <char> - matches any single character. equivalent to regex .
• <space> - matches a space character. equivalent to regex
• <whitespace> - matches any kind of whitespace character. equivalent to regex \s or [ \t\n\v\f\r]
• <newline> - matches a newline character. equivalent to regex \n
• <tab> - matches a tab character. equivalent to regex \t
• <return> - matches a carriage return character. equivalent to regex \r
• <feed> - matches a form feed character. equivalent to regex \f
• <null> - matches a null characther. equivalent to regex \0
• <digit> - matches any single digit. equivalent to regex \d or [0-9]
• <vertical> - matches a vertical tab character. equivalent to regex \v
• <word> - matches a word character (any latin letter, any digit or an underscore). equivalent to regex \w or [a-zA-Z0-9_]
• <alphabetic> - matches any single latin letter. equivalent to regex [a-zA-Z]
• <alphanumeric> - matches any single latin letter or any single digit. equivalent to regex [a-zA-Z0-9]
• <boundary> - Matches a character between a character matched by <word> and a character not matched by <word> without consuming the character. equivalent to regex \b
• <backspace> - matches a backspace control character. equivalent to regex [\b]

All symbols can be preceeded with not to match any character other than the symbol

Special Symbols

• <start> - matches the start of the string. equivalent to regex ^
• <end> - matches the end of the string. equivalent to regex $

Unicode Categories

Note: these are not supported when testing in the CLI (-t or -f) as the regex engine used does not support unicode categories. These require using the u flag.

• <category::letter> - any kind of letter from any language
  • <category::lowercase_letter> - a lowercase letter that has an uppercase variant
  • <category::uppercase_letter> - an uppercase letter that has a lowercase variant.
  • <category::titlecase_letter> - a letter that appears at the start of a word when only the first letter of the word is capitalized
  • <category::cased_letter> - a letter that exists in lowercase and uppercase variants
  • <category::modifier_letter> - a special character that is used like a letter
  • <category::other_letter> - a letter or ideograph that does not have lowercase and uppercase variants
• <category::mark> - a character intended to be combined with another character (e.g. accents, umlauts, enclosing boxes, etc.)
  • <category::non_spacing_mark> - a character intended to be combined with another character without taking up extra space (e.g. accents, umlauts, etc.)
  • <category::spacing_combining_mark> - a character intended to be combined with another character that takes up extra space (vowel signs in many Eastern languages)
  • <category::enclosing_mark> - a character that encloses the character it is combined with (circle, square, keycap, etc.)
• <category::separator> - any kind of whitespace or invisible separator
  • <category::space_separator> - a whitespace character that is invisible, but does take up space
  • <category::line_separator> - line separator character U+2028
  • <category::paragraph_separator> - paragraph separator character U+2029
• <category::symbol> - math symbols, currency signs, dingbats, box-drawing characters, etc
  • <category::math_symbol> - any mathematical symbol
  • <category::currency_symbol> - any currency sign
  • <category::modifier_symbol> - a combining character (mark) as a full character on its own
  • <category::other_symbol> - various symbols that are not math symbols, currency signs, or combining characters
• <category::number> - any kind of numeric character in any script
  • <category::decimal_digit_number> - a digit zero through nine in any script except ideographic scripts
  • <category::letter_number> - a number that looks like a letter, such as a Roman numeral
  • <category::other_number> - a superscript or subscript digit, or a number that is not a digit 0–9 (excluding numbers from ideographic scripts)
• <category::punctuation> - any kind of punctuation character
  • <category::dash_punctuation> - any kind of hyphen or dash
  • <category::open_punctuation> - any kind of opening bracket
  • <category::close_punctuation> - any kind of closing bracket
  • <category::initial_punctuation> - any kind of opening quote
  • <category::final_punctuation> - any kind of closing quote
  • <category::connector_punctuation> - a punctuation character such as an underscore that connects words
  • <category::other_punctuation> - any kind of punctuation character that is not a dash, bracket, quote or connectors
• <category::other> - invisible control characters and unused code points
  • <category::control> - an ASCII or Latin-1 control character: 0x00–0x1F and 0x7F–0x9F
  • <category::format> - invisible formatting indicator
  • <category::private_use> - any code point reserved for private use
  • <category::surrogate> - one half of a surrogate pair in UTF-16 encoding
  • <category::unassigned> - any code point to which no character has been assigned

These descriptions are from regular-expressions.info

Character Ranges

• ... to ... - used with digits or alphabetic characters to express a character range. equivalent to regex [5-9] (assuming 5 to 9) or [a-z] (assuming a to z)

Literals

• "..." or '...' - used to mark a literal part of the match. Melody will automatically escape characters as needed. Quotes (of the same kind surrounding the literal) should be escaped

Raw

• `...` - added directly to the output without any escaping

Groups

• capture - used to open a capture or named capture block. capture patterns are later available in the list of matches (either positional or named). equivalent to regex (...)
• match - used to open a match block, matches the contents without capturing. equivalent to regex (?:...)
• either - used to open an either block, matches one of the statements within the block. equivalent to regex (?:...|...)

Assertions

• ahead - used to open an ahead block. equivalent to regex (?=...). use after an expression
• behind - used to open an behind block. equivalent to regex (?<=...). use before an expression

Assertions can be preceeded by not to create a negative assertion (equivalent to regex (?!...), (?<!...))

Variables

• let .variable_name = { ... } - defines a variable from a block of statements. can later be used with .variable_name. Variables must be declared before being used. Variable invocations cannot be quantified directly, use a group if you want to quantify a variable invocation

  example:

  let .a_and_b = {
    "a";
    "b";
  }
  
  .a_and_b;
  "c";
  
  // abc

Extras

• /* ... */, // ... - used to mark comments (note: // ... comments must be on separate line)

File Extension

The Melody file extensions are .mdy and .melody

Crates

• melody_compiler - The Melody compiler 📦 📖
• melody_cli - A CLI wrapping the Melody compiler 📦 📖
• melody_wasm - WASM bindings for the Melody compiler

Extensions

• VSCode
• IntelliJ

Packages

• NodeJS
• Deno

Integrations

• Babel Plugin

Performance

Last measured on v0.20.0

Measured on an 8 core 2021 MacBook Pro 14-inch, Apple M1 Pro using criterion:

• 8 lines:

  compiler/normal (8 lines)
                            time:   [4.3556 µs 4.3674 µs 4.3751 µs]
  slope  [4.3556 µs 4.3751 µs] R^2            [0.9996144 0.9996931]
  mean   [4.3377 µs 4.3678 µs] std. dev.      [16.019 ns 30.154 ns]
  median [4.3270 µs 4.3777 µs] med. abs. dev. [3.1402 ns 41.334 ns]
  

• 1M lines:

  compiler/long input (1M lines)
                            time:   [470.04 ms 472.35 ms 474.78 ms]
  mean   [470.04 ms 474.78 ms] std. dev.      [2.0458 ms 5.3453 ms]
  median [469.54 ms 475.24 ms] med. abs. dev. [734.10 µs 6.8144 ms]
  

• Deeply nested:

  compiler/deeply nested
                            time:   [4.2357 µs 4.2561 µs 4.2782 µs]
  slope  [4.2357 µs 4.2782 µs] R^2            [0.9988854 0.9988087]
  mean   [4.2474 µs 4.2752 µs] std. dev.      [13.698 ns 29.574 ns]
  median [4.2426 µs 4.2819 µs] med. abs. dev. [2.7127 ns 43.193 ns]
  

To reproduce, run cargo bench or cargo xtask benchmark

Future Feature Status

🐣 - Partially implemented

❌ - Not implemented

❔ - Unclear what the syntax will be

❓ - Unclear whether this will be implemented

Melody	Regex	Status
not "A";	[^A]	🐣
variables / macros		🐣
<...::...>	\p{...}	🐣
not <...::...>	\P{...}	🐣
file watcher		❌
multiline groups in REPL		❌
flags: global, multiline, ...	/.../gm...	❔
(?)	\#	❔
(?)	\k<name>	❔
(?)	\uYYYY	❔
(?)	\xYY	❔
(?)	\ddd	❔
(?)	\cY	❔
(?)	$1	❔
(?)	$`	❔
(?)	$&	❔
(?)	x20	❔
(?)	x{06fa}	❔
any of "a", "b", "c" *	[abc]	❓
multiple ranges *	[a-zA-Z0-9]	❓
regex optimization		❓
standard library / patterns		❓
reverse compiler		❓

* these are expressable in the current syntax using other methods