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

Documentation

Read the documentation 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

• 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 (soon, see PR) (maintained by @jyooru)

CLI Usage

melody [OPTIONS] [INPUT_FILE_PATH]

ARGS:
    <INPUT_FILE_PATH>    Read from a file

OPTIONS:
    -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
    -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 .
• <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 or [0-9]
• <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 $

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 extension is .mdy

Crates

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

Extensions

• VSCode

Performance

Last measured on V0.13.3

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

• 8 lines:

  compiler/normal (8 lines)
                          time:   [3.6560 us 3.6596 us 3.6644 us]
  slope  [3.6560 us 3.6644 us] R^2            [0.9999367 0.9999233]
  mean   [3.6577 us 3.6676 us] std. dev.      [3.2234 ns 11.399 ns]
  median [3.6549 us 3.6674 us] med. abs. dev. [642.70 ps 12.973 ns]
  

• 1M lines:

  compiler/long input (1M lines)
                          time:   [345.99 ms 348.85 ms 351.91 ms]
  mean   [345.99 ms 351.91 ms] std. dev.      [2.8317 ms 6.3397 ms]
  median [344.55 ms 352.85 ms] med. abs. dev. [893.36 us 8.5853 ms]
  

• Deeply nested:

  compiler/deeply nested
                          time:   [4.8259 us 4.8330 us 4.8399 us]
  slope  [4.8259 us 4.8399 us] R^2            [0.9998793 0.9998830]
  mean   [4.8259 us 4.8476 us] std. dev.      [7.6412 ns 24.306 ns]
  median [4.8234 us 4.8484 us] med. abs. dev. [4.1349 ns 30.340 ns]
  

To reproduce, run cargo 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		🐣
file watcher		❌
TS / JS build step		❌
multiline groups in REPL		❌
flags: global, multiline, ...	/.../gm...	❔
(?)	\#	❔
(?)	\k<name>	❔
(?)	\p{...}	❔
(?)	\P{...}	❔
(?)	\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