Welcome

Welcome to the melody documentation!

Melody is a language that compiles to regular expressions and aims to be more easily readable and maintainable

Examples

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

Batman Theme

16 of "na";

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

// 🦇🦸‍♂️

Turns into

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

Twitter Hashtag

"#";
some of <word>;

// #melody

Turns into

#\w+

Introductory Courses

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

// classname 1xx

Turns into

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

Indented Code (2 spaces)

some of match {
  2 of <space>;
}

some of <char>;
";";

// let value = 5;

Turns into

(?: {2})+.+;

Semantic Versions

<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 by visiting the playground

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

Should be the following once the registry is updated.

If you've successfuly installed via this method please open an issue and let me know.

Thanks!
```
nix-env -i melody
```

CLI

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

Crates

melody_compiler - The Melody compiler crates.io docs.rs
melody_cli - A CLI wrapping the Melody compiler crates.io docs.rs

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. captured 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)

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

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

Extensions

Packages

NodeJS
Deno

Integrations

Babel Plugin

Changelog

[v0.20.0] - 2024-11-24

Breaking

Sets the MSRV to Rust 1.70.0

Fixes

Removes use of atty as it is unmaintained and has a low CVE

Dependencies

Updates dependencies

Refactoring

Clippy fixes

[v0.19.0] - 2023-07-16

Breaking

Sets the MSRV to Rust 1.65.0

Features

Adds console.error output for panics on the Wasm version
Deno no longer requires an init function

Fixes

Fixes a few edge cases with hyphens and slashes

Dependencies

Updates dependencies

Refactoring

Clippy fixes

[v0.18.1] - 2022-06-25

Fixes

Fixes playground link

Dependencies

Updates dependencies

Refactoring

Clippy fixes

[v0.18.0] - 2022-04-24

Features

Adds support for unicode categories

Misc.

Update dependencies

[v0.17.0] - 2022-04-23

Features

Add support for testing matches in a file in the CLI

Refactoring

Remove anyhow in compiler in favor of emitting specific error variants

[v0.16.0] - 2022-04-13

Features

Add support for testing matches in CLI

[v0.15.0] - 2022-04-13

Features

Add shell completions for CLI
Add Deno support

[v0.14.0] - 2022-04-11

Features

Support stdin in CLI
Emit proper exit codes on specific errors

[v0.13.10] - 2022-03-11

Fixes

Fixes unnecessary grouping in quantifiers

[v0.13.9] - 2022-03-11

Misc.

Version bump for documentation update

[v0.13.8] - 2022-03-11

Misc.

Version bump for documentation update

[v0.13.7] - 2022-03-11

Misc.

Version bump for documentation update

[v0.13.6] - 2022-03-11

Fixes

Handles a few possible panics

[v0.13.5] - 2022-03-11

Misc.

Version bump

[v0.13.4] - 2022-03-11

Tooling

Strips binaries

Dependencies

Updates dependencies

[v0.13.3] - 2022-03-09

Refactoring

Replaces lazy_static with once_cell

[v0.13.2] - 2022-03-09

Performance

Improves literal parse performance

Refactoring

Reports a few possible panics with a ParseError

[v0.13.1] - 2022-03-08

Fixes

Fixes an issue with single letter variable identifiers matching a following space
Fixes a clash between REPL commands and variables

[v0.13.0] - 2022-03-08

Breaking

<alphabet> is now <alphabetic>

Features

Support for lazy quantifiers
All symbols now have negative counterparts
<alphanumeric> symbol added
Adds an experimental implementation of variables

[v0.12.4] - 2022-03-06

Misc.

Version bump

[v0.12.3] - 2022-03-06

Fixes

Fixes an issue with identifying negative char ranges

[v0.12.2] - 2022-03-05

Refactoring

Performance improvements

Misc.

Adds keywords and categories to cargo.toml files

[v0.12.1] - 2022-03-04

Misc.

CLI documentation update

[v0.12.0] - 2022-03-04

Breaking

Produces clean output (no // and new newline after output)

Features

Adds favicons for documentation and playground
The Melody playground now supports add to homescreen
Adds #![forbid(unsafe_code)]

Benchmarks

Adds benchmarks

[v0.11.1] - 2022-03-03

Fixes

Fixes possible panics

Tests

Adds tests
Adds tests for CLI

Refactoring

Removes duplicated code

[v0.11.0] - 2022-03-02

Breaking

ParseError now contains only one message field, may be changed in the future
Line comments (//) may only be used in a separate line
The REPL currently accepts blocks on a single line but not multiple lines
Semicolons are no longer optional