README

A Simple PHP Roman Numerals Library

Usage

This library includes a simple couple of filters to convert a string with Roman number to an int that represents the input as decimal and decimal int to a string with Roman number as result.

use Romans\Filter\RomanToInt;

$filter = new RomanToInt();
$result = $filter->filter('MCMXCIX'); // 1999

use Romans\Filter\IntToRoman;

$filter = new IntToRoman();
$result = $filter->filter(1999); // MCMXCIX

Installation

This package uses Composer as default repository. You can install it adding the name of package in require section of composer.json, pointing to the last stable version.

{
  "require": {
    "wandersonwhcr/romans": "^1.0"
  }
}

Also, Romans uses Semantic Versioning. The following package versions support these PHP releases:

• Romans 1.0.*: PHP ^7.0 (Augustus)
• Romans 1.1.*: PHP ^7.0 (Tiberius)
• Romans 1.2.*: PHP >=7.4 (Caligula)
• Romans 1.3.*: PHP >=7.4 (Claudius)
• Romans 1.4.*: PHP >=7.4 (Nero)
• Romans 1.5.*: PHP >=8.0 (Galba)

Integrations

This library can be used as dependency for projects, making integrations with libraries or frameworks easier. If you want to add more items in this list, please, open an issue or create a pull request, adding your project alphabetically.

• Illuminate Romans: Laravel Illuminate Romans Integration
• Kirby Romans: Kirby CMS Integration
• Laminas Romans: Laminas Project Romans Integration
• Plates Romans Extension: Plates Extension
• Twig Roman Numerals Extension: Twig Extension (Symfony, WordPress + Timber)
• Zend Romans: Zend Framework Romans Integration DEPRECATED

Advanced Usage

The Romans package uses a Lexer-Parser approach and a Deterministic Finite Automaton (DFA) to convert Roman number to int, using a Grammar Token library.

use Romans\Grammar\Grammar;
use Romans\Lexer\Lexer;
use Romans\Parser\Parser;

$grammar = new Grammar();
$lexer   = new Lexer($grammar);
$parser  = new Parser($grammar);

$tokens = $lexer->tokenize('MCMXCIX');

/*
$tokens = [
    0 => 'M'  // Grammar::T_M
    1 => 'C', // Grammar::T_C
    2 => 'M', // Grammar::T_M
    3 => 'X', // Grammar::T_X
    4 => 'C', // Grammar::T_C
    5 => 'I', // Grammar::T_I
    6 => 'X', // Grammar::T_X
];
*/

$result = $parser->parse($tokens); // 1999

Exception Handling

The filter RomanToInt uses Lexer to tokenize the input and Parser to build the int number. When errors are found, the Lexer or Parser throw Exceptions to notify the problem with a specific code.

use Romans\Filter\RomanToInt;
use Romans\Lexer\Exception as LexerException;
use Romans\Parser\Exception as ParserException;

$filter = new RomanToInt();

try {
    $filter->filter($input);
} catch (LexerException $e) {
    // Unknown Token (LexerException::UNKNOWN_TOKEN)
} catch (ParserException $e) {
    // Invalid Token Type (Not String) (ParserException::INVALID_TOKEN_TYPE)
    // Unknown Token (ParserException::UNKNOWN_TOKEN)
    // Invalid Roman (ParserException::INVALID_ROMAN)
}

You can use this structure to validate Roman numbers, adding a try..catch block to check if $input is valid. Also, you can validate if an int can be filtered to Roman using an IntToRoman filter.

use Romans\Filter\IntToRoman;
use Romans\Filter\Exception as FilterException;

$filter = new IntToRoman();

try {
    $filter->filter($input);
} catch (FilterException $e) {
    // Invalid Integer (< 0) (FilterException::INVALID_INTEGER)
}

Zero

The zero value is represented as string "N", the initial of nulla or nihil, the Latin word for "nothing" (see references).

use Romans\Filter\RomanToInt;
use Romans\Filter\IntToRoman;

$filter = new RomanToInt();
$result = $filter->filter('N'); // 0 (Zero)

$filter = new IntToRoman();
$result = $filter->filter(0); // N

Cache

This package uses PSR-6 Caching Interface to improve execution, mainly over loops (like while or foreach) using cache libraries. Any PSR-6 implementation can be used and we suggest Symfony Cache package.

use Romans\Filter\IntToRoman;
use Romans\Filter\RomanToInt;
use Symfony\Component\Cache\Adapter\ArrayAdapter;

$cache = new ArrayAdapter();

$filter = new RomanToInt();
$filter->setCache($cache);
$result = $filter->filter('MCMXCIX'); // 1999
$result = $filter->filter('MCMXCIX'); // 1999 (from cache)

$filter = new IntToRoman();
$filter->setCache($cache);
$result = $filter->filter(1999); // MCMXCIX
$result = $filter->filter(1999); // MCMXCIX (from cache)

Development

You can use Docker Compose to build an image and run a container to develop and test this package.

docker-compose build
docker-compose run --rm romans composer install
docker-compose run --rm romans composer test

Techniques

This section describes techniques used by this package to convert Roman numbers into int and vice-versa.

Lexer-Parser

A Lexer-Parser approach was chosen because the validating and reading of Roman numbers are more simplified: the Lexer is responsible for reading and transform the input into tokens, validating content at char level; and the Parser is responsible for transform tokens into numbers, validating content at position level and converting to int through a DFA.

Wikipedia says that "lexical analysis is the process of converting a sequence of characters into a sequence of tokens", that "is a structure representing a lexeme that explicity indicates its categorization for the purpose of parsing". Even, Wikipedia says that "parsing or syntax analysis is the process of analysing symbols conforming to the rules of a formal grammar".

This structure makes easier the development of a structure responsible to read an input string, converting it to another structure according to specific charset and its position inside input.

Deterministic Finite Automaton (DFA)

A DFA was developed to check if a string with Roman number is valid. This technique was choiced because other implementations simply convert the input without checking rules, like four chars sequentially.

The current automaton definition is declared below.

M  = (Q, Σ, δ, q0, F)
Q  = { a, b, c, d, e, f, g, y, z }
Σ  = { I, V, X, L, C, D, M, N }
q0 = g
F  = { z }

z -> ε
y -> $z
a -> y | Iy  | IIy | IIIy
b -> a | IVy | Va  | IXy
c -> b | Xb  | XXb | XXXb
d -> c | XLb | Lc  | XCb
e -> d | Cd  | CCd | CCCd
f -> e | CDd | De  | CMd
g -> f | Ny  | Mg

References

• Rapid Tables: How to Convert Roman Numerals to Numbers
• Wikipedia: Zero in Roman Numerals
• Wikipedia: Lexical Analysis
• Wikipedia: Parsing
• Wikipedia: Deterministic Finite Automaton

License

This package is opensource and available under MIT license described in LICENSE.