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[Parsing & Serialization](/categories/parsing) 4. / 5. nielssp/parco ActiveLibrary[Parsing & Serialization](/categories/parsing) nielssp/parco ============= PHP parser combinators library. v1.1.1(10y ago)032MITPHPPHP >=5.4.0 Since Nov 15Pushed 10y ago1 watchersCompare [ Source](https://github.com/nielssp/parco)[ Packagist](https://packagist.org/packages/nielssp/parco)[ Docs](http://parco.nielssp.dk)[ RSS](/packages/nielssp-parco/feed)WikiDiscussions master Synced 2mo ago READMEChangelog (3)Dependencies (2)Versions (4)Used By (0) Parco – PHP parser combinators ============================== [](#parco--php-parser-combinators) [![Build Status](https://camo.githubusercontent.com/3a0792393582f3932d570fb048df00c3170481dd31ee03630b32ca58db07e887/68747470733a2f2f7472617669732d63692e6f72672f6e69656c7373702f706172636f2e7376673f6272616e63683d6d6173746572)](https://travis-ci.org/nielssp/parco) [![Coverage Status](https://camo.githubusercontent.com/64338c805ea18ad0e2f1dc72c9b71bafa8f57d2d965fc8d8280e15dbd8505bd7/68747470733a2f2f636f766572616c6c732e696f2f7265706f732f6e69656c7373702f706172636f2f62616467652e7376673f6272616e63683d6d617374657226736572766963653d676974687562)](https://coveralls.io/github/nielssp/parco?branch=master) [![Latest Stable Version](https://camo.githubusercontent.com/3279ad2feaafb4417e0c0346bcca48db57d04468e67c0c287705e9bfd3a1657d/68747470733a2f2f706f7365722e707567782e6f72672f6e69656c7373702f706172636f2f762f737461626c65)](https://packagist.org/packages/nielssp/parco) Parco is an experimental parser combinator library for PHP inspired by [Scala Parser Combinators](https://github.com/scala/scala-parser-combinators). See also [Wikipedia](https://en.wikipedia.org/wiki/Parser_combinator) for general information on parser combinators. The API documentation is available on [parco.nielssp.dk/api](http://parco.nielssp.dk/api). Install ------- [](#install) Requirements: - PHP 5.4 or newer Install using composer: ``` composer require nielssp/parco ``` Usage ----- [](#usage) See the `examples` directory for some examples: - `calculator.php` is a simple calculator made using `RegexParsers` based on [this example in the Scala Parser Combinators documentation](http://www.scala-lang.org/files/archive/api/2.11.2/scala-parser-combinators/#scala.util.parsing.combinator.RegexParsers). - `json.php` is a JSON parser using `RegexParsers`. - `lexer.php` is a lexer/scanner for a small expression language based on the λ-calculus. - `tokens.php` is a parser using `PositionalParsers` to convert the token sequence produced by `lexer.php` into an abstract syntax tree. ### Writing a parser [](#writing-a-parser) To write a parser using Parco simply use one of the combinator traits in a class. There are currently three traits: - [Parsers](http://parco.nielssp.dk/api/class-Parco.Combinator.Parsers.html) for generic parser combinators (the user must provide an input sequence implementation), - [RegexParsers](http://parco.nielssp.dk/api/class-Parco.Combinator.RegexParsers.html) (extends `Parsers`) for parsing strings, and - [PositionalParsers](http://parco.nielssp.dk/api/class-Parco.Combinator.PositionalParsers.html) (extends `Parsers`) for parsing arrays of objects that implement the `Positional` interface (e.g. a list of tokens from a lexer). ``` class Myparser { use \Parco\Combinator\RegexParsers; } ``` To implement a parser you may define multiple subparsers and combine them using combinators. Each subparser is implemented as a parameterless method returning a `Parser` object. It usually makes sense to have a method for each production rule in your language grammar, so for a grammar such as: ``` expr ::= term {"+" term | "-" term} term ::= factor {"*" factor | "/" factor} factor ::= "(" expr ")" | number number ::= digit {digit} ["." digit {digit}] ``` our parser class may have the following structure: ``` class Myparser { use \Parco\Combinator\RegexParsers; public function expr() { return // a parser for expressions } public function term() { return // a parser for terms } public function factor() { return // a parser for factors } public function number() { return // a parser for numbers } } ``` You may also want to add a method for invoking the parser: ``` class MyParser { use \Parco\Combinator\RegexParsers; // ... public function __invoke($string) { return $this->parseAll($this->expr, $string)->get(); } } ``` The `parseAll` method is provided by the `RegexParsers` trait. It converts the input string to a sequence of characters and makes sure that there is no leftover input after the given parser has been applied. Now we can use the parser by constructing and then invoking it: ``` $myParser = new MyParser(); echo $myParser('1 + 5 - 7 / 2'); ``` If the parser fails, a `ParseException` is thrown. The "Error handling" section below explains how to handle parse errors. ### Terminals [](#terminals) The follwing parsers can be used to parse one or more input sequence elements: ``` $this->elem('a') // exact element $this->acceptIf(function ($elem) { return $elem instanceof NumberToken; }) // predicate $this->char('a') // character (RegexParsers) $this->string('goto') // string (RegexParsers) ``` Additionally `RegexParsers` provides a method for parsing input sequence elements using regular expressions, e.g.: ``` $this->regex('/[a-z][a-z0-9]*/i') ``` The above parsers serve as the basic building blocks for constructing more advanced parsers. The following section shows how to combine them. ### From grammar to code [](#from-grammar-to-code) Some basic combinators provided by `Parsers`: - Sequencing: `a b c` (`a` followed by `b` followed by `c`): ``` $this->seq($this->a, $this->b, $this->c) ``` If you want to parse `a` followed by `b`, but only want to keep the result of `a`, the method `seqL` can be used: ``` $this->a->seqL($this->b) ``` Similarily, `seqR` can be used to keep the result of `b` instead. - Alternation: `a | b | c` (`a`, `b`, or `c`): ``` $this->alt($this->a, $this->b, $this->c) ``` - Repetition: `{a}` (zero or more repetitions of `a`): ``` $this->rep($this->a) ``` - Option: `[a]` (zero or one `a`): ``` $this->opt($this->a) ``` More combinators are described on the [API documentation page](http://parco.nielssp.dk/api/class-Parco.Combinator.Parsers.html). ### Manipulating parser results [](#manipulating-parser-results) The abstract `Parser` class provides some methods for manipulating the result of a parser. The most important one is the `map`-method, which converts the result of a parser using a function, e.g.: ``` $this->regex('/\d+/')->map(function ($digits) { return intval($digits); }); ``` The above parser uses a regular expression to parse one or more digits, then converts the result to and integer. Two other useful methods are: - `withResult` replace the result of a parser: ``` $this->string('true')->withResult(true); ``` - `withFailure` set a custom failure message: ``` $this->regex('/\d+/')->withFailure('expected an integer'); ``` ### Recursion [](#recursion) The `Parsers` trait provides a magic getter that converts parameterless parsers into lazy parsers. This can be used to implement recursive grammars such as the follwing: ``` expr ::= term "-" term term ::= "(" expr ")" | number ``` To use this feature simply refererence your parser functions without parentheses (e.g. `$this->expr` instead of `$this->expr()`): ``` public function expr() { return $this->seq($this->term, $this->char("-"), $this->term); } public function term() { return $this->alt( $this->seq($this->char("("), $this->expr, $this->char(")")), $this->number ); } ``` ### Left recursion [](#left-recursion) Some left-recursive grammars (e.g. left-associative operators) such as ``` expr ::= expr "-" term | term ``` can be implemented using the `chainl`-combinator: ``` public function expr() { return $this->chainl( $this->term, $this->char('-')->withResult(function ($left, $right) { return $left - $right; }) ); } ``` The second parameter to `chainl` is a parser that parses the separator (i.e. the `'-'` terminal) and returns a function that combines parse result from left to right. Thus the result of parsing `8 - 4 - 1 - 3` with the above parser is `((8 - 4) - 1) - 3 = 0`. A similar combinator, `chainr`, can be used for right-associative operators. ### Error handling [](#error-handling) The result of a parser includes information about the line number and column number. This can be used to produce helpful error messages. An example of a parser error handler: ``` $result = $myParser($input); if (! $result->successful) { $lines = explode("\n", $input); $line = $result->getInputLine($lines); $column = $result->getInputColumn($lines); echo 'Syntax Error: ' . $result->message . ' on line ' . $line . ' column ' . $column . PHP_EOL; if ($line > 0) { echo $lines[$line - 1] . PHP_EOL; echo str_repeat('-', $column - 1) . '^'; } } ``` Which produces output such as: ``` Syntax Error: expected "->" on line 1 column 17 let x = 5 in \y - x + y ----------------^ ``` Parco also has an exception class, `ParseException`, that can be used to wrap parse errors. It is thrown automatically when calling `get()` on an unsuccessful parser result. License ------- [](#license) Copyright (C) 2015 Niels Sonnich Poulsen () Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. ### Health Score 26 — LowBetter than 43% of packages Maintenance20 Infrequent updates — may be unmaintained Popularity7 Limited adoption so far Community7 Small or concentrated contributor base Maturity60 Established project with proven stability Bus Factor1 Top contributor holds 100% of commits — single point of failure How is this calculated?**Maintenance (25%)** — Last commit recency, latest release date, and issue-to-star ratio. Uses a 2-year decay window. **Popularity (30%)** — Total and monthly downloads, GitHub stars, and forks. Logarithmic scaling prevents top-heavy scores. **Community (15%)** — Contributors, dependents, forks, watchers, and maintainers. Measures real ecosystem engagement. **Maturity (30%)** — Project age, version count, PHP version support, and release stability. ### Release Activity Cadence Every ~45 days Total 3 Last Release 3740d ago ### Community Maintainers ![](https://www.gravatar.com/avatar/51685bf382df70cc27e922167e7cd1911a447527cfae8a38c519426d201e396b?d=identicon)[nielssp](/maintainers/nielssp) --- Top Contributors [![nielssp](https://avatars.githubusercontent.com/u/424372?v=4)](https://github.com/nielssp "nielssp (52 commits)") --- Tags grammarlexerparserparser-combinatorsphpregular-expressionparsing ### Code Quality TestsPHPUnit Code StylePHP\_CodeSniffer ### Embed Badge ![Health badge](/badges/nielssp-parco/health.svg) ``` [![Health](https://phpackages.com/badges/nielssp-parco/health.svg)](https://phpackages.com/packages/nielssp-parco) ``` ### Alternatives [jakubledl/dissect Lexing and parsing in pure PHP 2244.6M11](/packages/jakubledl-dissect)[parsica-php/parsica The easiest way to build robust parsers in PHP. 412140.4k4](/packages/parsica-php-parsica)[jejik/mt940 An MT940 bank statement parser for PHP 911.2M2](/packages/jejik-mt940)[kingsquare/php-mt940 Simple MT940 parser in PHP 105806.1k2](/packages/kingsquare-php-mt940)[denissimon/formula-parser Parsing and evaluating mathematical formulas given as strings. 81306.8k3](/packages/denissimon-formula-parser)[codelicious/php-coda-parser PHP parser for Belgian CODA banking files 44352.9k1](/packages/codelicious-php-coda-parser) PHPackages © 2026 [Directory](/)[Categories](/categories)[Trending](/trending)[Changelog](/changelog)[Analyze](/analyze)