lite-lexer

A light-weight PHP-based string lexer. By defining parser blocks, a simple syntax can be defined. The parser will then build a tree representing the parsed string. This can then be interpreted for other uses.

I created this for a simple query language to read custom data from a model system, but it can easily be adapted to other syntaxes. It has relatively low overhead, and based on my testing performed fast (enough so for my application).

Installation

This package is available via composer and can be added to a project using the command:

$ composer require nathanntg/lite-lexer

Usage

The recommended usage is to subclass LiteLexer\Parser to define your own syntax blocks (see the example implementation). Then you can run your parser as follows:

$parser = new MyParser();

// parse string
$tree = $parser->parseString($string_to_parse);

// optional: remove unneeded leaves and branches
$tree->prune();

// print debugging tree
$tree->debug();

Example Implementation

The example folder contains a QueryParser class that implements the parser needed to read a basic query language. Specifically, given an input string like the following:

customer.namelast='' AND customer.namefirst = '' OR ( customer.namelast='' AND customer.namefirst='' )  ORDER customer.namelast DESC , customer.namelast   LIMIT 2

It will produce the following parse tree:

root
	query
		conditions_main
			condition_set_values
				conditions
					condition
						condition_standard
							column; raw "customer.namelast"; customer.namelast
							operator
								unnamed leaf; raw "="; =
							value
								value_string; raw "''";
				condition_operator
					unnamed leaf; raw "AND"; AND
				conditions
					condition
						condition_standard
							column; raw "customer.namefirst"; customer.namefirst
							operator
								unnamed leaf; raw "="; =
							value
								value_string; raw "''";
				condition_operator
					unnamed leaf; raw "OR"; OR
				conditions
					condition_set
						unnamed leaf; raw "("; (
						condition_set_values
							conditions
								condition
									condition_standard
										column; raw "customer.namelast"; customer.namelast
										operator
											unnamed leaf; raw "="; =
										value
											value_string; raw "''";
							condition_operator
								unnamed leaf; raw "AND"; AND
							conditions
								condition
									condition_standard
										column; raw "customer.namefirst"; customer.namefirst
										operator
											unnamed leaf; raw "="; =
										value
											value_string; raw "''";
						unnamed leaf; raw ")"; )
		order_by_main
			unnamed leaf; raw "ORDER"; ORDER
			order_by_columns
				order_by_column
					column; raw "customer.namelast"; customer.namelast
					order_by_direction
						unnamed leaf; raw "DESC"; DESC
				order_by_column
					column; raw "customer.namelast"; customer.namelast
		limit_main
			unnamed leaf; raw "LIMIT"; LIMIT
			limit_count; raw "2"; 2

Testing

You can run the PHPUnit tests using the following command (assuming installed via composer, and includes the developer requirements):

$ vendor/bin/phpunit tests