Ingy döt Net > Pegex-0.20 > Pegex

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Module Version: 0.20   Source   Latest Release: Pegex-0.25

NAME ^

Pegex - Acmeist PEG Parsing Framework

SYNOPSIS ^

    use Pegex;
    my $data = pegex($grammar)->parse($input);

or with regular expression sugar:

    use Pegex::Regex;
    $input =~ qr{$grammar}x;
    my $data = \%/;

or with options:

    use Pegex;
    use ReceiverClass;
    my $parser = pegex($grammar, {receiver => 'ReceiverClass'});
    my $data = $parser->parse(input);

or more explicitly:

    use Pegex::Parser;
    use Pegex::Grammar;
    use Pegex::Compiler;
    my $pegex_grammar = Pegex::Grammar->new(
        tree => Pegex::Compiler->compile($grammar)->tree,
    );
    my $parser = Pegex::Parser->new(
        grammar => $pegex_grammar,
    );
    my $data = $parser->parse($input);

or customized explicitly:

    package MyGrammar;
    use Mo;
    extends 'Pegex::Grammar';

    has text => default => sub {
        "your grammar definition text goes here";
    };
    has receiver => default => sub{"MyReceiver"};

    package MyReceiver;
    use base 'Pegex::Receiver';
    got_some_rule { ... }
    got_other_rule { ... }

    package main;
    use Pegex::Parser;
    my $parser = Pegex::Parser->new(
        grammar => MyGrammar->new,
        receiver => MyReceiver->new,
    );
    $parser->parse($input);
    my $data = $parser->receiver->data;

DESCRIPTION ^

Pegex is a Acmeist parser framework. It allows you to easily create parsers that will work equivalently in lots of programming langugages!

Pegex gets it name by combining Parsing Expression Grammars (PEG), with Regular Expessions (regex). That's actually what Pegex does.

PEG is the cool new way to elegantly specify recursive descent grammars. The Perl 6 language is defined in terms of a self modifying PEG language called Perl 6 Rules. Regular expressions are familar to programmers of most modern programming languages. Pegex defines a simple PEG syntax, where all the terminals are regular expressions. This means that Pegex can be quite fast and powerful.

Pegex attempts to be the simplest way to define new (or old) Domain Specific Languages (DSLs) that need to be used in several programming languages and environments.

Pegex MODULE USAGE ^

The Pegex.pm module itself is just a trivial way to use the Pegex framework. It is only intended for the simplest of uses.

This module exports a single function, pegex, which takes a Pegex grammar string as input. You may also pass a second parameter which is a hash opject of options.

The pegex function returns a Pegex::Parser object, on which you would typically call the parse() method, which (on success) will return a data structure of the parsed data.

PEGEX OVERVIEW ^

In the diagram below, there is a simple language called Foo. The diagram shows how Pegex can take a text grammar defining Foo and generate a parser that can parse Foo sources into data (abstract syntax trees).

                            Parsing a language called "Foo"
                               with the Pegex toolset.

                              .-----------------------.
  .--------------------.      |    Pegex::Compiler    |
  |    Foo Language    |      |-----------------------|    Serialize
  |--------------------|----->| Pegex::Grammar::Pegex |---------.
  | Pegex grammar text |      | Pegex::Receiver       |         |
  '--------------------'      '-----------------------'         v
  ......................                  |                 .------.
  |                    |                  | compile()       | YAML |
  |foo:: <verb> <noun> |                  v                 '------'
  |verb: /Hello/       |       .--------------------.       .------.
  |noun: /world/       |       | Foo grammar tree   |       | JSON |
  |                    |       '--------------------'       '------'
  ......................                  |                 .------.
                                          |                 | Perl |
                                          v                 '------'
                               .---------------------.      .--------.
                               | Pegex::Grammar::Foo |      | Python |
                               |---------------------|      '--------'
                               | Pegex::Parser       |      .-----.
                               | Pegex::AST::Foo     |      | etc |
   .-----------------.         '---------------------'      '-----'
   |  Foo Language   |                    |
   |-----------------|------------------->| parse()
   | Foo source text |                    v
   '-----------------'        .----------------------.
   ...................        | Parsed Foo Data Tree |
   |Hello world      |        '----------------------'
   ...................        ........................
                              |- verb: Hello         |
                              |- noun: world         |
                              ........................

FYI ^

Pegex is self-hosting. This means that the Pegex grammar language syntax is defined by a Pegex grammar! This is important because (just like any Pegex based language) it makes it easier to port to new programming languages. You can find the Pegex grammar for Pegex grammars here: http://github.com/ingydotnet/pegex-pgx/.

Pegex was originally inspired by Perl 6 Rules. It also takes ideas from Damian Conway's Perl 5 module, Regexp::Grammars. Pegex tries to take the best ideas from these great works, and make them work in as many languages as possible. That's Acmeism.

SELF COMPILATION TRICKS ^

You can have some fun using Pegex to compile itself. First get the Pegex grammar repo:

    git clone git://github.com/ingydotnet/pegex-pgx.git
    cd pegex-pgx

Then parse and dump the Pegex grammar with Pegex:

    perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx")->parse("pegex.pgx")'

For a different view of the data tree, try:

    perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx", {wrap => 0})->parse("pegex.pgx")'

Finally to emulate the Pegex compiler do this:

    perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx", {receiver => "Pegex::Pegex::AST"})->parse("pegex.pgx")'

This specifies a "receiving" class that can shape the results into something useful. Indeed, this is the exact guts of Pegex::Grammar::Pegex.

A REAL WORLD EXAMPLE ^

TestML is a new Acmeist unit test language. It is perfect for software that needs to run equivalently in more than one language. In fact, Pegex itself is tested with TestML!!

TestML has a language specification grammar: http://www.testml.org/specification/language/

The Perl6 implementation of TestML uses this grammar in: https://github.com/ingydotnet/testml-pm6/blob/master/lib/TestML/Parser/Grammar.pm

All other implementations of TestML use this Pegex grammar: https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx

In Perl 5, Pegex::Compiler is used to compile the grammar into this simple data structure (shown in YAML): https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx.yaml

The grammar can also be precompiled to JSON: https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx.json

Pegex::Compiler further compiles this into a Perl 5 only grammar tree, which becomes this module: https://github.com/ingydotnet/testml-pm/blob/master/lib/TestML/Grammar.pm

TestML::Parser::Grammar is a subclass of Pegex::Grammar. It can be used to parse TestML files. TestML::Parser calls the parse() method of the grammar with a TestML::AST object that receives callbacks when various rules match, and uses the information to build a TestML::Document object.

Thus TestML is an Acmeist language written in Pegex. It can be easily ported to every language where Pegex exists. In fact, it must be ported to those languages in order to test the new Pegex implementation!

SEE ALSO ^

AUTHOR ^

Ingy döt Net <ingy@cpan.org>

COPYRIGHT AND LICENSE ^

Copyright (c) 2010, 2011, 2012. Ingy döt Net.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

See http://www.perl.com/perl/misc/Artistic.html

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