1Pegex::Miscellany(3) User Contributed Perl Documentation Pegex::Miscellany(3)
2
6 This document contains things about Pegex that were written but seemed
7 out of place in their original documents. Still they are possibly
8 useful so live here for now.
9
11 In the diagram below, there is a simple language called Foo. The
12 diagram shows how Pegex can take a text grammar defining Foo and
13 generate a parser that can parse Foo sources into data (abstract syntax
14 trees).
15 Parsing a language called "Foo"
17 with the Pegex toolset.
18 .-----------------------.
20 .--------------------. | Pegex::Compiler |
21 | Foo Language | |-----------------------| Serialize
22 |--------------------|----->| Pegex::Grammar::Pegex |---------.
23 | Pegex grammar text | | Pegex::Receiver | |
24 '--------------------' '-----------------------' v
25 ...................... | .------.
26 | | | compile() | YAML |
27 |foo: verb noun | v '------'
28 |verb: /Hello/ | .--------------------. .------.
29 |noun: /world/ | | Foo grammar tree | | JSON |
30 | | '--------------------' '------'
31 ...................... | .------.
32 | | Perl |
33 v '------'
34 .---------------------. .--------.
35 | Pegex::Grammar::Foo | | Python |
36 |---------------------| '--------'
37 | Pegex::Parser | .-----.
38 | Pegex::AST::Foo | | etc |
39 .-----------------. '---------------------' '-----'
40 | Foo Language | |
41 |-----------------|------------------->| parse()
42 | Foo source text | v
43 '-----------------' .----------------------.
44 ................... | Parsed Foo Data Tree |
45 |Hello world | '----------------------'
46 ................... ........................
47 |- verb: Hello |
48 |- noun: world |
49 ........................
50
52 Pegex is self-hosting. This means that the Pegex grammar language
53 syntax is defined by a Pegex grammar! This is important because (just
54 like any Pegex based language) it makes it easier to port to new
55 programming languages. You can find the Pegex grammar for Pegex
56 grammars here: <http://github.com/ingydotnet/pegex-pgx/>.
57 Pegex was originally inspired by Perl 6 Rules. It also takes ideas from
59 Damian Conway's Perl 5 module, Regexp::Grammars. Pegex tries to take
60 the best ideas from these great works, and make them work in as many
61 languages as possible. That's Acmeism.
62
64 You can have some fun using Pegex to compile itself. First get the
65 Pegex grammar repo:
66 git clone git://github.com/ingydotnet/pegex-pgx.git
68 cd pegex-pgx
69 Then parse and dump the Pegex grammar with Pegex:
71 perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx")->parse("pegex.pgx")'
73 For a different view of the data tree, try:
75 perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx", receiver => "Pegex::Tree")->parse("pegex.pgx")'
77 Finally to emulate the Pegex compiler do this:
79 perl -MXXX -MPegex -e 'XXX pegex("pegex.pgx", receiver => "Pegex::Pegex::AST")->parse("pegex.pgx")'
81 This specifies a "receiving" class that can shape the results into
83 something useful. Indeed, this is the exact guts of
84 Pegex::Grammar::Pegex.
85
87 TestML is a new Acmeist unit test language. It is perfect for software
88 that needs to run equivalently in more than one language. In fact,
89 Pegex itself is tested with TestML!!
90 TestML has a language specification grammar:
92 <http://www.testml.org/specification/language/>
93 The Perl6 implementation of TestML uses this grammar in:
95 <https://github.com/ingydotnet/testml-pm6/blob/master/lib/TestML/Parser/Grammar.pm>
96 All other implementations of TestML use this Pegex grammar:
98 <https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx>
99 In Perl 5, Pegex::Compiler is used to compile the grammar into this
101 simple data structure (shown in YAML):
102 <https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx.yaml>
103 The grammar can also be precompiled to JSON:
105 <https://github.com/ingydotnet/testml-pgx/blob/master/testml.pgx.json>
106 Pegex::Compiler further compiles this into a Perl 5 only grammar tree,
108 which becomes this module:
109 <https://github.com/ingydotnet/testml-pm/blob/master/lib/TestML/Compiler/Pegex/Grammar.pm>
110 TestML::Parser::Grammar is a subclass of Pegex::Grammar. It can be used
112 to parse TestML files. TestML::Parser calls the parse() method of the
113 grammar with a TestML::AST object that receives callbacks when various
114 rules match, and uses the information to build a TestML::Document
115 object.
116 Thus TestML is an Acmeist language written in Pegex. It can be easily
118 ported to every language where Pegex exists. In fact, it must be ported
119 to those languages in order to test the new Pegex implementation!
120perl v5.30.1 2020-02-17 Pegex::Miscellany(3)