pegged 0.3.3
Parsing Expression Grammar (PEG) generator
To use this package, run the following command in your project's root directory:
Manual usage
Put the following dependency into your project's dependences section:
PEGGED
Pegged is a parsing expression grammar (PEG) generator implemented in the D programming language.
The idea is to give the generator a PEG, with the syntax presented in the reference article . From this grammar definition a set of related parsers will be created, to be used at runtime or compile time.
Usage
To use Pegged, just call the grammar
function with a PEG and mix it in. For example:
import pegged.grammar;
mixin(grammar(`
Arithmetic:
Term < Factor (Add / Sub)*
Add < "+" Factor
Sub < "-" Factor
Factor < Primary (Mul / Div)*
Mul < "*" Primary
Div < "/" Primary
Primary < Parens / Neg / Pos / Number / Variable
Parens < "(" Term ")"
Neg < "-" Primary
Pos < "+" Primary
Number < ~([0-9]+)
Variable <- identifier
`));
This creates the Arithmetic
grammar, with the Expr
, Add
, Factor
(and so on) rules for basic arithmetic expressions with operator precedence ('*' and '/' bind stronger than '+' or '-'). identifier
is a pre-defined parser recognizing your basic C-style identifier (first a letter or underscore, then digits, letters or underscores). In the rest of this document, I'll call 'rule' a Parser <- Parsing Expression
expression and I'll use 'grammar' to designate the entire group of rules given to grammar
.
To use a grammar, call it with a string. It will return a parse tree containing the calls to the different rules:
// Parsing at compile-time:
enum parseTree1 = Arithmetic("1 + 2 - (3*x-5)*6");
pragma(msg, parseTree1.matches);
assert(parseTree1.matches == ["1", "+", "2", "-", "(", "3", "*", "x", "-", "5", ")", "*", "6"]);
writeln(parseTree1);
// And at runtime too:
auto parseTree2 = Arithmetic(" 0 + 123 - 456 ");
assert(parseTree2.matches == ["0", "+", "123", "-", "456"]);
Even for such a simple grammar and such a simple expression, the resulting parse tree is a bit long to be shown here. See the result here
By default, the grammars do not silently consume spaces, as this is the standard behaviour for PEGs. There is an opt-out though, with the simple <
arrow instead of <-
(you can see it in the previous example).
How to get Pegged
Pegged is a github project, hosted at https://github.com/PhilippeSigaud/Pegged
To get it:
$ git clone https://github.com/PhilippeSigaud/Pegged
The /docs
directory contains an empty /wiki
directory, linked to the github wiki as a git submodule.
Here is how to get it:
$ cd <pegged directory>
$ git submodule init
$ git submodule update
This should give you a /docs/wiki
directory full of markdown files, right from the online wiki.
Tutorial and docs
The Pegged wiki is here. It contains a growing tutorial. All the wiki pages are also present (as Markdown files) in the docs
directory.
Features
- The complete set of operators described here are implemented, with the 'traditional' PEG syntax. See Peg Basics.
- Pegged can parse its input at compile time and generate a complete parse tree at compile time. In a word: compile-time string (read: D code) transformation and generation. See Generating Code for example.
- You can parse at runtime also, you lucky you. (Using the Parse Tree)
- Use a standard and readable PEG syntax as a DSL, not a bunch of templates that hide the parser in noise.
- But you can use expression templates if you want, as parsers are all available as such. Pegged is implemented as an expression template, and what's good for the library writer is sure OK for the user too. (Behind the Curtain: How Pegged Works
- Some useful additional operators are there too: a way to discard matches (thus dumping them from the parse tree), to push captures on a stack, to accept matches that are equal to another match: see PEG Additions.
- Adding new parsers is easy. See User-Defined Parsers to see how to do that.
- Grammars are composable: you can put different
mixin(grammar(rules));
in a module and then grammars and rules can refer to one another. That way, you can have utility grammars providing their functionalities to other grammars. Grammar Composition - That's why Pegged comes with some pre-defined grammars (JSON, C, XML, CSV, D, the PEG grammar itself, etc). See Grammar Examples.
- Grammars can be dumped in a file to create a module. Use the
asModule(string moduleName, string gram)
function inpegged.grammar
to do that. See Grammars as Modules.
More advanced features, outside the standard PEG perimeter are there to bring more power in the mix:
- Parametrized rules:
"List(E, Sep) <- E (Sep E)*"
is possible. The previous rule defines a parametrized parser taking two other parsers (namely,E
andSep
) to match aSep
-separated list ofE
's. Entire grammars can be parametrized, too. See Parametrized Rules to see what's possible. - Semantic actions can be added to any rule in a grammar. Once a rule has matched, its associated action is called on the rule output and passed as final result to other parsers further up the grammar. Do what you want to the parse tree. If the passed actions are delegates, they can access external variables. See Semantic Actions.
References
Articles:
D Code:
- Hisayuki Mima's CTPG, very similar, also done in D. Have a look!
- Nick Sabalausky's Goldie.
- Benjamin Shropshire's dparser.
- Martin Nowak put these gists on the D newsgroup:
- https://gist.github.com/1255439 - lexer generator
- https://gist.github.com/1262321 - complete and fast D lexer
Other languages:
- pegtl, the PEG Template Library, in C++.
- chilon::parser in C++ also.
- metaparse, in C++, is able to parse at compile-time.
- Parslet in Ruby and Treetop, in Ruby also.
License
Pegged is released with the Boost license (like most D projects). See here for more details.
- Registered by Philippe Sigaud
- 0.3.3 released 8 years ago
- PhilippeSigaud/Pegged
- Boost
- Copyright © 2012-2016, Philippe Sigaud
- Authors:
- Dependencies:
- none
- Versions:
-
0.4.9 2023-Sep-01 0.4.8 2023-Mar-31 0.4.7 2023-Feb-28 0.4.6 2022-May-10 0.4.5 2021-Apr-30 - Download Stats:
-
-
7 downloads today
-
108 downloads this week
-
480 downloads this month
-
257461 downloads total
-
- Score:
- 4.7
- Short URL:
- pegged.dub.pm