Arpeggio is parser interpreter based on PEG grammars implemented as recursive descent parser with memoization (aka Pacrat parser).
Arpeggio is part of research project whose main goal is building environment for DSL development. The main domain of application is IDE for DSL development but it can be used for all sort of general purpose parsing. Some essential planed/done features are error reporting and error recovery as well as access to the raw parse tree in order to support syntax highlighting and other nice features of today's IDEs.
- For more information on PEG and pacrat parsers see:
Arpeggio is written in Python programming language and distributed with setuptools support. Install it with the following command
python setup.py install
after installation you should be able to import arpeggio python module with
import arpeggio
There is no documentation at the moment. See examples for some ideas of how it can be used.
Here is a basic explanation of how arpeggio works and the definition of some terms used in the arpeggio project.
Language grammar is specified using PEG's textual notation (similar to EBNF) or python language constructs (lists, tuples, functions...). This grammar representation, whether in textual or python form, is referred to as "the parser model". Parser is constructed out of the parser model. Parser is a tree of python objects where each object is an instance of class which represents parsing expressions from PEG (i.e. Sequence, OrderedChoice, ZeroOrMore). This tree is referred to as "the parser model tree".
This design choice requires some upfront work during initialization phase so arpeggio may not be well suited for one-shot parsing where parser needs to be initialized every time parsing is performed and the speed is of the utmost importance. Arpeggio is designed to be used in integrated development environments where parser is constructed once (usually during IDE start-up) and used many times.
Once constructed, parser can be used to transform input text to a tree representation where tree structure must adhere to the parser model. This tree representation is called "parse tree". After construction of parse tree it is possible to construct Astract Syntax Tree or, more generally, Abstract Semantic Graph(ASG) using semantic actions. ASG is constructed using two-pass bottom-up walking of the parse tree. ASG, generally has a graph structure, but it can be any specialization of it (a tree or just a single node - see calc.py for the example of ASG constructed as a single node/value). Python module arpeggio.peg is a good demonstration of how semantic action can be used to build PEG parser itself. See also peg_peg.py example where PEG parser is bootstraped using description given in PEG language itself.