*At least for the people who send me mail about a new language that
they're designing, the general advice is: do it to learn about how
to write a compiler. Don't have any expectations that anyone will
use it, unless you hook up with some sort of organization in a
position to push it hard. It's a lottery, and some can buy a lot of
the tickets. There are plenty of beautiful languages (more beautiful
than C) that didn't catch on. But someone does win the lottery, and
doing a language at least teaches you something.*

`Dennis Ritchie`_ (1941-2011) Creator of the C_ programming
language and of Unix_

|TatSu|

|TatSu| is a tool that takes grammars in a variation of EBNF_ as input, and
outputs memoizing_ (Packrat) PEG parsers in Python_.

Why use a PEG_ parser? Because regular languages_ (those parsable with Python's re package) "cannot count". Any language with nested structures or with balancing of demarcations requires more than regular expressions to be parsed.

|TatSu| can compile a grammar stored in a string into a
tatsu.grammars.Grammar object that can be used to parse any given
input, much like the re_ module does with regular expressions, or it can generate a Python_ module that implements the parser.

|TatSu| supports left-recursive_ rules in PEG_ grammars using the
algorithm_ by Laurent and Mens. The generated AST_ has the expected left associativity.

|TatSu| requires a maintained version of Python (>=3.12 at the moment). While no code
in |TatSu| yet depends on new language or standard library features,
the authors don't want to be constrained by Python version compatibility considerations
when developing features that will be part of future releases.

If you need support for previous versions of Python, please consider TatSu-LTS_,
a friendly fork of |TatSu| aimed at compatibility with other versions of Python still used by
many projects. The developers of both projects work together to promote compatibility
with most versions of Python.

.. _algorithm: http://norswap.com/pubs/sle2016.pdf
.. _TatSu-LTS: https://pypi.org/project/TatSu-LTS/

Installation

.. code-block:: bash

$ pip install TatSu

Using the Tool

|TatSu| can be used as a library, much like Python's re, by embedding grammars as strings and generating grammar models instead of generating Python code.

This compiles the grammar and generates an in-memory parser that can subsequently be used for parsing input with:

.. code-block:: python

parser = tatsu.compile(grammar)

Compiles the grammar and parses the given input producing an AST_ as result:

.. code-block:: python

ast = tatsu.parse(grammar, input)

The result is equivalent to calling:

.. code-block:: python

parser = compile(grammar)
ast = parser.parse(input)

Compiled grammars are cached for efficiency.

This compiles the grammar to the Python_ sourcecode that implements the parser:

.. code-block:: python

parser_source = tatsu.to_python_sourcecode(grammar)

This is an example of how to use |TatSu| as a library:

.. code-block:: python

GRAMMAR = '''
    @@grammar::CALC


    start = expression $ ;


    expression
        =
        | expression '+' term
        | expression '-' term
        | term
        ;


    term
        =
        | term '*' factor
        | term '/' factor
        | factor
        ;


    factor
        =
        | '(' expression ')'
        | number
        ;


    number = /\d+/ ;
'''


if __name__ == '__main__':
    import json
    from tatsu import parse
    from tatsu.util import asjson

    ast = parse(GRAMMAR, '3 + 5 * ( 10 - 20 )')
    print(json.dumps(asjson(ast), indent=2))

..

|TatSu| will use the first rule defined in the grammar as the start rule.

This is the output:

.. code-block:: console

[
  "3",
  "+",
  [
    "5",
    "*",
    [
      "10",
      "-",
      "20"
    ]
  ]
]

Documentation

For a detailed explanation of what |TatSu| is capable of, please see the
documentation_.

.. _documentation: http://tatsu.readthedocs.io/

Questions?

Please use the [tatsu]_ tag on StackOverflow_ for general Q&A, and limit
Github issues to bugs, enhancement proposals, and feature requests.

.. _[tatsu]: https://stackoverflow.com/tags/tatsu/info

Changes

See the RELEASES_ for details.

License

You may use |TatSu| under the terms of the BSD-style license
described in the enclosed LICENSE.txt file. If your project
requires different licensing please email_.

.. |fury| image:: https://badge.fury.io/py/TatSu.svg
:target: https://badge.fury.io/py/TatSu
.. |license| image:: https://img.shields.io/badge/license-BSD-blue.svg
:target: https://raw.githubusercontent.com/neogeny/tatsu/master/LICENSE.txt
.. |pyversions| image:: https://img.shields.io/pypi/pyversions/tatsu.svg
:target: https://pypi.python.org/pypi/tatsu
.. |actions| image:: https://github.com/neogeny/TatSu/actions/workflows/default.yml/badge.svg
:target: https://github.com/neogeny/TatSu/actions/workflows/default.yml
.. |docs| image:: https://readthedocs.org/projects/tatsu/badge/?version=stable
:target: http://tatsu.readthedocs.io/en/stable/
.. |downloads| image:: https://img.shields.io/pypi/dm/TatSu.svg
:target: https://pypistats.org/packages/tatsu

Dependencies of TatSu (2).
Dependency	Optional
colorama	true
rich	true

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TatSu

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