竜 TatSu generates Python parsers from grammars in a variation of EBNF
See the code.. Copyright © 2017-2026 Juancarlo Añez (apalala@gmail.com)
.. SPDX-License-Identifier: BSD-4-Clause
.. |dragon| unicode:: 0x7ADC .. unicode dragon
.. |nbsp| unicode:: 0xA0 .. non breakable space
.. |TatSu| replace:: |dragon|\ |nbsp|\ **TatSu**
.. |TatSu-LTS| replace:: |dragon|\ |nbsp|\ **TatSu-LTS**
.. _RELEASES: https://github.com/neogeny/TatSu/releases
| |license| |pyversions|
| |fury| |actions| |docs| |installs|
| |sponsor|
|
|TatSu|
=======
*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| is a tool that takes grammars in extended `EBNF`_ as input, and
outputs `memoizing`_ (`Packrat`_) `PEG`_ parsers in `Python`_. The classic
variations of EBNF_ (Tomassetti, EasyExtend, Wirth) and `ISO EBNF`_ are
supported as input grammar formats.
**Sibling Projects!**
Take a look at the sibling projects:
* `修TieXiu`_ in `Rust`
* `⻰OGoPEGo`_ in `Go`
* `꘩TS’emekwes`_ in `TypeScript`
They are functionally complete and pass all the |TatSu| test suite.
Some features are implemented differently to abide to the semantics and
idioms of each language (features being deprecated in |TatSu| are missing).
Prepare to be surprised at the performance differences, after thorough
optimization, of `Python` versus `Go`, `Rust`, and `TypeScript`.
.. _修TieXiu: https://pypi.org/project/TieXiu/
.. _`⻰OGoPEGo`: https://pypi.org/project/ogopego/
.. _`꘩TS’emekwes`: https://github.com/neogeny/tsemekwes
The New CLI Tool
----------------
.. image:: https://vhs.charm.sh/vhs-23V9mzFKttlDbN1znR0lY6.gif
:alt: New CLI tool demo
:width: 800px
Why use a `PEG`_ parser generator?
----------------------------------
Regular expressions are *“memory-less”*—they excel at finding flat patterns
like email addresses or phone numbers, but they fail once data becomes
hierarchical. Regular expressions cannot *"count"* or balance demarcations
(a regex cannot reliably validate whether opening and closing parenthesis are
matched in a nested math equation).
Parsing is the essential step up when you need to understand the **logic and
structure** of information rather than just its appearance. Parsing constructs
an **Abstract Syntax Tree** (AST_) of the input, a hierarchical map that
represents how different parts of a sequence relate to one another.
* **Recursive Structures:** Whenever a piece of data can contain
a version of itself (like a folder inside a folder, or a conditional
``if`` statement inside another ``if``), you need a parser to track the
depth and scope.
* **Translating Formats:** When converting one format into another, a
parser ensures that the *meaning* of the original structure is
preserved, preventing the *"data soup"* that occurs when using simple
find-and-replace tools.
* **Ambiguity Resolution:** In complex sequences, the same sub-sequence might
mean different things depending on where it sits in the tree. A parser
uses the surrounding context to decide how to treat that sequence,
whereas a regex treats every match in isolation.
* **Domain-Specific Languages (DSL):** Parsing allows the creation of
specialized *"mini-languages"* tailored to a specific field, such as hardware
description, music notation, or complex business rules.
* **Executable Logic:** While a regex can tell you if a string
*looks* like a command, a parser turns that string into an object that a
computer can actually execute, ensuring the order of operations and
dependencies are strictly followed.
|TatSu| can compile a grammar stored in a string into a ``Grammar`` object that
can be used to parse any given input (much like the `re`_ module does with regular
expressions). |TatSu| can also 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.
Compatibility
-------------
|TatSu| expects a maintained_ version of Python (>=3.13), but currently all tests
run in versions of Python down to Python 3.12. |TatSu| is also compatible with the
current pre-release version of Python 3.15.
*For older versions of Python, you may consider* `TatSu-LTS`_, *a
friendly fork of* |TatSu| *aimed at compatibility*.
.. _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`_ source code 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 = '''
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(ast.asjsons())
..
|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`_ file. *If your project
requires different licensing* please `email`_.
For Fun
-------
This is a diagram of the grammar for |TatSu|'s own grammar language:
.. code:: console
start ●─grammar─■
grammar[Grammar] ●─ [title](`TATSU`)──┬→───────────────────────────────────┬── [`rules`]+(rule)──┬→───────────────────────────────┬──⇥$
├→──┬─ [`directives`]+(directive)─┬──┤ ├→──┬─ [`rules`]+(rule)───────┬──┤
│ └─ [`keywords`]+(keyword)─────┘ │ │ └─ [`keywords`]+(keyword)─┘ │
└───────────────────────────────────<┘ └───────────────────────────────<┘
directive ●─'@@'─ !['keyword'] ✂ ───┬─ [name](──┬─'comments'─────┬─) ✂ ─'::' ✂ ─ [value](regex)────────────┬─ ✂ ──■
│ └─'eol_comments'─┘ │
├─ [name]('whitespace') ✂ ─'::' ✂ ─ [value](──┬─regex───┬─)────────────┤
│ ├─string──┤ │
│ ├─'None'──┤ │
│ ├─'False'─┤ │
│ └─`None`──┘ │
├─ [name](──┬─'nameguard'──────┬─) ✂ ───┬─'::' ✂ ─ [value](boolean)─┬──┤
│ ├─'ignorecase'─────┤ └─ [value](`True`)──────────┘ │
│ ├─'left_recursion'─┤ │
│ ├─'parseinfo'──────┤ │
│ └─'memoization'────┘ │
├─ [name]('grammar') ✂ ─'::' ✂ ─ [value](word)─────────────────────────┤
└─ [name]('namechars') ✂ ─'::' ✂ ─ [value](string)─────────────────────┘
keywords ●───┬─keywords─┬───■
└─────────<┘
keyword ●─'@@keyword' ✂ ─'::' ✂ ───┬→──────────────────────────────────┬───■
├→ @+(──┬─word───┬─)─ ![──┬─':'─┬─]─┤
│ └─string─┘ └─'='─┘ │
└──────────────────────────────────<┘
the_params_at_last ●───┬─ [kwparams](kwparams)─────────────────────────┬──■
├─ [params](params)',' ✂ ─ [kwparams](kwparams)─┤
└─ [params](params)─────────────────────────────┘
paramdef ●───┬─'[' ✂ ─ >(the_params_at_last) ']'─┬──■
├─'(' ✂ ─ >(the_params_at_last) ')'─┤
└─'::' ✂ ─ [params](params)─────────┘
rule[Rule] ●─ [decorators](──┬→──────────┬──) [name](name) ✂ ───┬─→ >(paramdef) ─┬───┬─→'<' ✂ ─ [base](known_name)─┬───┬─'='──┬─ ✂ ─ [exp](expre)ENDRULE ✂ ──■
├→decorator─┤ └─→──────────────┘ └─→───────────────────────────┘ ├─':='─┤
└──────────<┘ └─':'──┘
ENDRULE ●───┬── &[UNINDENTED]──────┬──■
├─EMPTYLINE──┬─→';'─┬──┤
│ └─→────┘ │
├─⇥$ │
└─';'──────────────────┘
UNINDENTED ●─/(?=\s*(?:\r?\n|\r)[^\s])/──■
EMPTYLINE ●─/(?:\s*(?:\r?\n|\r)){2,}/──■
decorator ●─'@'─ !['@'] ✂ ─ @(──┬─'override'─┬─)─■
├─'name'─────┤
└─'nomemo'───┘
params ●─ @+(first_param)──┬→────────────────────────────┬───■
├→',' @+(literal)─ !['='] ✂ ──┤
└────────────────────────────<┘
first_param ●───┬─path────┬──■
└─literal─┘
kwparams ●───┬→────────────┬───■
├→',' ✂ ─pair─┤
└────────────<┘
pair ●─ @+(word)'=' ✂ ─ @+(literal)─■
expre ●───┬─choice───┬──■
└─sequence─┘
choice[Choice] ●───┬─→'|' ✂ ──┬─ @+(option)──┬─'|' ✂ ─ @+(option)─┬───■
└─→────────┘ └───────────────────<┘
option[Option] ●─ @(sequence)─■
sequence[Sequence] ●───┬── &[element',']──┬→───────────────┬───┬──■
│ ├→',' ✂ ─element─┤ │
│ └───────────────<┘ │
└───┬── ![ENDRULE]element─┬─────────────┘
└────────────────────<┘
element ●───┬─rule_include─┬──■
├─named────────┤
├─override─────┤
└─term─────────┘
rule_include[RuleInclude] ●─'>' ✂ ─ @(known_name)─■
named ●───┬─named_list───┬──■
└─named_single─┘
named_list[NamedList] ●─ [name](name)'+:' ✂ ─ [exp](term)─■
named_single[Named] ●─ [name](name)':' ✂ ─ [exp](term)─■
override ●───┬─override_list──────────────┬──■
├─override_single────────────┤
└─override_single_deprecated─┘
override_list[OverrideList] ●─'@+:' ✂ ─ @(term)─■
override_single[Override] ●─'@:' ✂ ─ @(term)─■
override_single_deprecated[Override] ●─'@' ✂ ─ @(term)─■
term ●───┬─void───────────────┬──■
├─gather─────────────┤
├─join───────────────┤
├─left_join──────────┤
├─right_join─────────┤
├─empty_closure──────┤
├─positive_closure───┤
├─closure────────────┤
├─optional───────────┤
├─skip_to────────────┤
├─lookahead──────────┤
├─negative_lookahead─┤
├─cut────────────────┤
├─cut_deprecated─────┤
└─atom───────────────┘
group[Group] ●─'(' ✂ ─ @(expre)')' ✂ ──■
gather ●── &[atom'.{'] ✂ ───┬─positive_gather─┬──■
└─normal_gather───┘
positive_gather[PositiveGather] ●─ [sep](atom)'.{' [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
normal_gather[Gather] ●─ [sep](atom)'.{' ✂ ─ [exp](expre)'}'──┬─→'*' ✂ ──┬─ ✂ ──■
└─→────────┘
join ●── &[atom'%{'] ✂ ───┬─positive_join─┬──■
└─normal_join───┘
positive_join[PositiveJoin] ●─ [sep](atom)'%{' [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
normal_join[Join] ●─ [sep](atom)'%{' ✂ ─ [exp](expre)'}'──┬─→'*' ✂ ──┬─ ✂ ──■
└─→────────┘
left_join[LeftJoin] ●─ [sep](atom)'<{' ✂ ─ [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
right_join[RightJoin] ●─ [sep](atom)'>{' ✂ ─ [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
positive_closure[PositiveClosure] ●───┬─'{' @(expre)'}'──┬─'-'─┬─ ✂ ──┬──■
│ └─'+'─┘ │
└─ @(atom)'+' ✂ ────────────────┘
closure[Closure] ●───┬─'{' @(expre)'}'──┬─→'*'─┬─ ✂ ──┬──■
│ └─→────┘ │
└─ @(atom)'*' ✂ ─────────────────┘
empty_closure[EmptyClosure] ●─'{}' ✂ ─ @( ∅ )─■
optional[Optional] ●───┬─'[' ✂ ─ @(expre)']' ✂ ──────────┬──■
└─ @(atom)─ ![──┬─'?"'─┬─]'?' ✂ ──┘
├─"?'"─┤
└─'?/'─┘
lookahead[Lookahead] ●─'&' ✂ ─ @(term)─■
negative_lookahead[NegativeLookahead] ●─'!' ✂ ─ @(term)─■
skip_to[SkipTo] ●─'->' ✂ ─ @(term)─■
atom ●───┬─group────┬──■
├─token────┤
├─alert────┤
├─constant─┤
├─call─────┤
├─pattern──┤
├─dot──────┤
└─eof──────┘
call[Call] ●─word─■
void[Void] ●─'()' ✂ ──■
fail[Fail] ●─'!()' ✂ ──■
cut[Cut] ●─'~' ✂ ──■
cut_deprecated[Cut] ●─'>>' ✂ ──■
known_name ●─name ✂ ──■
name ●─word─■
constant[Constant] ●── &['`']──┬─/(?ms)```((?:.|\n)*?)```/──┬──■
├─'`' @(literal)'`'──────────┤
└─/`(.*?)`/──────────────────┘
alert[Alert] ●─ [level](/\^+/─) [message](constant)─■
token[Token] ●───┬─string─────┬──■
└─raw_string─┘
literal ●───┬─string─────┬──■
├─raw_string─┤
├─boolean────┤
├─word───────┤
├─hex────────┤
├─float──────┤
├─int────────┤
└─null───────┘
string ●─STRING─■
raw_string ●─//─ @(STRING)─■
STRING ●───┬─ @(/"((?:[^"\n]|\\"|\\\\)*?)"/─) ✂ ─────┬──■
└─ @(/r"'((?:[^'\n]|\\'|\\\\)*?)'"/─) ✂ ──┘
hex ●─/0[xX](?:\d|[a-fA-F])+/──■
float ●─/[-+]?(?:\d+\.\d*|\d*\.\d+)(?:[Ee][-+]?\d+)?/──■
int ●─/[-+]?\d+/──■
path ●─/(?!\d)\w+(?:::(?!\d)\w+)+/──■
word ●─/(?!\d)\w+/──■
dot[Dot] ●─'/./'─■
pattern[Pattern] ●─regexes─■
regexes ●───┬→─────────────┬───■
├→'+' ✂ ─regex─┤
└─────────────<┘
regex ●───┬─'/' ✂ ─ @(/(?:[^/\\]|\\/|\\.)*/─)'/' ✂ ──┬──■
├─'?' @(STRING)────────────────────────────┤
└─deprecated_regex─────────────────────────┘
deprecated_regex ●─'?/' ✂ ─ @(/(?:.|\n)*?(?=/\?)/─)//\?+/─ ✂ ──■
boolean ●───┬─'True'──┬──■
└─'False'─┘
null ●─'None'─■
eof[EOF] ●─'$' ✂ ──■
.. _ANTLR: http://www.antlr.org/
.. _AST: http://en.wikipedia.org/wiki/Abstract_syntax_tree
.. _Abstract Syntax Tree: http://en.wikipedia.org/wiki/Abstract_syntax_tree
.. _Algol W: http://en.wikipedia.org/wiki/Algol_W
.. _Algorithms + Data Structures = Programs: http://www.amazon.com/Algorithms-Structures-Prentice-Hall-Automatic-Computation/dp/0130224189/
.. _BSD: http://en.wikipedia.org/wiki/BSD_licenses#2-clause_license_.28.22Simplified_BSD_License.22_or_.22FreeBSD_License.22.29
.. _Basel Shishani: https://bitbucket.org/basel-shishani
.. _C: http://en.wikipedia.org/wiki/C_language
.. _CHANGELOG: https://github.com/neogeny/TatSu/releases
.. _CSAIL at MIT: http://www.csail.mit.edu/
.. _Cyclomatic complexity: http://en.wikipedia.org/wiki/Cyclomatic_complexity
.. _David Röthlisberger: https://bitbucket.org/drothlis/
.. _Dennis Ritchie: http://en.wikipedia.org/wiki/Dennis_Ritchie
.. _EBNF: http://en.wikipedia.org/wiki/Ebnf
.. _ISO EBNF: http://en.wikipedia.org/wiki/Ebnf
.. _English: http://en.wikipedia.org/wiki/English_grammar
.. _Euler: http://en.wikipedia.org/wiki/Euler_programming_language
.. _Grako: https://bitbucket.org/neogeny/grako/
.. _Jack: http://en.wikipedia.org/wiki/Javacc
.. _Japanese: http://en.wikipedia.org/wiki/Japanese_grammar
.. _KLOC: http://en.wikipedia.org/wiki/KLOC
.. _Kathryn Long: https://bitbucket.org/starkat
.. _Keywords: https://en.wikipedia.org/wiki/Reserved_word
.. _`left-recursive`: https://en.wikipedia.org/wiki/Left_recursion
.. _LL(1): http://en.wikipedia.org/wiki/LL(1)
.. _Marcus Brinkmann: http://blog.marcus-brinkmann.de/
.. _MediaWiki: http://www.mediawiki.org/wiki/MediaWiki
.. _Modula-2: http://en.wikipedia.org/wiki/Modula-2
.. _Modula: http://en.wikipedia.org/wiki/Modula
.. _Oberon-2: http://en.wikipedia.org/wiki/Oberon-2
.. _Oberon: http://en.wikipedia.org/wiki/Oberon_(programming_language)
.. _PEG and Packrat parsing mailing list: https://lists.csail.mit.edu/mailman/listinfo/peg
.. _PEG.js: http://pegjs.majda.cz/
.. _PEG: http://en.wikipedia.org/wiki/Parsing_expression_grammar
.. _PL/0: http://en.wikipedia.org/wiki/PL/0
.. _Packrat: http://bford.info/packrat/
.. _Pascal: http://en.wikipedia.org/wiki/Pascal_programming_language
.. _Paul Sargent: https://bitbucket.org/PaulS/
.. _Perl: http://www.perl.org/
.. _PyPy team: http://pypy.org/people.html
.. _PyPy: http://pypy.org/
.. _Python Weekly: http://www.pythonweekly.com/
.. _Python: http://python.org
.. _Reserved Words: https://en.wikipedia.org/wiki/Reserved_word
.. _Robert Speer: https://bitbucket.org/r_speer
.. _Ruby: http://www.ruby-lang.org/
.. _Semantic Graph: http://en.wikipedia.org/wiki/Abstract_semantic_graph
.. _StackOverflow: http://stackoverflow.com/tags/tatsu/info
.. _Sublime Text: https://www.sublimetext.com
.. _TatSu Forum: https://groups.google.com/forum/?fromgroups#!forum/tatsu
.. _UCAB: http://www.ucab.edu.ve/
.. _USB: http://www.usb.ve/
.. _Unix: http://en.wikipedia.org/wiki/Unix
.. _VIM: http://www.vim.org/
.. _WTK: http://en.wikipedia.org/wiki/Well-known_text
.. _Warth et al: http://www.vpri.org/pdf/tr2007002_packrat.pdf
.. _Well-known text: http://en.wikipedia.org/wiki/Well-known_text
.. _Wirth: http://en.wikipedia.org/wiki/Niklaus_Wirth
.. _`LICENSE`: LICENSE
.. _basel-shishani: https://bitbucket.org/basel-shishani
.. _blog post: http://dietbuddha.blogspot.com/2012/12/52python-encapsulating-exceptions-with.html
.. _context managers: http://docs.python.org/2/library/contextlib.html
.. _declensions: http://en.wikipedia.org/wiki/Declension
.. _drothlis: https://bitbucket.org/drothlis
.. _email: mailto:apalala@gmail.com
.. _exceptions: http://www.jeffknupp.com/blog/2013/02/06/write-cleaner-python-use-exceptions/
.. _franz\_g: https://bitbucket.org/franz_g
.. _gapag: https://bitbucket.org/gapag
.. _gegenschall: https://bitbucket.org/gegenschall
.. _gkimbar: https://bitbucket.org/gkimbar
.. _introduced: http://dl.acm.org/citation.cfm?id=964001.964011
.. _jimon: https://bitbucket.org/jimon
.. _keyword: https://en.wikipedia.org/wiki/Reserved_word
.. _keywords: https://en.wikipedia.org/wiki/Reserved_word
.. _lambdafu: http://blog.marcus-brinkmann.de/
.. _leewz: https://bitbucket.org/leewz
.. _linkdd: https://bitbucket.org/linkdd
.. _make a donation: https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=P9PV7ZACB669J
.. _maintained: https://devguide.python.org/versions/#supported-versions
.. _memoizing: http://en.wikipedia.org/wiki/Memoization
.. _nehz: https://bitbucket.org/nehz
.. _neumond: https://bitbucket.org/neumond
.. _parsewkt: https://github.com/cleder/parsewkt
.. _pauls: https://bitbucket.org/pauls
.. _pgebhard: https://bitbucket.org/pgebhard
.. _r\_speer: https://bitbucket.org/r_speer
.. _raw string literal: https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals
.. _re: https://docs.python.org/3.7/library/re.html
.. _regular languages: https://en.wikipedia.org/wiki/Regular_language
.. _regex: https://pypi.python.org/pypi/regex
.. _siemer: https://bitbucket.org/siemer
.. _sjbrownBitbucket: https://bitbucket.org/sjbrownBitbucket
.. _smc.mw: https://github.com/lambdafu/smc.mw
.. _starkat: https://bitbucket.org/starkat
.. _tonico\_strasser: https://bitbucket.org/tonico_strasser
.. _vinay.sajip: https://bitbucket.org/vinay.sajip
.. _vmuriart: https://bitbucket.org/vmuriart
.. |fury| image:: https://badge.fury.io/py/TatSu.svg
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竜 TatSu generates Python parsers from grammars in a variation of EBNF
See the code.. Copyright © 2017-2026 Juancarlo Añez (apalala@gmail.com)
.. SPDX-License-Identifier: BSD-4-Clause
.. |dragon| unicode:: 0x7ADC .. unicode dragon
.. |nbsp| unicode:: 0xA0 .. non breakable space
.. |TatSu| replace:: |dragon|\ |nbsp|\ **TatSu**
.. |TatSu-LTS| replace:: |dragon|\ |nbsp|\ **TatSu-LTS**
.. _RELEASES: https://github.com/neogeny/TatSu/releases
| |license| |pyversions|
| |fury| |actions| |docs| |installs|
| |sponsor|
|
|TatSu|
=======
*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| is a tool that takes grammars in extended `EBNF`_ as input, and
outputs `memoizing`_ (`Packrat`_) `PEG`_ parsers in `Python`_. The classic
variations of EBNF_ (Tomassetti, EasyExtend, Wirth) and `ISO EBNF`_ are
supported as input grammar formats.
**Sibling Projects!**
Take a look at the sibling projects:
* `修TieXiu`_ in `Rust`
* `⻰OGoPEGo`_ in `Go`
* `꘩TS’emekwes`_ in `TypeScript`
They are functionally complete and pass all the |TatSu| test suite.
Some features are implemented differently to abide to the semantics and
idioms of each language (features being deprecated in |TatSu| are missing).
Prepare to be surprised at the performance differences, after thorough
optimization, of `Python` versus `Go`, `Rust`, and `TypeScript`.
.. _修TieXiu: https://pypi.org/project/TieXiu/
.. _`⻰OGoPEGo`: https://pypi.org/project/ogopego/
.. _`꘩TS’emekwes`: https://github.com/neogeny/tsemekwes
The New CLI Tool
----------------
.. image:: https://vhs.charm.sh/vhs-23V9mzFKttlDbN1znR0lY6.gif
:alt: New CLI tool demo
:width: 800px
Why use a `PEG`_ parser generator?
----------------------------------
Regular expressions are *“memory-less”*—they excel at finding flat patterns
like email addresses or phone numbers, but they fail once data becomes
hierarchical. Regular expressions cannot *"count"* or balance demarcations
(a regex cannot reliably validate whether opening and closing parenthesis are
matched in a nested math equation).
Parsing is the essential step up when you need to understand the **logic and
structure** of information rather than just its appearance. Parsing constructs
an **Abstract Syntax Tree** (AST_) of the input, a hierarchical map that
represents how different parts of a sequence relate to one another.
* **Recursive Structures:** Whenever a piece of data can contain
a version of itself (like a folder inside a folder, or a conditional
``if`` statement inside another ``if``), you need a parser to track the
depth and scope.
* **Translating Formats:** When converting one format into another, a
parser ensures that the *meaning* of the original structure is
preserved, preventing the *"data soup"* that occurs when using simple
find-and-replace tools.
* **Ambiguity Resolution:** In complex sequences, the same sub-sequence might
mean different things depending on where it sits in the tree. A parser
uses the surrounding context to decide how to treat that sequence,
whereas a regex treats every match in isolation.
* **Domain-Specific Languages (DSL):** Parsing allows the creation of
specialized *"mini-languages"* tailored to a specific field, such as hardware
description, music notation, or complex business rules.
* **Executable Logic:** While a regex can tell you if a string
*looks* like a command, a parser turns that string into an object that a
computer can actually execute, ensuring the order of operations and
dependencies are strictly followed.
|TatSu| can compile a grammar stored in a string into a ``Grammar`` object that
can be used to parse any given input (much like the `re`_ module does with regular
expressions). |TatSu| can also 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.
Compatibility
-------------
|TatSu| expects a maintained_ version of Python (>=3.13), but currently all tests
run in versions of Python down to Python 3.12. |TatSu| is also compatible with the
current pre-release version of Python 3.15.
*For older versions of Python, you may consider* `TatSu-LTS`_, *a
friendly fork of* |TatSu| *aimed at compatibility*.
.. _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`_ source code 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 = '''
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(ast.asjsons())
..
|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`_ file. *If your project
requires different licensing* please `email`_.
For Fun
-------
This is a diagram of the grammar for |TatSu|'s own grammar language:
.. code:: console
start ●─grammar─■
grammar[Grammar] ●─ [title](`TATSU`)──┬→───────────────────────────────────┬── [`rules`]+(rule)──┬→───────────────────────────────┬──⇥$
├→──┬─ [`directives`]+(directive)─┬──┤ ├→──┬─ [`rules`]+(rule)───────┬──┤
│ └─ [`keywords`]+(keyword)─────┘ │ │ └─ [`keywords`]+(keyword)─┘ │
└───────────────────────────────────<┘ └───────────────────────────────<┘
directive ●─'@@'─ !['keyword'] ✂ ───┬─ [name](──┬─'comments'─────┬─) ✂ ─'::' ✂ ─ [value](regex)────────────┬─ ✂ ──■
│ └─'eol_comments'─┘ │
├─ [name]('whitespace') ✂ ─'::' ✂ ─ [value](──┬─regex───┬─)────────────┤
│ ├─string──┤ │
│ ├─'None'──┤ │
│ ├─'False'─┤ │
│ └─`None`──┘ │
├─ [name](──┬─'nameguard'──────┬─) ✂ ───┬─'::' ✂ ─ [value](boolean)─┬──┤
│ ├─'ignorecase'─────┤ └─ [value](`True`)──────────┘ │
│ ├─'left_recursion'─┤ │
│ ├─'parseinfo'──────┤ │
│ └─'memoization'────┘ │
├─ [name]('grammar') ✂ ─'::' ✂ ─ [value](word)─────────────────────────┤
└─ [name]('namechars') ✂ ─'::' ✂ ─ [value](string)─────────────────────┘
keywords ●───┬─keywords─┬───■
└─────────<┘
keyword ●─'@@keyword' ✂ ─'::' ✂ ───┬→──────────────────────────────────┬───■
├→ @+(──┬─word───┬─)─ ![──┬─':'─┬─]─┤
│ └─string─┘ └─'='─┘ │
└──────────────────────────────────<┘
the_params_at_last ●───┬─ [kwparams](kwparams)─────────────────────────┬──■
├─ [params](params)',' ✂ ─ [kwparams](kwparams)─┤
└─ [params](params)─────────────────────────────┘
paramdef ●───┬─'[' ✂ ─ >(the_params_at_last) ']'─┬──■
├─'(' ✂ ─ >(the_params_at_last) ')'─┤
└─'::' ✂ ─ [params](params)─────────┘
rule[Rule] ●─ [decorators](──┬→──────────┬──) [name](name) ✂ ───┬─→ >(paramdef) ─┬───┬─→'<' ✂ ─ [base](known_name)─┬───┬─'='──┬─ ✂ ─ [exp](expre)ENDRULE ✂ ──■
├→decorator─┤ └─→──────────────┘ └─→───────────────────────────┘ ├─':='─┤
└──────────<┘ └─':'──┘
ENDRULE ●───┬── &[UNINDENTED]──────┬──■
├─EMPTYLINE──┬─→';'─┬──┤
│ └─→────┘ │
├─⇥$ │
└─';'──────────────────┘
UNINDENTED ●─/(?=\s*(?:\r?\n|\r)[^\s])/──■
EMPTYLINE ●─/(?:\s*(?:\r?\n|\r)){2,}/──■
decorator ●─'@'─ !['@'] ✂ ─ @(──┬─'override'─┬─)─■
├─'name'─────┤
└─'nomemo'───┘
params ●─ @+(first_param)──┬→────────────────────────────┬───■
├→',' @+(literal)─ !['='] ✂ ──┤
└────────────────────────────<┘
first_param ●───┬─path────┬──■
└─literal─┘
kwparams ●───┬→────────────┬───■
├→',' ✂ ─pair─┤
└────────────<┘
pair ●─ @+(word)'=' ✂ ─ @+(literal)─■
expre ●───┬─choice───┬──■
└─sequence─┘
choice[Choice] ●───┬─→'|' ✂ ──┬─ @+(option)──┬─'|' ✂ ─ @+(option)─┬───■
└─→────────┘ └───────────────────<┘
option[Option] ●─ @(sequence)─■
sequence[Sequence] ●───┬── &[element',']──┬→───────────────┬───┬──■
│ ├→',' ✂ ─element─┤ │
│ └───────────────<┘ │
└───┬── ![ENDRULE]element─┬─────────────┘
└────────────────────<┘
element ●───┬─rule_include─┬──■
├─named────────┤
├─override─────┤
└─term─────────┘
rule_include[RuleInclude] ●─'>' ✂ ─ @(known_name)─■
named ●───┬─named_list───┬──■
└─named_single─┘
named_list[NamedList] ●─ [name](name)'+:' ✂ ─ [exp](term)─■
named_single[Named] ●─ [name](name)':' ✂ ─ [exp](term)─■
override ●───┬─override_list──────────────┬──■
├─override_single────────────┤
└─override_single_deprecated─┘
override_list[OverrideList] ●─'@+:' ✂ ─ @(term)─■
override_single[Override] ●─'@:' ✂ ─ @(term)─■
override_single_deprecated[Override] ●─'@' ✂ ─ @(term)─■
term ●───┬─void───────────────┬──■
├─gather─────────────┤
├─join───────────────┤
├─left_join──────────┤
├─right_join─────────┤
├─empty_closure──────┤
├─positive_closure───┤
├─closure────────────┤
├─optional───────────┤
├─skip_to────────────┤
├─lookahead──────────┤
├─negative_lookahead─┤
├─cut────────────────┤
├─cut_deprecated─────┤
└─atom───────────────┘
group[Group] ●─'(' ✂ ─ @(expre)')' ✂ ──■
gather ●── &[atom'.{'] ✂ ───┬─positive_gather─┬──■
└─normal_gather───┘
positive_gather[PositiveGather] ●─ [sep](atom)'.{' [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
normal_gather[Gather] ●─ [sep](atom)'.{' ✂ ─ [exp](expre)'}'──┬─→'*' ✂ ──┬─ ✂ ──■
└─→────────┘
join ●── &[atom'%{'] ✂ ───┬─positive_join─┬──■
└─normal_join───┘
positive_join[PositiveJoin] ●─ [sep](atom)'%{' [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
normal_join[Join] ●─ [sep](atom)'%{' ✂ ─ [exp](expre)'}'──┬─→'*' ✂ ──┬─ ✂ ──■
└─→────────┘
left_join[LeftJoin] ●─ [sep](atom)'<{' ✂ ─ [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
right_join[RightJoin] ●─ [sep](atom)'>{' ✂ ─ [exp](expre)'}'──┬─'+'─┬─ ✂ ──■
└─'-'─┘
positive_closure[PositiveClosure] ●───┬─'{' @(expre)'}'──┬─'-'─┬─ ✂ ──┬──■
│ └─'+'─┘ │
└─ @(atom)'+' ✂ ────────────────┘
closure[Closure] ●───┬─'{' @(expre)'}'──┬─→'*'─┬─ ✂ ──┬──■
│ └─→────┘ │
└─ @(atom)'*' ✂ ─────────────────┘
empty_closure[EmptyClosure] ●─'{}' ✂ ─ @( ∅ )─■
optional[Optional] ●───┬─'[' ✂ ─ @(expre)']' ✂ ──────────┬──■
└─ @(atom)─ ![──┬─'?"'─┬─]'?' ✂ ──┘
├─"?'"─┤
└─'?/'─┘
lookahead[Lookahead] ●─'&' ✂ ─ @(term)─■
negative_lookahead[NegativeLookahead] ●─'!' ✂ ─ @(term)─■
skip_to[SkipTo] ●─'->' ✂ ─ @(term)─■
atom ●───┬─group────┬──■
├─token────┤
├─alert────┤
├─constant─┤
├─call─────┤
├─pattern──┤
├─dot──────┤
└─eof──────┘
call[Call] ●─word─■
void[Void] ●─'()' ✂ ──■
fail[Fail] ●─'!()' ✂ ──■
cut[Cut] ●─'~' ✂ ──■
cut_deprecated[Cut] ●─'>>' ✂ ──■
known_name ●─name ✂ ──■
name ●─word─■
constant[Constant] ●── &['`']──┬─/(?ms)```((?:.|\n)*?)```/──┬──■
├─'`' @(literal)'`'──────────┤
└─/`(.*?)`/──────────────────┘
alert[Alert] ●─ [level](/\^+/─) [message](constant)─■
token[Token] ●───┬─string─────┬──■
└─raw_string─┘
literal ●───┬─string─────┬──■
├─raw_string─┤
├─boolean────┤
├─word───────┤
├─hex────────┤
├─float──────┤
├─int────────┤
└─null───────┘
string ●─STRING─■
raw_string ●─//─ @(STRING)─■
STRING ●───┬─ @(/"((?:[^"\n]|\\"|\\\\)*?)"/─) ✂ ─────┬──■
└─ @(/r"'((?:[^'\n]|\\'|\\\\)*?)'"/─) ✂ ──┘
hex ●─/0[xX](?:\d|[a-fA-F])+/──■
float ●─/[-+]?(?:\d+\.\d*|\d*\.\d+)(?:[Ee][-+]?\d+)?/──■
int ●─/[-+]?\d+/──■
path ●─/(?!\d)\w+(?:::(?!\d)\w+)+/──■
word ●─/(?!\d)\w+/──■
dot[Dot] ●─'/./'─■
pattern[Pattern] ●─regexes─■
regexes ●───┬→─────────────┬───■
├→'+' ✂ ─regex─┤
└─────────────<┘
regex ●───┬─'/' ✂ ─ @(/(?:[^/\\]|\\/|\\.)*/─)'/' ✂ ──┬──■
├─'?' @(STRING)────────────────────────────┤
└─deprecated_regex─────────────────────────┘
deprecated_regex ●─'?/' ✂ ─ @(/(?:.|\n)*?(?=/\?)/─)//\?+/─ ✂ ──■
boolean ●───┬─'True'──┬──■
└─'False'─┘
null ●─'None'─■
eof[EOF] ●─'$' ✂ ──■
.. _ANTLR: http://www.antlr.org/
.. _AST: http://en.wikipedia.org/wiki/Abstract_syntax_tree
.. _Abstract Syntax Tree: http://en.wikipedia.org/wiki/Abstract_syntax_tree
.. _Algol W: http://en.wikipedia.org/wiki/Algol_W
.. _Algorithms + Data Structures = Programs: http://www.amazon.com/Algorithms-Structures-Prentice-Hall-Automatic-Computation/dp/0130224189/
.. _BSD: http://en.wikipedia.org/wiki/BSD_licenses#2-clause_license_.28.22Simplified_BSD_License.22_or_.22FreeBSD_License.22.29
.. _Basel Shishani: https://bitbucket.org/basel-shishani
.. _C: http://en.wikipedia.org/wiki/C_language
.. _CHANGELOG: https://github.com/neogeny/TatSu/releases
.. _CSAIL at MIT: http://www.csail.mit.edu/
.. _Cyclomatic complexity: http://en.wikipedia.org/wiki/Cyclomatic_complexity
.. _David Röthlisberger: https://bitbucket.org/drothlis/
.. _Dennis Ritchie: http://en.wikipedia.org/wiki/Dennis_Ritchie
.. _EBNF: http://en.wikipedia.org/wiki/Ebnf
.. _ISO EBNF: http://en.wikipedia.org/wiki/Ebnf
.. _English: http://en.wikipedia.org/wiki/English_grammar
.. _Euler: http://en.wikipedia.org/wiki/Euler_programming_language
.. _Grako: https://bitbucket.org/neogeny/grako/
.. _Jack: http://en.wikipedia.org/wiki/Javacc
.. _Japanese: http://en.wikipedia.org/wiki/Japanese_grammar
.. _KLOC: http://en.wikipedia.org/wiki/KLOC
.. _Kathryn Long: https://bitbucket.org/starkat
.. _Keywords: https://en.wikipedia.org/wiki/Reserved_word
.. _`left-recursive`: https://en.wikipedia.org/wiki/Left_recursion
.. _LL(1): http://en.wikipedia.org/wiki/LL(1)
.. _Marcus Brinkmann: http://blog.marcus-brinkmann.de/
.. _MediaWiki: http://www.mediawiki.org/wiki/MediaWiki
.. _Modula-2: http://en.wikipedia.org/wiki/Modula-2
.. _Modula: http://en.wikipedia.org/wiki/Modula
.. _Oberon-2: http://en.wikipedia.org/wiki/Oberon-2
.. _Oberon: http://en.wikipedia.org/wiki/Oberon_(programming_language)
.. _PEG and Packrat parsing mailing list: https://lists.csail.mit.edu/mailman/listinfo/peg
.. _PEG.js: http://pegjs.majda.cz/
.. _PEG: http://en.wikipedia.org/wiki/Parsing_expression_grammar
.. _PL/0: http://en.wikipedia.org/wiki/PL/0
.. _Packrat: http://bford.info/packrat/
.. _Pascal: http://en.wikipedia.org/wiki/Pascal_programming_language
.. _Paul Sargent: https://bitbucket.org/PaulS/
.. _Perl: http://www.perl.org/
.. _PyPy team: http://pypy.org/people.html
.. _PyPy: http://pypy.org/
.. _Python Weekly: http://www.pythonweekly.com/
.. _Python: http://python.org
.. _Reserved Words: https://en.wikipedia.org/wiki/Reserved_word
.. _Robert Speer: https://bitbucket.org/r_speer
.. _Ruby: http://www.ruby-lang.org/
.. _Semantic Graph: http://en.wikipedia.org/wiki/Abstract_semantic_graph
.. _StackOverflow: http://stackoverflow.com/tags/tatsu/info
.. _Sublime Text: https://www.sublimetext.com
.. _TatSu Forum: https://groups.google.com/forum/?fromgroups#!forum/tatsu
.. _UCAB: http://www.ucab.edu.ve/
.. _USB: http://www.usb.ve/
.. _Unix: http://en.wikipedia.org/wiki/Unix
.. _VIM: http://www.vim.org/
.. _WTK: http://en.wikipedia.org/wiki/Well-known_text
.. _Warth et al: http://www.vpri.org/pdf/tr2007002_packrat.pdf
.. _Well-known text: http://en.wikipedia.org/wiki/Well-known_text
.. _Wirth: http://en.wikipedia.org/wiki/Niklaus_Wirth
.. _`LICENSE`: LICENSE
.. _basel-shishani: https://bitbucket.org/basel-shishani
.. _blog post: http://dietbuddha.blogspot.com/2012/12/52python-encapsulating-exceptions-with.html
.. _context managers: http://docs.python.org/2/library/contextlib.html
.. _declensions: http://en.wikipedia.org/wiki/Declension
.. _drothlis: https://bitbucket.org/drothlis
.. _email: mailto:apalala@gmail.com
.. _exceptions: http://www.jeffknupp.com/blog/2013/02/06/write-cleaner-python-use-exceptions/
.. _franz\_g: https://bitbucket.org/franz_g
.. _gapag: https://bitbucket.org/gapag
.. _gegenschall: https://bitbucket.org/gegenschall
.. _gkimbar: https://bitbucket.org/gkimbar
.. _introduced: http://dl.acm.org/citation.cfm?id=964001.964011
.. _jimon: https://bitbucket.org/jimon
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