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.. include:: links.rst
Grammar Directives
------------------
|TatSu| allows *directives* in the grammar that control the behavior of the generated parsers. All directives are of the form ``@@name :: <value>``. For example:
.. code::
@@ignorecase :: True
The *directives* supported by |TatSu| are described below.
``@@grammar :: <word>``
~~~~~~~~~~~~~~~~~~~~~~~
Specifies the name of the grammar, and provides the base name for the classes in parser source-code generation.
``@@comments :: <regexp>``
~~~~~~~~~~~~~~~~~~~~~~~~~~
Specifies a regular expression to identify and exclude inline (bracketed) comments before the text is scanned by the parser. For ``(* ... *)`` comments:
.. code::
@@comments :: /\(\*((?:.|\n)*?)\*\)/
.. note::
In previous versions of |TatSu|, the `re.MULTILINE <https://docs.python .org/3/library/re.html#re.MULTILINE>`_
option was enabled by default. This is no longer the case. Use ``(?m)`` at the start of your
regular expressions to make them multi-line.
``@@eol_comments :: <regexp>``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Specifies a regular expression to identify and exclude end-of-line comments before the text is scanned by the parser. For ``# ...`` comments:
.. code::
@@eol_comments :: /#([^\n]*?)$/
.. note::
In previous versions of |TatSu|, the `re.MULTILINE <https://docs.python .org/3/library/re.html#re.MULTILINE>`_
option was enabled by default. This is no longer the case. Use ``(?m)`` at the start of your
regular expressions to make them multi-line.
``@@ignorecase :: <bool>``
~~~~~~~~~~~~~~~~~~~~~~~~~~
If set to ``True`` makes |TatSu| not consider case when parsing tokens. Defaults to ``False``:
.. code::
@@ignorecase :: True
``@@keyword :: {<word>|<string>}+``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Specifies the list of strings or words that the grammar should consider as *"keywords"*.
May appear more than once. See the `Reserved Words and Keywords`_ section for an explanation.
.. _`Reserved Words and Keywords`: syntax.html#reserved-words-and-keywords
``@@left_recursion :: <bool>``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enables left-recursive rules in the grammar. See the `Left Recursion`_ sections for an explanation.
.. _`Left Recursion`: left_recursion.html
``@@namechars :: <string>``
~~~~~~~~~~~~~~~~~~~~~~~~~~~
A list of (non-alphanumeric) characters that should be considered part of names when using the `@@nameguard`_ feature:
.. code::
@@namechars :: '-_$'
.. _`@@nameguard`: #nameguard-bool
``@@nameguard :: <bool>``
~~~~~~~~~~~~~~~~~~~~~~~~~
When set to ``True``, avoids matching tokens when the next character in the input sequence is alphanumeric or a ``@@namechar``. Defaults to ``True``. See the `'text' expression`_ for an explanation.
.. code::
@@nameguard :: False
.. _`'text' expression`: syntax.html?highlight=nameguard#text-or-text
``@@parseinfo :: <bool>``
~~~~~~~~~~~~~~~~~~~~~~~~~
When ``True``, the parser will add parse information to every ``AST`` and ``Node`` generated by the parse under a ``parseinfo`` field. The information will include:
* ``rule`` the rule name that parsed the node
* ``pos`` the initial position for the node in the input
* ``endpos`` the final position for the node in the input
* ``line`` the initial input line number for the element
* ``endline`` the final line number for the element
Enabling ``@@parseinfo`` will allow precise reporting over the input source-code while performing semantic actions.
``@@whitespace :: <regexp>``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Provides a regular expression for the whitespace to be ignored by the parser. If no definition is
provided, then ``r'(?m)\s+'`` will be used as default:
.. code::
@@whitespace :: /[\t ]+/
To disable any parsing of whitespace, use ``None`` for the definition:
.. code::
@@whitespace :: None
.. note::
In previous versions of |TatSu|, the `re.MULTILINE <https://docs.python .org/3/library/re.html#re.MULTILINE>`_
option was enabled by default. This is no longer the case. Use ``(?m)`` at the start of your
regular expressions to make them multi-line.
|
