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Commitec90d40

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encukoublaisep
andcommitted
Consolidate with the Full Grammar intro
Co-authored-by: Blaise Pabon <blaise@gmail.com>
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‎Doc/reference/grammar.rst

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@@ -8,15 +8,13 @@ used to generate the CPython parser (see :source:`Grammar/python.gram`).
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The version here omits details related to code generation and
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error recovery.
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The notation is a mixture of `EBNF
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<https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form>`_
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and `PEG<https://en.wikipedia.org/wiki/Parsing_expression_grammar>`_.
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In particular, ``&`` followed by a symbol, token or parenthesized
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group indicates a positive lookahead (i.e., is required to match but
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not consumed), while ``!`` indicates a negative lookahead (i.e., is
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required *not* to match). We use the ``|`` separator to mean PEG's
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"ordered choice" (written as ``/`` in traditional PEG grammars). See
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:pep:`617` for more details on the grammar's syntax.
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The notation used here is the same as in the preceding docs,
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and is described in the:ref:`notation<notation>` section,
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except for a few extra complications:
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* ``&e``: a positive lookahead (that is, ``e`` is required to match but
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not consumed)
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* ``!e``: a negative lookahead (that is, ``e`` is required *not* to match)
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..literalinclude::../../Grammar/python.gram
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:language: peg

‎Doc/reference/introduction.rst

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@@ -90,9 +90,10 @@ Notation
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..index::BNF, grammar, syntax, notation
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The descriptions of lexical analysis and syntax use a modified
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`Backus–Naur form (BNF)<https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form>`_ grammar
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notation. This uses the following style of definition:
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The descriptions of lexical analysis use a grammar notation that is a mixture
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of `EBNF<https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form>`_
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and `PEG<https://en.wikipedia.org/wiki/Parsing_expression_grammar>`_.
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For example:
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..grammar-snippet::
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:group: notation
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* ``e1 e2``: Items separated only by whitespace denote a sequence.
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Here, ``e1`` must be followed by ``e2``.
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* ``e1 | e2``: A vertical bar is used to separate alternatives.
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It is the least tightly binding operator in this notation.
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It denotes PEG's "ordered choice": if ``e1`` matches, ``e2`` is
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not considered.
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In traditional PEG grammars, this is written as a slash, ``/``, rather than
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a vertical bar.
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See:pep:`617` for more background and details.
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* ``e*``: A star means zero or more repetitions of the preceding item.
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* ``e+``: Likewise, a plus means one or more repetitions.
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* ``[e]``: A phrase enclosed in square brackets means zero or
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the preceding item is optional.
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* ``(e)``: Parentheses are used for grouping.
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The unary operators (``*``, ``+``, ``?``) bind as tightly as possible.
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The unary operators (``*``, ``+``, ``?``) bind as tightly as possible;
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the vertical bar (``|``) binds most loosely.
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White space is only meaningful to separate tokens.
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