PEP 617: Resolve unreferenced footnotes (#3250)
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pep-0617.rst
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pep-0617.rst
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@ -1,7 +1,5 @@
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PEP: 617
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Title: New PEG parser for CPython
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Version: $Revision$
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Last-Modified: $Date$
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Author: Guido van Rossum <guido@python.org>,
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Pablo Galindo <pablogsal@python.org>,
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Lysandros Nikolaou <lisandrosnik@gmail.com>
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@ -13,6 +11,8 @@ Created: 24-Mar-2020
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Python-Version: 3.9
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Post-History: 02-Apr-2020
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.. highlight:: PEG
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========
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Overview
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========
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@ -40,7 +40,7 @@ and the *follow sets* of the grammar:
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* Given a rule, the *first set* is the collection of all terminals that can occur
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first in a full derivation of that rule. Intuitively, this helps the parser decide
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among the alternatives in a rule. For
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instance, given the rule ::
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instance, given the rule::
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rule: A | B
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@ -298,13 +298,13 @@ and "hidden left-recursion" like::
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Syntax
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------
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The grammar consists of a sequence of rules of the form: ::
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The grammar consists of a sequence of rules of the form::
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rule_name: expression
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Optionally, a type can be included right after the rule name, which
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specifies the return type of the C or Python function corresponding to
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the rule: ::
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the rule::
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rule_name[return_type]: expression
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@ -324,7 +324,7 @@ Python-style comments.
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Match e1, then match e2.
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::
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.. code:: PEG
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rule_name: first_rule second_rule
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@ -339,7 +339,7 @@ The first alternative can also appear on the line after the rule name
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for formatting purposes. In that case, a \| must be used before the
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first alternative, like so:
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::
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.. code:: PEG
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rule_name[return_type]:
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| first_alt
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@ -350,14 +350,14 @@ first alternative, like so:
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Match e.
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::
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.. code:: PEG
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rule_name: (e)
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A slightly more complex and useful example includes using the grouping
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operator together with the repeat operators:
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::
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.. code:: PEG
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rule_name: (e1 e2)*
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@ -366,14 +366,14 @@ operator together with the repeat operators:
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Optionally match e.
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::
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.. code:: PEG
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rule_name: [e]
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A more useful example includes defining that a trailing comma is
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optional:
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::
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.. code:: PEG
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rule_name: e (',' e)* [',']
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@ -384,7 +384,7 @@ optional:
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Match zero or more occurrences of e.
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::
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.. code:: PEG
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rule_name: (e1 e2)*
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@ -395,7 +395,7 @@ Match zero or more occurrences of e.
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Match one or more occurrences of e.
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::
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.. code:: PEG
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rule_name: (e1 e2)+
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@ -406,7 +406,7 @@ Match one or more occurrences of e, separated by s. The generated parse
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tree does not include the separator. This is otherwise identical to
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``(e (s e)*)``.
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::
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.. code:: PEG
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rule_name: ','.e+
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@ -428,7 +428,7 @@ An example taken from the proposed Python grammar specifies that a primary
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consists of an atom, which is not followed by a ``.`` or a ``(`` or a
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``[``:
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::
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.. code:: PEG
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primary: atom !'.' !'(' !'['
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@ -439,7 +439,7 @@ consists of an atom, which is not followed by a ``.`` or a ``(`` or a
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Commit to the current alternative, even if it fails to parse.
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::
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.. code:: PEG
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rule_name: '(' ~ some_rule ')' | some_alt
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@ -451,7 +451,7 @@ Variables in the Grammar
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~~~~~~~~~~~~~~~~~~~~~~~~
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A subexpression can be named by preceding it with an identifier and an
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``=`` sign. The name can then be used in the action (see below), like this: ::
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``=`` sign. The name can then be used in the action (see below), like this::
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rule_name[return_type]: '(' a=some_other_rule ')' { a }
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@ -469,7 +469,7 @@ files should be written, each one with a different set of actions, keeping
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everything else apart from said actions identical in both files. As an
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example of a grammar with Python actions, the piece of the parser generator
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that parses grammar files is bootstrapped from a meta-grammar file with
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Python actions that generate the grammar tree as a result of the parsing.
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Python actions that generate the grammar tree as a result of the parsing.
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In the specific case of the new proposed PEG grammar for Python, having
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actions allows directly describing how the AST is composed in the grammar
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@ -496,7 +496,7 @@ with all the parsed expressions gets returned (this is meant for debugging).
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The full meta-grammar for the grammars supported by the PEG generator is:
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::
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.. code:: PEG
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start[Grammar]: grammar ENDMARKER { grammar }
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@ -589,25 +589,25 @@ As an illustrative example this simple grammar file allows directly
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generating a full parser that can parse simple arithmetic expressions and that
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returns a valid C-based Python AST:
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::
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.. code:: PEG
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start[mod_ty]: a=expr_stmt* $ { Module(a, NULL, p->arena) }
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expr_stmt[stmt_ty]: a=expr NEWLINE { _Py_Expr(a, EXTRA) }
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expr[expr_ty]:
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expr[expr_ty]:
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| l=expr '+' r=term { _Py_BinOp(l, Add, r, EXTRA) }
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| l=expr '-' r=term { _Py_BinOp(l, Sub, r, EXTRA) }
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| t=term { t }
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term[expr_ty]:
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term[expr_ty]:
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| l=term '*' r=factor { _Py_BinOp(l, Mult, r, EXTRA) }
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| l=term '/' r=factor { _Py_BinOp(l, Div, r, EXTRA) }
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| f=factor { f }
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factor[expr_ty]:
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factor[expr_ty]:
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| '(' e=expr ')' { e }
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| a=atom { a }
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atom[expr_ty]:
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atom[expr_ty]:
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| n=NAME { n }
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| n=NUMBER { n }
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| s=STRING { s }
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@ -619,7 +619,7 @@ for the parser.
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A similar grammar written to target Python AST objects:
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::
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.. code:: PEG
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start: expr NEWLINE? ENDMARKER { ast.Expression(expr) }
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expr:
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@ -787,17 +787,16 @@ References
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==========
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.. [1] Ford, Bryan
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http://pdos.csail.mit.edu/~baford/packrat/thesis
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https://pdos.csail.mit.edu/~baford/packrat/thesis/
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.. [2] Medeiros et al.
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https://arxiv.org/pdf/1207.0443.pdf
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.. [3] Warth et al.
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http://web.cs.ucla.edu/~todd/research/pepm08.pdf
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https://web.cs.ucla.edu/~todd/research/pepm08.pdf
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.. [#GUIDO_PEG]
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Guido's series on PEG parsing
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https://medium.com/@gvanrossum_83706/peg-parsing-series-de5d41b2ed60
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[4] Guido's series on PEG parsing
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\ https://medium.com/@gvanrossum_83706/peg-parsing-series-de5d41b2ed60
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=========
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Copyright
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