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438 lines
15 KiB
Python
438 lines
15 KiB
Python
# Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
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# Licensed to PSF under a Contributor Agreement.
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# Modifications:
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# Copyright David Halter and Contributors
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# Modifications are dual-licensed: MIT and PSF.
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"""
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Specifying grammars in pgen is possible with this grammar::
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grammar: (NEWLINE | rule)* ENDMARKER
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rule: NAME ':' rhs NEWLINE
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rhs: items ('|' items)*
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items: item+
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item: '[' rhs ']' | atom ['+' | '*']
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atom: '(' rhs ')' | NAME | STRING
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This grammar is self-referencing.
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"""
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from parso.pgen2.grammar import Grammar
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from parso.python import token
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from parso.python import tokenize
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from parso.utils import parse_version_string
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class ParserGenerator(object):
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def __init__(self, dfas, token_namespace):
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self._token_namespace = token_namespace
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self.dfas = dfas
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def make_grammar(self, grammar):
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self._first = {} # map from symbol name to set of tokens
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self._addfirstsets()
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names = list(self.dfas.keys())
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names.sort()
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for name in names:
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i = 256 + len(grammar.symbol2number)
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grammar.symbol2number[name] = i
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grammar.number2symbol[i] = name
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for name in names:
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dfa = self.dfas[name]
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states = []
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for state in dfa:
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arcs = []
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for label, next in state.arcs.items():
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arcs.append((self._make_label(grammar, label), dfa.index(next)))
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if state.isfinal:
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arcs.append((0, dfa.index(state)))
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states.append(arcs)
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grammar.states.append(states)
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grammar.dfas[grammar.symbol2number[name]] = (states, self._make_first(grammar, name))
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return grammar
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def _make_first(self, grammar, name):
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rawfirst = self._first[name]
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first = {}
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for label in rawfirst:
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ilabel = self._make_label(grammar, label)
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##assert ilabel not in first # XXX failed on <> ... !=
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first[ilabel] = 1
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return first
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def _make_label(self, grammar, label):
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# XXX Maybe this should be a method on a subclass of converter?
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ilabel = len(grammar.labels)
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if label[0].isalpha():
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# Either a symbol name or a named token
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if label in grammar.symbol2number:
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# A symbol name (a non-terminal)
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if label in grammar.symbol2label:
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return grammar.symbol2label[label]
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else:
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grammar.labels.append((grammar.symbol2number[label], None))
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grammar.symbol2label[label] = ilabel
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grammar.label2symbol[ilabel] = label
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return ilabel
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else:
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# A named token (NAME, NUMBER, STRING)
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itoken = getattr(self._token_namespace, label, None)
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assert isinstance(itoken, int), label
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if itoken in grammar.tokens:
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return grammar.tokens[itoken]
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else:
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grammar.labels.append((itoken, None))
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grammar.tokens[itoken] = ilabel
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return ilabel
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else:
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# Either a keyword or an operator
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assert label[0] in ('"', "'"), label
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value = eval(label)
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if value[0].isalpha():
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# A keyword
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if value in grammar.keywords:
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return grammar.keywords[value]
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else:
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# TODO this might be an issue?! Using token.NAME here?
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grammar.labels.append((token.NAME, value))
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grammar.keywords[value] = ilabel
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return ilabel
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else:
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# An operator (any non-numeric token)
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itoken = self._token_namespace.generate_token_id(value)
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if itoken in grammar.tokens:
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return grammar.tokens[itoken]
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else:
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grammar.labels.append((itoken, None))
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grammar.tokens[itoken] = ilabel
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return ilabel
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def _addfirstsets(self):
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names = list(self.dfas.keys())
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names.sort()
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for name in names:
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if name not in self._first:
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self._calcfirst(name)
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#print name, self._first[name].keys()
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def _calcfirst(self, name):
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dfa = self.dfas[name]
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self._first[name] = None # dummy to detect left recursion
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state = dfa[0]
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totalset = {}
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overlapcheck = {}
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for label, next in state.arcs.items():
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if label in self.dfas:
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if label in self._first:
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fset = self._first[label]
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if fset is None:
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raise ValueError("recursion for rule %r" % name)
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else:
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self._calcfirst(label)
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fset = self._first[label]
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totalset.update(fset)
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overlapcheck[label] = fset
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else:
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totalset[label] = 1
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overlapcheck[label] = {label: 1}
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inverse = {}
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for label, itsfirst in overlapcheck.items():
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for symbol in itsfirst:
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if symbol in inverse:
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raise ValueError("rule %s is ambiguous; %s is in the"
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" first sets of %s as well as %s" %
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(name, symbol, label, inverse[symbol]))
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inverse[symbol] = label
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self._first[name] = totalset
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class _GrammarParser():
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"""
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The parser for Python grammar files.
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"""
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def __init__(self, bnf_grammar):
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self._bnf_grammar = bnf_grammar
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self.generator = tokenize.tokenize(
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bnf_grammar,
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version_info=parse_version_string('3.6')
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)
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self._gettoken() # Initialize lookahead
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def parse(self):
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# grammar: (NEWLINE | rule)* ENDMARKER
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while self.type != token.ENDMARKER:
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while self.type == token.NEWLINE:
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self._gettoken()
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# rule: NAME ':' rhs NEWLINE
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self._current_rule_name = self._expect(token.NAME)
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self._expect(token.COLON)
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a, z = self._parse_rhs()
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self._expect(token.NEWLINE)
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yield a, z
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def _parse_rhs(self):
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# rhs: items ('|' items)*
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a, z = self._parse_items()
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if self.value != "|":
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return a, z
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else:
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aa = NFAState(self._current_rule_name)
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zz = NFAState(self._current_rule_name)
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while True:
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# Add the possibility to go into the state of a and come back
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# to finish.
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aa.add_arc(a)
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z.add_arc(zz)
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if self.value != "|":
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break
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self._gettoken()
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a, z = self._parse_items()
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return aa, zz
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def _parse_items(self):
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# items: item+
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a, b = self._parse_item()
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while self.type in (token.NAME, token.STRING, token.LPAR, token.LSQB):
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c, d = self._parse_item()
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# Need to end on the next item.
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b.add_arc(c)
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b = d
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return a, b
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def _parse_item(self):
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# item: '[' rhs ']' | atom ['+' | '*']
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if self.value == "[":
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self._gettoken()
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a, z = self._parse_rhs()
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self._expect(token.RSQB)
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# Make it also possible that there is no token and change the
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# state.
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a.add_arc(z)
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return a, z
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else:
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a, z = self._parse_atom()
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value = self.value
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if value not in ("+", "*"):
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return a, z
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self._gettoken()
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# Make it clear that we can go back to the old state and repeat.
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z.add_arc(a)
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if value == "+":
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return a, z
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else:
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# The end state is the same as the beginning, nothing must
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# change.
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return a, a
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def _parse_atom(self):
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# atom: '(' rhs ')' | NAME | STRING
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if self.value == "(":
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self._gettoken()
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a, z = self._parse_rhs()
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self._expect(token.RPAR)
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return a, z
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elif self.type in (token.NAME, token.STRING):
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a = NFAState(self._current_rule_name)
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z = NFAState(self._current_rule_name)
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# Make it clear that the state transition requires that value.
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a.add_arc(z, self.value)
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self._gettoken()
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return a, z
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else:
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self._raise_error("expected (...) or NAME or STRING, got %s/%s",
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self.type, self.value)
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def _expect(self, type):
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if self.type != type:
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self._raise_error("expected %s(%s), got %s(%s)",
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type, token.tok_name[type], self.type, self.value)
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value = self.value
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self._gettoken()
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return value
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def _gettoken(self):
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tup = next(self.generator)
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self.type, self.value, self.begin, prefix = tup
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def _raise_error(self, msg, *args):
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if args:
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try:
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msg = msg % args
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except:
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msg = " ".join([msg] + list(map(str, args)))
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line = self._bnf_grammar.splitlines()[self.begin[0] - 1]
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raise SyntaxError(msg, ('<grammar>', self.begin[0],
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self.begin[1], line))
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class NFAState(object):
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def __init__(self, from_rule):
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self.from_rule = from_rule
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self.arcs = [] # list of (label, NFAState) pairs
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def add_arc(self, next, label=None):
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assert label is None or isinstance(label, str)
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assert isinstance(next, NFAState)
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self.arcs.append((label, next))
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def __repr__(self):
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return '<%s: from %s>' % (self.__class__.__name__, self.from_rule)
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class DFAState(object):
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def __init__(self, nfaset, final):
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assert isinstance(nfaset, dict)
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assert isinstance(next(iter(nfaset)), NFAState)
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assert isinstance(final, NFAState)
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self.nfaset = nfaset
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self.isfinal = final in nfaset
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self.arcs = {} # map from label to DFAState
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def add_arc(self, next, label):
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assert isinstance(label, str)
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assert label not in self.arcs
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assert isinstance(next, DFAState)
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self.arcs[label] = next
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def unifystate(self, old, new):
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for label, next in self.arcs.items():
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if next is old:
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self.arcs[label] = new
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def __eq__(self, other):
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# Equality test -- ignore the nfaset instance variable
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assert isinstance(other, DFAState)
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if self.isfinal != other.isfinal:
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return False
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# Can't just return self.arcs == other.arcs, because that
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# would invoke this method recursively, with cycles...
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if len(self.arcs) != len(other.arcs):
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return False
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for label, next in self.arcs.items():
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if next is not other.arcs.get(label):
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return False
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return True
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__hash__ = None # For Py3 compatibility.
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def _simplify_dfa(dfas):
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# This is not theoretically optimal, but works well enough.
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# Algorithm: repeatedly look for two states that have the same
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# set of arcs (same labels pointing to the same nodes) and
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# unify them, until things stop changing.
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# dfas is a list of DFAState instances
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changes = True
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while changes:
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changes = False
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for i, state_i in enumerate(dfas):
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for j in range(i + 1, len(dfas)):
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state_j = dfas[j]
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if state_i == state_j:
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#print " unify", i, j
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del dfas[j]
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for state in dfas:
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state.unifystate(state_j, state_i)
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changes = True
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break
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def _make_dfa(start, finish):
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# To turn an NFA into a DFA, we define the states of the DFA
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# to correspond to *sets* of states of the NFA. Then do some
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# state reduction. Let's represent sets as dicts with 1 for
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# values.
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assert isinstance(start, NFAState)
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assert isinstance(finish, NFAState)
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def closure(state):
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base = {}
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addclosure(state, base)
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return base
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def addclosure(state, base):
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assert isinstance(state, NFAState)
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if state in base:
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return
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base[state] = 1
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for label, next in state.arcs:
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if label is None:
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addclosure(next, base)
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states = [DFAState(closure(start), finish)]
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for state in states: # NB states grows while we're iterating
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arcs = {}
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for nfastate in state.nfaset:
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for label, next in nfastate.arcs:
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if label is not None:
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addclosure(next, arcs.setdefault(label, {}))
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for label, nfaset in arcs.items():
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for st in states:
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if st.nfaset == nfaset:
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break
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else:
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st = DFAState(nfaset, finish)
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states.append(st)
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state.add_arc(st, label)
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return states # List of DFAState instances; first one is start
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def _dump_nfa(start, finish):
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print("Dump of NFA for", start.from_rule)
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todo = [start]
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for i, state in enumerate(todo):
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print(" State", i, state is finish and "(final)" or "")
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for label, next in state.arcs:
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if next in todo:
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j = todo.index(next)
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else:
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j = len(todo)
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todo.append(next)
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if label is None:
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print(" -> %d" % j)
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else:
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print(" %s -> %d" % (label, j))
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def _dump_dfa(name, dfa):
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print("Dump of DFA for", name)
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for i, state in enumerate(dfa):
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print(" State", i, state.isfinal and "(final)" or "")
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for label, next in state.arcs.items():
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print(" %s -> %d" % (label, dfa.index(next)))
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def generate_grammar(bnf_grammar, token_namespace):
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"""
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``bnf_text`` is a grammar in extended BNF (using * for repetition, + for
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at-least-once repetition, [] for optional parts, | for alternatives and ()
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for grouping).
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It's not EBNF according to ISO/IEC 14977. It's a dialect Python uses in its
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own parser.
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"""
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dfas = {}
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start_symbol = None
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for a, z in _GrammarParser(bnf_grammar).parse():
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#_dump_nfa(a, z)
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dfa = _make_dfa(a, z)
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#_dump_dfa(self._current_rule_name, dfa)
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# oldlen = len(dfa)
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_simplify_dfa(dfa)
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# newlen = len(dfa)
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dfas[a.from_rule] = dfa
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#print(self._current_rule_name, oldlen, newlen)
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if start_symbol is None:
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start_symbol = a.from_rule
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p = ParserGenerator(dfas, token_namespace)
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return p.make_grammar(Grammar(bnf_grammar, start_symbol))
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