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pgen2
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pgen.py
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# Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved. # Licensed to PSF under a Contributor Agreement. # Pgen imports from . import grammar, token, tokenize class PgenGrammar(grammar.Grammar): pass class ParserGenerator(object): def __init__(self, filename, stream=None): close_stream = None if stream is None: stream = open(filename) close_stream = stream.close self.filename = filename self.stream = stream self.generator = tokenize.generate_tokens(stream.readline) self.gettoken() # Initialize lookahead self.dfas, self.startsymbol = self.parse() if close_stream is not None: close_stream() self.first = {} # map from symbol name to set of tokens self.addfirstsets() def make_grammar(self): c = PgenGrammar() names = list(self.dfas.keys()) names.sort() names.remove(self.startsymbol) names.insert(0, self.startsymbol) for name in names: i = 256 + len(c.symbol2number) c.symbol2number[name] = i c.number2symbol[i] = name for name in names: dfa = self.dfas[name] states = [] for state in dfa: arcs = [] for label, next in sorted(state.arcs.items()): arcs.append((self.make_label(c, label), dfa.index(next))) if state.isfinal: arcs.append((0, dfa.index(state))) states.append(arcs) c.states.append(states) c.dfas[c.symbol2number[name]] = (states, self.make_first(c, name)) c.start = c.symbol2number[self.startsymbol] return c def make_first(self, c, name): rawfirst = self.first[name] first = {} for label in sorted(rawfirst): ilabel = self.make_label(c, label) ##assert ilabel not in first # XXX failed on <> ... != first[ilabel] = 1 return first def make_label(self, c, label): # XXX Maybe this should be a method on a subclass of converter? ilabel = len(c.labels) if label[0].isalpha(): # Either a symbol name or a named token if label in c.symbol2number: # A symbol name (a non-terminal) if label in c.symbol2label: return c.symbol2label[label] else: c.labels.append((c.symbol2number[label], None)) c.symbol2label[label] = ilabel return ilabel else: # A named token (NAME, NUMBER, STRING) itoken = getattr(token, label, None) assert isinstance(itoken, int), label assert itoken in token.tok_name, label if itoken in c.tokens: return c.tokens[itoken] else: c.labels.append((itoken, None)) c.tokens[itoken] = ilabel return ilabel else: # Either a keyword or an operator assert label[0] in ('"', "'"), label value = eval(label) if value[0].isalpha(): # A keyword if value in c.keywords: return c.keywords[value] else: c.labels.append((token.NAME, value)) c.keywords[value] = ilabel return ilabel else: # An operator (any non-numeric token) itoken = grammar.opmap[value] # Fails if unknown token if itoken in c.tokens: return c.tokens[itoken] else: c.labels.append((itoken, None)) c.tokens[itoken] = ilabel return ilabel def addfirstsets(self): names = list(self.dfas.keys()) names.sort() for name in names: if name not in self.first: self.calcfirst(name) #print name, self.first[name].keys() def calcfirst(self, name): dfa = self.dfas[name] self.first[name] = None # dummy to detect left recursion state = dfa[0] totalset = {} overlapcheck = {} for label, next in state.arcs.items(): if label in self.dfas: if label in self.first: fset = self.first[label] if fset is None: raise ValueError("recursion for rule %r" % name) else: self.calcfirst(label) fset = self.first[label] totalset.update(fset) overlapcheck[label] = fset else: totalset[label] = 1 overlapcheck[label] = {label: 1} inverse = {} for label, itsfirst in overlapcheck.items(): for symbol in itsfirst: if symbol in inverse: raise ValueError("rule %s is ambiguous; %s is in the" " first sets of %s as well as %s" % (name, symbol, label, inverse[symbol])) inverse[symbol] = label self.first[name] = totalset def parse(self): dfas = {} startsymbol = None # MSTART: (NEWLINE | RULE)* ENDMARKER while self.type != token.ENDMARKER: while self.type == token.NEWLINE: self.gettoken() # RULE: NAME ':' RHS NEWLINE name = self.expect(token.NAME) self.expect(token.OP, ":") a, z = self.parse_rhs() self.expect(token.NEWLINE) #self.dump_nfa(name, a, z) dfa = self.make_dfa(a, z) #self.dump_dfa(name, dfa) oldlen = len(dfa) self.simplify_dfa(dfa) newlen = len(dfa) dfas[name] = dfa #print name, oldlen, newlen if startsymbol is None: startsymbol = name return dfas, startsymbol def make_dfa(self, start, finish): # To turn an NFA into a DFA, we define the states of the DFA # to correspond to *sets* of states of the NFA. Then do some # state reduction. Let's represent sets as dicts with 1 for # values. assert isinstance(start, NFAState) assert isinstance(finish, NFAState) def closure(state): base = {} addclosure(state, base) return base def addclosure(state, base): assert isinstance(state, NFAState) if state in base: return base[state] = 1 for label, next in state.arcs: if label is None: addclosure(next, base) states = [DFAState(closure(start), finish)] for state in states: # NB states grows while we're iterating arcs = {} for nfastate in state.nfaset: for label, next in nfastate.arcs: if label is not None: addclosure(next, arcs.setdefault(label, {})) for label, nfaset in sorted(arcs.items()): for st in states: if st.nfaset == nfaset: break else: st = DFAState(nfaset, finish) states.append(st) state.addarc(st, label) return states # List of DFAState instances; first one is start def dump_nfa(self, name, start, finish): print("Dump of NFA for", name) todo = [start] for i, state in enumerate(todo): print(" State", i, state is finish and "(final)" or "") for label, next in state.arcs: if next in todo: j = todo.index(next) else: j = len(todo) todo.append(next) if label is None: print(" -> %d" % j) else: print(" %s -> %d" % (label, j)) def dump_dfa(self, name, dfa): print("Dump of DFA for", name) for i, state in enumerate(dfa): print(" State", i, state.isfinal and "(final)" or "") for label, next in sorted(state.arcs.items()): print(" %s -> %d" % (label, dfa.index(next))) def simplify_dfa(self, dfa): # This is not theoretically optimal, but works well enough. # Algorithm: repeatedly look for two states that have the same # set of arcs (same labels pointing to the same nodes) and # unify them, until things stop changing. # dfa is a list of DFAState instances changes = True while changes: changes = False for i, state_i in enumerate(dfa): for j in range(i+1, len(dfa)): state_j = dfa[j] if state_i == state_j: #print " unify", i, j del dfa[j] for state in dfa: state.unifystate(state_j, state_i) changes = True break def parse_rhs(self): # RHS: ALT ('|' ALT)* a, z = self.parse_alt() if self.value != "|": return a, z else: aa = NFAState() zz = NFAState() aa.addarc(a) z.addarc(zz) while self.value == "|": self.gettoken() a, z = self.parse_alt() aa.addarc(a) z.addarc(zz) return aa, zz def parse_alt(self): # ALT: ITEM+ a, b = self.parse_item() while (self.value in ("(", "[") or self.type in (token.NAME, token.STRING)): c, d = self.parse_item() b.addarc(c) b = d return a, b def parse_item(self): # ITEM: '[' RHS ']' | ATOM ['+' | '*'] if self.value == "[": self.gettoken() a, z = self.parse_rhs() self.expect(token.OP, "]") a.addarc(z) return a, z else: a, z = self.parse_atom() value = self.value if value not in ("+", "*"): return a, z self.gettoken() z.addarc(a) if value == "+": return a, z else: return a, a def parse_atom(self): # ATOM: '(' RHS ')' | NAME | STRING if self.value == "(": self.gettoken() a, z = self.parse_rhs() self.expect(token.OP, ")") return a, z elif self.type in (token.NAME, token.STRING): a = NFAState() z = NFAState() a.addarc(z, self.value) self.gettoken() return a, z else: self.raise_error("expected (...) or NAME or STRING, got %s/%s", self.type, self.value) def expect(self, type, value=None): if self.type != type or (value is not None and self.value != value): self.raise_error("expected %s/%s, got %s/%s", type, value, self.type, self.value) value = self.value self.gettoken() return value def gettoken(self): tup = next(self.generator) while tup[0] in (tokenize.COMMENT, tokenize.NL): tup = next(self.generator) self.type, self.value, self.begin, self.end, self.line = tup #print token.tok_name[self.type], repr(self.value) def raise_error(self, msg, *args): if args: try: msg = msg % args except: msg = " ".join([msg] + list(map(str, args))) raise SyntaxError(msg, (self.filename, self.end[0], self.end[1], self.line)) class NFAState(object): def __init__(self): self.arcs = [] # list of (label, NFAState) pairs def addarc(self, next, label=None): assert label is None or isinstance(label, str) assert isinstance(next, NFAState) self.arcs.append((label, next)) class DFAState(object): def __init__(self, nfaset, final): assert isinstance(nfaset, dict) assert isinstance(next(iter(nfaset)), NFAState) assert isinstance(final, NFAState) self.nfaset = nfaset self.isfinal = final in nfaset self.arcs = {} # map from label to DFAState def addarc(self, next, label): assert isinstance(label, str) assert label not in self.arcs assert isinstance(next, DFAState) self.arcs[label] = next def unifystate(self, old, new): for label, next in self.arcs.items(): if next is old: self.arcs[label] = new def __eq__(self, other): # Equality test -- ignore the nfaset instance variable assert isinstance(other, DFAState) if self.isfinal != other.isfinal: return False # Can't just return self.arcs == other.arcs, because that # would invoke this method recursively, with cycles... if len(self.arcs) != len(other.arcs): return False for label, next in self.arcs.items(): if next is not other.arcs.get(label): return False return True __hash__ = None # For Py3 compatibility. def generate_grammar(filename="Grammar.txt"): p = ParserGenerator(filename) return p.make_grammar()