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[etc/vim.git] / blib2to3 / pgen2 / pgen.py
1 # Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
2 # Licensed to PSF under a Contributor Agreement.
3
4 # Pgen imports
5 from . import grammar, token, tokenize
6
7 class PgenGrammar(grammar.Grammar):
8     pass
9
10 class ParserGenerator(object):
11
12     def __init__(self, filename, stream=None):
13         close_stream = None
14         if stream is None:
15             stream = open(filename)
16             close_stream = stream.close
17         self.filename = filename
18         self.stream = stream
19         self.generator = tokenize.generate_tokens(stream.readline)
20         self.gettoken() # Initialize lookahead
21         self.dfas, self.startsymbol = self.parse()
22         if close_stream is not None:
23             close_stream()
24         self.first = {} # map from symbol name to set of tokens
25         self.addfirstsets()
26
27     def make_grammar(self):
28         c = PgenGrammar()
29         names = list(self.dfas.keys())
30         names.sort()
31         names.remove(self.startsymbol)
32         names.insert(0, self.startsymbol)
33         for name in names:
34             i = 256 + len(c.symbol2number)
35             c.symbol2number[name] = i
36             c.number2symbol[i] = name
37         for name in names:
38             dfa = self.dfas[name]
39             states = []
40             for state in dfa:
41                 arcs = []
42                 for label, next in sorted(state.arcs.items()):
43                     arcs.append((self.make_label(c, label), dfa.index(next)))
44                 if state.isfinal:
45                     arcs.append((0, dfa.index(state)))
46                 states.append(arcs)
47             c.states.append(states)
48             c.dfas[c.symbol2number[name]] = (states, self.make_first(c, name))
49         c.start = c.symbol2number[self.startsymbol]
50         return c
51
52     def make_first(self, c, name):
53         rawfirst = self.first[name]
54         first = {}
55         for label in sorted(rawfirst):
56             ilabel = self.make_label(c, label)
57             ##assert ilabel not in first # XXX failed on <> ... !=
58             first[ilabel] = 1
59         return first
60
61     def make_label(self, c, label):
62         # XXX Maybe this should be a method on a subclass of converter?
63         ilabel = len(c.labels)
64         if label[0].isalpha():
65             # Either a symbol name or a named token
66             if label in c.symbol2number:
67                 # A symbol name (a non-terminal)
68                 if label in c.symbol2label:
69                     return c.symbol2label[label]
70                 else:
71                     c.labels.append((c.symbol2number[label], None))
72                     c.symbol2label[label] = ilabel
73                     return ilabel
74             else:
75                 # A named token (NAME, NUMBER, STRING)
76                 itoken = getattr(token, label, None)
77                 assert isinstance(itoken, int), label
78                 assert itoken in token.tok_name, label
79                 if itoken in c.tokens:
80                     return c.tokens[itoken]
81                 else:
82                     c.labels.append((itoken, None))
83                     c.tokens[itoken] = ilabel
84                     return ilabel
85         else:
86             # Either a keyword or an operator
87             assert label[0] in ('"', "'"), label
88             value = eval(label)
89             if value[0].isalpha():
90                 # A keyword
91                 if value in c.keywords:
92                     return c.keywords[value]
93                 else:
94                     c.labels.append((token.NAME, value))
95                     c.keywords[value] = ilabel
96                     return ilabel
97             else:
98                 # An operator (any non-numeric token)
99                 itoken = grammar.opmap[value] # Fails if unknown token
100                 if itoken in c.tokens:
101                     return c.tokens[itoken]
102                 else:
103                     c.labels.append((itoken, None))
104                     c.tokens[itoken] = ilabel
105                     return ilabel
106
107     def addfirstsets(self):
108         names = list(self.dfas.keys())
109         names.sort()
110         for name in names:
111             if name not in self.first:
112                 self.calcfirst(name)
113             #print name, self.first[name].keys()
114
115     def calcfirst(self, name):
116         dfa = self.dfas[name]
117         self.first[name] = None # dummy to detect left recursion
118         state = dfa[0]
119         totalset = {}
120         overlapcheck = {}
121         for label, next in state.arcs.items():
122             if label in self.dfas:
123                 if label in self.first:
124                     fset = self.first[label]
125                     if fset is None:
126                         raise ValueError("recursion for rule %r" % name)
127                 else:
128                     self.calcfirst(label)
129                     fset = self.first[label]
130                 totalset.update(fset)
131                 overlapcheck[label] = fset
132             else:
133                 totalset[label] = 1
134                 overlapcheck[label] = {label: 1}
135         inverse = {}
136         for label, itsfirst in overlapcheck.items():
137             for symbol in itsfirst:
138                 if symbol in inverse:
139                     raise ValueError("rule %s is ambiguous; %s is in the"
140                                      " first sets of %s as well as %s" %
141                                      (name, symbol, label, inverse[symbol]))
142                 inverse[symbol] = label
143         self.first[name] = totalset
144
145     def parse(self):
146         dfas = {}
147         startsymbol = None
148         # MSTART: (NEWLINE | RULE)* ENDMARKER
149         while self.type != token.ENDMARKER:
150             while self.type == token.NEWLINE:
151                 self.gettoken()
152             # RULE: NAME ':' RHS NEWLINE
153             name = self.expect(token.NAME)
154             self.expect(token.OP, ":")
155             a, z = self.parse_rhs()
156             self.expect(token.NEWLINE)
157             #self.dump_nfa(name, a, z)
158             dfa = self.make_dfa(a, z)
159             #self.dump_dfa(name, dfa)
160             oldlen = len(dfa)
161             self.simplify_dfa(dfa)
162             newlen = len(dfa)
163             dfas[name] = dfa
164             #print name, oldlen, newlen
165             if startsymbol is None:
166                 startsymbol = name
167         return dfas, startsymbol
168
169     def make_dfa(self, start, finish):
170         # To turn an NFA into a DFA, we define the states of the DFA
171         # to correspond to *sets* of states of the NFA.  Then do some
172         # state reduction.  Let's represent sets as dicts with 1 for
173         # values.
174         assert isinstance(start, NFAState)
175         assert isinstance(finish, NFAState)
176         def closure(state):
177             base = {}
178             addclosure(state, base)
179             return base
180         def addclosure(state, base):
181             assert isinstance(state, NFAState)
182             if state in base:
183                 return
184             base[state] = 1
185             for label, next in state.arcs:
186                 if label is None:
187                     addclosure(next, base)
188         states = [DFAState(closure(start), finish)]
189         for state in states: # NB states grows while we're iterating
190             arcs = {}
191             for nfastate in state.nfaset:
192                 for label, next in nfastate.arcs:
193                     if label is not None:
194                         addclosure(next, arcs.setdefault(label, {}))
195             for label, nfaset in sorted(arcs.items()):
196                 for st in states:
197                     if st.nfaset == nfaset:
198                         break
199                 else:
200                     st = DFAState(nfaset, finish)
201                     states.append(st)
202                 state.addarc(st, label)
203         return states # List of DFAState instances; first one is start
204
205     def dump_nfa(self, name, start, finish):
206         print("Dump of NFA for", name)
207         todo = [start]
208         for i, state in enumerate(todo):
209             print("  State", i, state is finish and "(final)" or "")
210             for label, next in state.arcs:
211                 if next in todo:
212                     j = todo.index(next)
213                 else:
214                     j = len(todo)
215                     todo.append(next)
216                 if label is None:
217                     print("    -> %d" % j)
218                 else:
219                     print("    %s -> %d" % (label, j))
220
221     def dump_dfa(self, name, dfa):
222         print("Dump of DFA for", name)
223         for i, state in enumerate(dfa):
224             print("  State", i, state.isfinal and "(final)" or "")
225             for label, next in sorted(state.arcs.items()):
226                 print("    %s -> %d" % (label, dfa.index(next)))
227
228     def simplify_dfa(self, dfa):
229         # This is not theoretically optimal, but works well enough.
230         # Algorithm: repeatedly look for two states that have the same
231         # set of arcs (same labels pointing to the same nodes) and
232         # unify them, until things stop changing.
233
234         # dfa is a list of DFAState instances
235         changes = True
236         while changes:
237             changes = False
238             for i, state_i in enumerate(dfa):
239                 for j in range(i+1, len(dfa)):
240                     state_j = dfa[j]
241                     if state_i == state_j:
242                         #print "  unify", i, j
243                         del dfa[j]
244                         for state in dfa:
245                             state.unifystate(state_j, state_i)
246                         changes = True
247                         break
248
249     def parse_rhs(self):
250         # RHS: ALT ('|' ALT)*
251         a, z = self.parse_alt()
252         if self.value != "|":
253             return a, z
254         else:
255             aa = NFAState()
256             zz = NFAState()
257             aa.addarc(a)
258             z.addarc(zz)
259             while self.value == "|":
260                 self.gettoken()
261                 a, z = self.parse_alt()
262                 aa.addarc(a)
263                 z.addarc(zz)
264             return aa, zz
265
266     def parse_alt(self):
267         # ALT: ITEM+
268         a, b = self.parse_item()
269         while (self.value in ("(", "[") or
270                self.type in (token.NAME, token.STRING)):
271             c, d = self.parse_item()
272             b.addarc(c)
273             b = d
274         return a, b
275
276     def parse_item(self):
277         # ITEM: '[' RHS ']' | ATOM ['+' | '*']
278         if self.value == "[":
279             self.gettoken()
280             a, z = self.parse_rhs()
281             self.expect(token.OP, "]")
282             a.addarc(z)
283             return a, z
284         else:
285             a, z = self.parse_atom()
286             value = self.value
287             if value not in ("+", "*"):
288                 return a, z
289             self.gettoken()
290             z.addarc(a)
291             if value == "+":
292                 return a, z
293             else:
294                 return a, a
295
296     def parse_atom(self):
297         # ATOM: '(' RHS ')' | NAME | STRING
298         if self.value == "(":
299             self.gettoken()
300             a, z = self.parse_rhs()
301             self.expect(token.OP, ")")
302             return a, z
303         elif self.type in (token.NAME, token.STRING):
304             a = NFAState()
305             z = NFAState()
306             a.addarc(z, self.value)
307             self.gettoken()
308             return a, z
309         else:
310             self.raise_error("expected (...) or NAME or STRING, got %s/%s",
311                              self.type, self.value)
312
313     def expect(self, type, value=None):
314         if self.type != type or (value is not None and self.value != value):
315             self.raise_error("expected %s/%s, got %s/%s",
316                              type, value, self.type, self.value)
317         value = self.value
318         self.gettoken()
319         return value
320
321     def gettoken(self):
322         tup = next(self.generator)
323         while tup[0] in (tokenize.COMMENT, tokenize.NL):
324             tup = next(self.generator)
325         self.type, self.value, self.begin, self.end, self.line = tup
326         #print token.tok_name[self.type], repr(self.value)
327
328     def raise_error(self, msg, *args):
329         if args:
330             try:
331                 msg = msg % args
332             except:
333                 msg = " ".join([msg] + list(map(str, args)))
334         raise SyntaxError(msg, (self.filename, self.end[0],
335                                 self.end[1], self.line))
336
337 class NFAState(object):
338
339     def __init__(self):
340         self.arcs = [] # list of (label, NFAState) pairs
341
342     def addarc(self, next, label=None):
343         assert label is None or isinstance(label, str)
344         assert isinstance(next, NFAState)
345         self.arcs.append((label, next))
346
347 class DFAState(object):
348
349     def __init__(self, nfaset, final):
350         assert isinstance(nfaset, dict)
351         assert isinstance(next(iter(nfaset)), NFAState)
352         assert isinstance(final, NFAState)
353         self.nfaset = nfaset
354         self.isfinal = final in nfaset
355         self.arcs = {} # map from label to DFAState
356
357     def addarc(self, next, label):
358         assert isinstance(label, str)
359         assert label not in self.arcs
360         assert isinstance(next, DFAState)
361         self.arcs[label] = next
362
363     def unifystate(self, old, new):
364         for label, next in self.arcs.items():
365             if next is old:
366                 self.arcs[label] = new
367
368     def __eq__(self, other):
369         # Equality test -- ignore the nfaset instance variable
370         assert isinstance(other, DFAState)
371         if self.isfinal != other.isfinal:
372             return False
373         # Can't just return self.arcs == other.arcs, because that
374         # would invoke this method recursively, with cycles...
375         if len(self.arcs) != len(other.arcs):
376             return False
377         for label, next in self.arcs.items():
378             if next is not other.arcs.get(label):
379                 return False
380         return True
381
382     __hash__ = None # For Py3 compatibility.
383
384 def generate_grammar(filename="Grammar.txt"):
385     p = ParserGenerator(filename)
386     return p.make_grammar()