1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
|
from __future__ import annotations
from abc import abstractmethod
from typing import (
AbstractSet,
Any,
Dict,
Iterable,
Iterator,
List,
Optional,
Set,
Tuple,
TYPE_CHECKING,
Union,
)
if TYPE_CHECKING:
from pegen.parser_generator import ParserGenerator
class GrammarError(Exception):
pass
class GrammarVisitor:
def visit(self, node: Any, *args: Any, **kwargs: Any) -> Any:
"""Visit a node."""
method = "visit_" + node.__class__.__name__
visitor = getattr(self, method, self.generic_visit)
return visitor(node, *args, **kwargs)
def generic_visit(self, node: Iterable[Any], *args: Any, **kwargs: Any) -> None:
"""Called if no explicit visitor function exists for a node."""
for value in node:
if isinstance(value, list):
for item in value:
self.visit(item, *args, **kwargs)
else:
self.visit(value, *args, **kwargs)
class Grammar:
def __init__(self, rules: Iterable[Rule], metas: Iterable[Tuple[str, Optional[str]]]):
self.rules = {rule.name: rule for rule in rules}
self.metas = dict(metas)
def __str__(self) -> str:
return "\n".join(str(rule) for name, rule in self.rules.items())
def __repr__(self) -> str:
lines = ["Grammar("]
lines.append(" [")
for rule in self.rules.values():
lines.append(f" {repr(rule)},")
lines.append(" ],")
lines.append(" {repr(list(self.metas.items()))}")
lines.append(")")
return "\n".join(lines)
def __iter__(self) -> Iterator[Rule]:
yield from self.rules.values()
# Global flag whether we want actions in __str__() -- default off.
SIMPLE_STR = True
class Rule:
def __init__(self, name: str, type: Optional[str], rhs: Rhs, memo: Optional[object] = None):
self.name = name
self.type = type
self.rhs = rhs
self.memo = bool(memo)
self.visited = False
self.nullable = False
self.left_recursive = False
self.leader = False
def is_loop(self) -> bool:
return self.name.startswith("_loop")
def is_gather(self) -> bool:
return self.name.startswith("_gather")
def __str__(self) -> str:
if SIMPLE_STR or self.type is None:
res = f"{self.name}: {self.rhs}"
else:
res = f"{self.name}[{self.type}]: {self.rhs}"
if len(res) < 88:
return res
lines = [res.split(":")[0] + ":"]
lines += [f" | {alt}" for alt in self.rhs.alts]
return "\n".join(lines)
def __repr__(self) -> str:
return f"Rule({self.name!r}, {self.type!r}, {self.rhs!r})"
def __iter__(self) -> Iterator[Rhs]:
yield self.rhs
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
if self.visited:
# A left-recursive rule is considered non-nullable.
return False
self.visited = True
self.nullable = self.rhs.nullable_visit(rules)
return self.nullable
def initial_names(self) -> AbstractSet[str]:
return self.rhs.initial_names()
def flatten(self) -> Rhs:
# If it's a single parenthesized group, flatten it.
rhs = self.rhs
if (
not self.is_loop()
and len(rhs.alts) == 1
and len(rhs.alts[0].items) == 1
and isinstance(rhs.alts[0].items[0].item, Group)
):
rhs = rhs.alts[0].items[0].item.rhs
return rhs
def collect_todo(self, gen: ParserGenerator) -> None:
rhs = self.flatten()
rhs.collect_todo(gen)
class Leaf:
def __init__(self, value: str):
self.value = value
def __str__(self) -> str:
return self.value
def __iter__(self) -> Iterable[str]:
if False:
yield
@abstractmethod
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
raise NotImplementedError
@abstractmethod
def initial_names(self) -> AbstractSet[str]:
raise NotImplementedError
class NameLeaf(Leaf):
"""The value is the name."""
def __str__(self) -> str:
if self.value == "ENDMARKER":
return "$"
return super().__str__()
def __repr__(self) -> str:
return f"NameLeaf({self.value!r})"
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
if self.value in rules:
return rules[self.value].nullable_visit(rules)
# Token or unknown; never empty.
return False
def initial_names(self) -> AbstractSet[str]:
return {self.value}
class StringLeaf(Leaf):
"""The value is a string literal, including quotes."""
def __repr__(self) -> str:
return f"StringLeaf({self.value!r})"
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
# The string token '' is considered empty.
return not self.value
def initial_names(self) -> AbstractSet[str]:
return set()
class Rhs:
def __init__(self, alts: List[Alt]):
self.alts = alts
self.memo: Optional[Tuple[Optional[str], str]] = None
def __str__(self) -> str:
return " | ".join(str(alt) for alt in self.alts)
def __repr__(self) -> str:
return f"Rhs({self.alts!r})"
def __iter__(self) -> Iterator[List[Alt]]:
yield self.alts
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
for alt in self.alts:
if alt.nullable_visit(rules):
return True
return False
def initial_names(self) -> AbstractSet[str]:
names: Set[str] = set()
for alt in self.alts:
names |= alt.initial_names()
return names
def collect_todo(self, gen: ParserGenerator) -> None:
for alt in self.alts:
alt.collect_todo(gen)
class Alt:
def __init__(self, items: List[NamedItem], *, icut: int = -1, action: Optional[str] = None):
self.items = items
self.icut = icut
self.action = action
def __str__(self) -> str:
core = " ".join(str(item) for item in self.items)
if not SIMPLE_STR and self.action:
return f"{core} {{ {self.action} }}"
else:
return core
def __repr__(self) -> str:
args = [repr(self.items)]
if self.icut >= 0:
args.append(f"icut={self.icut}")
if self.action:
args.append(f"action={self.action!r}")
return f"Alt({', '.join(args)})"
def __iter__(self) -> Iterator[List[NamedItem]]:
yield self.items
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
for item in self.items:
if not item.nullable_visit(rules):
return False
return True
def initial_names(self) -> AbstractSet[str]:
names: Set[str] = set()
for item in self.items:
names |= item.initial_names()
if not item.nullable:
break
return names
def collect_todo(self, gen: ParserGenerator) -> None:
for item in self.items:
item.collect_todo(gen)
class NamedItem:
def __init__(self, name: Optional[str], item: Item, type: Optional[str] = None):
self.name = name
self.item = item
self.type = type
self.nullable = False
def __str__(self) -> str:
if not SIMPLE_STR and self.name:
return f"{self.name}={self.item}"
else:
return str(self.item)
def __repr__(self) -> str:
return f"NamedItem({self.name!r}, {self.item!r})"
def __iter__(self) -> Iterator[Item]:
yield self.item
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
self.nullable = self.item.nullable_visit(rules)
return self.nullable
def initial_names(self) -> AbstractSet[str]:
return self.item.initial_names()
def collect_todo(self, gen: ParserGenerator) -> None:
gen.callmakervisitor.visit(self.item)
class Forced:
def __init__(self, node: Plain):
self.node = node
def __str__(self) -> str:
return f"&&{self.node}"
def __iter__(self) -> Iterator[Plain]:
yield self.node
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return True
def initial_names(self) -> AbstractSet[str]:
return set()
class Lookahead:
def __init__(self, node: Plain, sign: str):
self.node = node
self.sign = sign
def __str__(self) -> str:
return f"{self.sign}{self.node}"
def __iter__(self) -> Iterator[Plain]:
yield self.node
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return True
def initial_names(self) -> AbstractSet[str]:
return set()
class PositiveLookahead(Lookahead):
def __init__(self, node: Plain):
super().__init__(node, "&")
def __repr__(self) -> str:
return f"PositiveLookahead({self.node!r})"
class NegativeLookahead(Lookahead):
def __init__(self, node: Plain):
super().__init__(node, "!")
def __repr__(self) -> str:
return f"NegativeLookahead({self.node!r})"
class Opt:
def __init__(self, node: Item):
self.node = node
def __str__(self) -> str:
s = str(self.node)
# TODO: Decide whether to use [X] or X? based on type of X
if " " in s:
return f"[{s}]"
else:
return f"{s}?"
def __repr__(self) -> str:
return f"Opt({self.node!r})"
def __iter__(self) -> Iterator[Item]:
yield self.node
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return True
def initial_names(self) -> AbstractSet[str]:
return self.node.initial_names()
class Repeat:
"""Shared base class for x* and x+."""
def __init__(self, node: Plain):
self.node = node
self.memo: Optional[Tuple[Optional[str], str]] = None
@abstractmethod
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
raise NotImplementedError
def __iter__(self) -> Iterator[Plain]:
yield self.node
def initial_names(self) -> AbstractSet[str]:
return self.node.initial_names()
class Repeat0(Repeat):
def __str__(self) -> str:
s = str(self.node)
# TODO: Decide whether to use (X)* or X* based on type of X
if " " in s:
return f"({s})*"
else:
return f"{s}*"
def __repr__(self) -> str:
return f"Repeat0({self.node!r})"
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return True
class Repeat1(Repeat):
def __str__(self) -> str:
s = str(self.node)
# TODO: Decide whether to use (X)+ or X+ based on type of X
if " " in s:
return f"({s})+"
else:
return f"{s}+"
def __repr__(self) -> str:
return f"Repeat1({self.node!r})"
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return False
class Gather(Repeat):
def __init__(self, separator: Plain, node: Plain):
self.separator = separator
self.node = node
def __str__(self) -> str:
return f"{self.separator!s}.{self.node!s}+"
def __repr__(self) -> str:
return f"Gather({self.separator!r}, {self.node!r})"
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return False
class Group:
def __init__(self, rhs: Rhs):
self.rhs = rhs
def __str__(self) -> str:
return f"({self.rhs})"
def __repr__(self) -> str:
return f"Group({self.rhs!r})"
def __iter__(self) -> Iterator[Rhs]:
yield self.rhs
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return self.rhs.nullable_visit(rules)
def initial_names(self) -> AbstractSet[str]:
return self.rhs.initial_names()
class Cut:
def __init__(self) -> None:
pass
def __repr__(self) -> str:
return f"Cut()"
def __str__(self) -> str:
return f"~"
def __iter__(self) -> Iterator[Tuple[str, str]]:
if False:
yield
def __eq__(self, other: object) -> bool:
if not isinstance(other, Cut):
return NotImplemented
return True
def nullable_visit(self, rules: Dict[str, Rule]) -> bool:
return True
def initial_names(self) -> AbstractSet[str]:
return set()
Plain = Union[Leaf, Group]
Item = Union[Plain, Opt, Repeat, Forced, Lookahead, Rhs, Cut]
RuleName = Tuple[str, str]
MetaTuple = Tuple[str, Optional[str]]
MetaList = List[MetaTuple]
RuleList = List[Rule]
NamedItemList = List[NamedItem]
LookaheadOrCut = Union[Lookahead, Cut]
|