parsers.py 44.1 KB
Newer Older
1
"""parsers.py - parser combinators for for DHParser
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

Copyright 2016  by Eckhart Arnold (arnold@badw.de)
                Bavarian Academy of Sciences an Humanities (badw.de)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
implied.  See the License for the specific language governing
permissions and limitations under the License.
Eckhart Arnold's avatar
Eckhart Arnold committed
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

Module ``parsers.py`` contains a number of classes that together
make up parser combinators for left-recursive grammers. For each
element of the extended Backus-Naur-Form as well as for a regular
expression token a class is defined. The set of classes can be used to
define a parser for (ambiguous) left-recursive grammers.


References and Acknowledgements:

Dominikus Herzberg: Objekt-orientierte Parser-Kombinatoren in Python,
Blog-Post, September, 18th 2008 on denkspuren. gedanken, ideen,
anregungen und links rund um informatik-themen, URL:
http://denkspuren.blogspot.de/2008/09/objekt-orientierte-parser-kombinatoren.html

Dominikus Herzberg: Eine einfache Grammatik für LaTeX, Blog-Post,
September, 18th 2008 on denkspuren. gedanken, ideen, anregungen und
links rund um informatik-themen, URL:
http://denkspuren.blogspot.de/2008/09/eine-einfache-grammatik-fr-latex.html

Dominikus Herzberg: Uniform Syntax, Blog-Post, February, 27th 2007 on
denkspuren. gedanken, ideen, anregungen und links rund um
informatik-themen, URL:
http://denkspuren.blogspot.de/2007/02/uniform-syntax.html

Richard A. Frost, Rahmatullah Hafiz and Paul Callaghan: Parser
Combinators for Ambiguous Left-Recursive Grammars, in: P. Hudak and
D.S. Warren (Eds.): PADL 2008, LNCS 4902, pp. 167–181, Springer-Verlag
Berlin Heidelberg 2008.

Juancarlo Añez: grako, a PEG parser generator in Python,
https://bitbucket.org/apalala/grako
49
50
"""

51

Eckhart Arnold's avatar
Eckhart Arnold committed
52
import abc
53
54
import copy
import os
55
56
from functools import partial

57
58
59
60
try:
    import regex as re
except ImportError:
    import re
Eckhart Arnold's avatar
Eckhart Arnold committed
61
from typing import Any, Callable, Collection, Dict, Iterator, List, Set, Tuple, Union
62

63
from DHParser.toolkit import is_logging, log_dir, logfile_basename, escape_re, sane_parser_name
Eckhart Arnold's avatar
Eckhart Arnold committed
64
65
from DHParser.syntaxtree import WHITESPACE_PTYPE, TOKEN_PTYPE, ZOMBIE_PARSER, ParserBase, \
    Node, TransformationFunc
66
from DHParser.toolkit import load_if_file, error_messages
Eckhart Arnold's avatar
Eckhart Arnold committed
67

68
69
__all__ = ['ScannerFunc',
           'HistoryRecord',
Eckhart Arnold's avatar
Eckhart Arnold committed
70
           'Parser',
71
           'Grammar',
Eckhart Arnold's avatar
Eckhart Arnold committed
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
           'RX_SCANNER_TOKEN',
           'BEGIN_SCANNER_TOKEN',
           'END_SCANNER_TOKEN',
           'make_token',
           'nil_scanner',
           'ScannerToken',
           'RegExp',
           'RE',
           'Token',
           'mixin_comment',
           'UnaryOperator',
           'NaryOperator',
           'Optional',
           'ZeroOrMore',
           'OneOrMore',
           'Sequence',
           'Alternative',
           'FlowOperator',
           'Required',
           'Lookahead',
           'NegativeLookahead',
           'Lookbehind',
           'NegativeLookbehind',
           'Capture',
           'Retrieve',
           'Pop',
           'Forward',
99
           'Compiler',
Eckhart Arnold's avatar
Eckhart Arnold committed
100
           'compile_source']
Eckhart Arnold's avatar
Eckhart Arnold committed
101

102

103
104
105
106
107
108
109
110
111
112
########################################################################
#
# Grammar and parsing infrastructure
#
########################################################################


ScannerFunc = Union[Callable[[str], str], partial]


113
LEFT_RECURSION_DEPTH = 10  # because of pythons recursion depth limit, this
Eckhart Arnold's avatar
Eckhart Arnold committed
114
                           # value ought not to be set too high
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
MAX_DROPOUTS = 25  # stop trying to recover parsing after so many errors


class HistoryRecord:
    """
    Stores debugging information about one completed step in the
    parsing history. 

    A parsing step is "completed" when the last one of a nested
    sequence of parser-calls returns. The call stack including
    the last parser call will be frozen in the ``HistoryRecord``-
    object. In addition a reference to the generated leaf node
    (if any) will be stored and the result status of the last
    parser call, which ist either MATCH, FAIL (i.e. no match)
    or ERROR.
    """
    __slots__ = ('call_stack', 'node', 'remaining')

    MATCH = "MATCH"
    ERROR = "ERROR"
    FAIL = "FAIL"

    def __init__(self, call_stack, node, remaining):
        self.call_stack = call_stack
        self.node = node
        self.remaining = remaining

142
    def err_msg(self) -> str:
143
144
        return self.ERROR + ": " + "; ".join(self.node._errors).replace('\n', '\\')

145
    @property
146
    def stack(self) -> str:
147
148
149
        return "->".join(str(parser) for parser in self.call_stack)

    @property
150
    def status(self) -> str:
151
152
        return self.FAIL if self.node is None else \
            self.err_msg() if self.node._errors else self.MATCH
153
154

    @property
155
    def extent(self) -> Tuple[int, int]:
156
157
158
159
160
        return ((-self.remaining - self.node.len, -self.remaining) if self.node
                else (-self.remaining, None))


def add_parser_guard(parser_func):
161
    def guarded_call(parser: 'Parser', text: str) -> Tuple[Node, str]:
162
163
164
165
166
167
168
169
170
171
172
        try:
            location = len(text)
            # if location has already been visited by the current parser,
            # return saved result
            if location in parser.visited:
                return parser.visited[location]
            # break left recursion at the maximum allowed depth
            if parser.recursion_counter.setdefault(location, 0) > LEFT_RECURSION_DEPTH:
                return None, text

            parser.recursion_counter[location] += 1
Eckhart Arnold's avatar
Eckhart Arnold committed
173
            grammar = parser.grammar    # grammar may be 'None' for unconnected parsers!
174

Eckhart Arnold's avatar
Eckhart Arnold committed
175
            if grammar and grammar.history_tracking:
176
177
178
179
180
181
                grammar.call_stack.append(parser)
                grammar.moving_forward = True

            # run original __call__ method
            node, rest = parser_func(parser, text)

Eckhart Arnold's avatar
Eckhart Arnold committed
182
            if grammar and grammar.history_tracking:
183
184
                # don't track returning parsers except in case an error has occurred
                if grammar.moving_forward or (node and node._errors):
185
186
187
                    grammar.moving_forward = False
                    record = HistoryRecord(grammar.call_stack.copy(), node, len(rest))
                    grammar.history.append(record)
188
                    # print(record.stack, record.status, rest[:20].replace('\n', '|'))
189
190
191
192
193
194
                grammar.call_stack.pop()

            if node is not None:
                # in case of a recursive call saves the result of the first
                # (or left-most) call that matches
                parser.visited[location] = (node, rest)
Eckhart Arnold's avatar
Eckhart Arnold committed
195
196
                if grammar:
                    grammar.last_node = node   # store last node for Lookbehind operator
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
            elif location in parser.visited:
                # if parser did non match but a saved result exits, assume
                # left recursion and use the saved result
                node, rest = parser.visited[location]

            parser.recursion_counter[location] -= 1

        except RecursionError:
            node = Node(None, text[:min(10, max(1, text.find("\n")))] + " ...")
            node.add_error("maximum recursion depth of parser reached; "
                           "potentially due to too many errors!")
            node.error_flag = True
            rest = ''

        return node, rest

    return guarded_call


Eckhart Arnold's avatar
Eckhart Arnold committed
216
class ParserMetaClass(abc.ABCMeta):
217
218
219
220
221
222
223
224
225
226
    def __init__(cls, name, bases, attrs):
        # The following condition is necessary for classes that don't override
        # the __call__() method, because in these cases the non-overridden
        # __call__()-method would be substituted a second time!
        guarded_parser_call = add_parser_guard(cls.__call__)
        if cls.__call__.__code__ != guarded_parser_call.__code__:
            cls.__call__ = guarded_parser_call
        super(ParserMetaClass, cls).__init__(name, bases, attrs)


Eckhart Arnold's avatar
Eckhart Arnold committed
227
class Parser(ParserBase, metaclass=ParserMetaClass):
228
229
    ApplyFunc = Callable[['Parser'], None]

230
231
    def __init__(self, name: str = '') -> None:
        # assert isinstance(name, str), str(name)
Eckhart Arnold's avatar
Eckhart Arnold committed
232
        super(Parser, self).__init__(name)
233
        self._grammar = None  # type: 'Grammar'
234
235
        self.reset()

Eckhart Arnold's avatar
Eckhart Arnold committed
236
    def __deepcopy__(self, memo):
237
238
        return self.__class__(self.name)

239
    def reset(self):
240
241
242
        self.visited = dict()  # type: Dict[int, Tuple[Node, str]]
        self.recursion_counter = dict()  # type: Dict[int, int]
        self.cycle_detection = set()  # type: Set[Callable]
243
        return self
244

245
    def __call__(self, text: str) -> Tuple[Node, str]:
246
247
248
        return None, text  # default behaviour: don't match

    def __str__(self):
249
        return self.name or self.ptype
250

251
252
253
254
255
256
    def __add__(self, other):
        return Sequence(self, other)

    def __or__(self, other):
        return Alternative(self, other)

257
    @property
258
    def grammar(self) -> 'Grammar':
259
260
261
        return self._grammar

    @grammar.setter
262
263
    def grammar(self, grammar: 'Grammar'):
        self._grammar = grammar
264
265
266
267
268
        self._grammar_assigned_notifier()

    def _grammar_assigned_notifier(self):
        pass

269
    def apply(self, func: ApplyFunc):
270
        """Applies function `func(parser)` recursively to this parser and all
Eckhart Arnold's avatar
Eckhart Arnold committed
271
        descendants of the tree of parsers. The same function can never
272
273
274
275
276
277
278
279
280
281
        be applied twice between calls of the ``reset()``-method!
        """
        if func in self.cycle_detection:
            return False
        else:
            self.cycle_detection.add(func)
            func(self)
            return True


282
class Grammar:
283
284
    root__ = None  # type: Union[Parser, None]
    # root__ must be overwritten with the root-parser by grammar subclass
Eckhart Arnold's avatar
Eckhart Arnold committed
285
    parser_initialization__ = "pending"  # type: str
286
287
288
289
290
291

    @classmethod
    def _assign_parser_names(cls):
        """Initializes the `parser.name` fields of those
        Parser objects that are directly assigned to a class field with
        the field's name, e.g.
292
            class Grammar(Grammar):
293
294
295
                ...
                symbol = RE('(?!\\d)\\w+')
        After the call of this method symbol.name == "symbol"
296
297
298
299
300
301
302
303
304
305
        holds. Names assigned via the ``name``-parameter of the
        constructor will not be overwritten. Parser names starting or
        ending with a double underscore like ``root__`` will be
        ignored. See ``toolkit.sane_parser_name()``
        
        Attention: If there exists more than one reference to the same
        parser, only the first one will be chosen for python versions 
        greater or equal 3.6.  For python version <= 3.5 an arbitrarily
        selected reference will be chosen. See PEP 520
        (www.python.org/dev/peps/pep-0520/) for an explanation of why. 
306
307
308
309
310
        """
        if cls.parser_initialization__ == "done":
            return
        cdict = cls.__dict__
        for entry, parser in cdict.items():
311
            if isinstance(parser, Parser) and sane_parser_name(entry):
312
                if not parser.name:
313
                    parser.name = entry
314
                if (isinstance(parser, Forward) and (not parser.parser.name)):
315
316
317
                    parser.parser.name = entry
        cls.parser_initialization__ = "done"

Eckhart Arnold's avatar
Eckhart Arnold committed
318
319
320
    def __init__(self, root: Parser=None) -> None:
        # if not hasattr(self.__class__, 'parser_initialization__'):
        #     self.__class__.parser_initialization__ = "pending"
321
322
323
324
        if not hasattr(self.__class__, 'wspL__'):
            self.wspL__ = ''
        if not hasattr(self.__class__, 'wspR__'):
            self.wspR__ = ''
Eckhart Arnold's avatar
Eckhart Arnold committed
325
        self.all_parsers = set()  # type: Set[Parser]
326
        self.dirty_flag = False
327
        self.history_tracking = False
328
329
        self._reset()
        self._assign_parser_names()
330
        self.root__ = root if root else copy.deepcopy(self.__class__.root__)
331
        if self.wspL__:
Eckhart Arnold's avatar
Eckhart Arnold committed
332
            self.wsp_left_parser__ = Whitespace(self.wspL__)  # type: ParserBase
333
            self.wsp_left_parser__.grammar = self
334
            self.all_parsers.add(self.wsp_left_parser__)  # don't you forget about me...
335
336
337
        else:
            self.wsp_left_parser__ = ZOMBIE_PARSER
        if self.wspR__:
Eckhart Arnold's avatar
Eckhart Arnold committed
338
            self.wsp_right_parser__ = Whitespace(self.wspR__)  # type: ParserBase
339
            self.wsp_right_parser__.grammar = self
340
            self.all_parsers.add(self.wsp_right_parser__)  # don't you forget about me...
341
342
343
344
        else:
            self.wsp_right_parser__ = ZOMBIE_PARSER
        self.root__.apply(self._add_parser)

345
346
347
    def __getitem__(self, key):
        return self.__dict__[key]

348
    def _reset(self):
349
350
351
352
353
354
355
356
357
358
359
360
        # variables stored and recalled by Capture and Retrieve parsers
        self.variables = dict()  # type: Dict[str, List[str]]
        self.document = ""  # type: str
        # previously parsed node, needed by Lookbehind parser
        self.last_node = None  # type: Node
        # support for call stack tracing
        self.call_stack = []  # type: List[Parser]
        # snapshots of call stacks
        self.history = []  # type: List[HistoryRecord]
        # also needed for call stack tracing
        self.moving_forward = True

Eckhart Arnold's avatar
Eckhart Arnold committed
361
    def _add_parser(self, parser: Parser) -> None:
362
        """Adds the copy of the classes parser object to this
363
        particular instance of Grammar.
364
        """
365
366
        if parser.name:
            setattr(self, parser.name, parser)
367
368
369
        self.all_parsers.add(parser)
        parser.grammar = self

Eckhart Arnold's avatar
Eckhart Arnold committed
370
    def __call__(self, document: str, start_parser="root__") -> Node:
371
372
373
374
        """Parses a document with with parser-combinators.

        Args:
            document (str): The source text to be parsed.
375
376
377
            start_parser (str): The name of the parser with which to
                start. This is useful for testing particular parsers
                (i.e. particular parts of the EBNF-Grammar.)
378
379
380
        Returns:
            Node: The root node ot the parse tree.
        """
381
        # assert isinstance(document, str), type(document)
382
383
384
385
386
387
388
389
        if self.root__ is None:
            raise NotImplementedError()
        if self.dirty_flag:
            self._reset()
            for parser in self.all_parsers:
                parser.reset()
        else:
            self.dirty_flag = True
390
        self.history_tracking = is_logging()
391
        self.document = document
Eckhart Arnold's avatar
Eckhart Arnold committed
392
393
        parser = self[start_parser] if isinstance(start_parser, str) else start_parser
        assert parser.grammar == self, "Cannot run parsers from a differen grammar object!"
394
        stitches = []  # type: List[Node]
395
        rest = document
396
397
        if not rest:
            result, ignore = parser(rest)
398
399
400
401
402
403
404
405
406
407
        while rest and len(stitches) < MAX_DROPOUTS:
            result, rest = parser(rest)
            if rest:
                fwd = rest.find("\n") + 1 or len(rest)
                skip, rest = rest[:fwd], rest[fwd:]
                if result is None:
                    error_msg = "Parser did not match! Invalid source file?"
                else:
                    stitches.append(result)
                    error_msg = "Parser stopped before end" + \
408
409
410
                                (("! trying to recover" +
                                  (" but stopping history recording at this point."
                                   if self.history_tracking else "..."))
411
412
413
414
                                 if len(stitches) < MAX_DROPOUTS
                                 else " too often! Terminating parser.")
                stitches.append(Node(None, skip))
                stitches[-1].add_error(error_msg)
415
                if self.history_tracking:
416
417
418
419
420
421
422
                    # some parsers may have matched and left history records with nodes != None.
                    # Because these are not connected to the stiched root node, their pos
                    # properties will not be initialized by setting the root node's pos property
                    # to zero. Therefore, their pos properties need to be initialized here
                    for record in self.history:
                        if record.node and record.node._pos < 0:
                            record.node.pos = 0
423
424
425
                    record = HistoryRecord(self.call_stack.copy(), stitches[-1], len(rest))
                    self.history.append(record)
                    self.history_tracking = False
426
427
428
429
430
431
432
        if stitches:
            if rest:
                stitches.append(Node(None, rest))
            result = Node(None, tuple(stitches))
        result.pos = 0  # calculate all positions
        return result

Eckhart Arnold's avatar
Eckhart Arnold committed
433
    def log_parsing_history(self, log_file_name: str='') -> None:
434
435
436
437
438
439
        """Writes a log of the parsing history of the most recently parsed
        document. 
        """
        def prepare_line(record):
            excerpt = self.document.__getitem__(slice(*record.extent))[:25].replace('\n', '\\n')
            excerpt = "'%s'" % excerpt if len(excerpt) < 25 else "'%s...'" % excerpt
440
            return record.stack, record.status, excerpt
441
442

        def write_log(history, log_name):
Eckhart Arnold's avatar
Eckhart Arnold committed
443
            path = os.path.join(log_dir(), log_name + "_parser.log")
444
445
446
447
448
449
            if history:
                with open(path, "w", encoding="utf-8") as f:
                    f.write("\n".join(history))
            elif os.path.exists(path):
                os.remove(path)

Eckhart Arnold's avatar
Eckhart Arnold committed
450
451
452
453
454
455
456
        if not log_file_name:
            name = self.__class__.__name__
            log_file_name = name[:-7] if name.lower().endswith('grammar') else name
        full_history, match_history, errors_only = [], [], []
        for record in self.history:
            line = ";  ".join(prepare_line(record))
            full_history.append(line)
457
            if record.node and record.node.parser.ptype != WHITESPACE_PTYPE:
Eckhart Arnold's avatar
Eckhart Arnold committed
458
459
460
461
462
463
                match_history.append(line)
                if record.node.errors:
                    errors_only.append(line)
        write_log(full_history, log_file_name + '_full')
        write_log(match_history, log_file_name + '_match')
        write_log(errors_only, log_file_name + '_errors')
464
465


Eckhart Arnold's avatar
Eckhart Arnold committed
466
467
def dsl_error_msg(parser: Parser, error_str: str) -> str:
    """Returns an error message for errors in the parser configuration,
468
469
470
    e.g. errors that result in infinite loops.

    Args:
Eckhart Arnold's avatar
Eckhart Arnold committed
471
        parser (Parser):  The parser where the error was noticed. Note
472
            that this is not necessarily the parser that caused the
Eckhart Arnold's avatar
Eckhart Arnold committed
473
            error but only where the error became aparent.
474
475
476
477
478
479
480
481
482
483
484
485
486
        error_str (str):  A short string describing the error.
    Returns:  
        str: An error message including the call stack if history 
        tacking has been turned in the grammar object.
    """
    msg = ["DSL parser specification error:", error_str, "caught by parser", str(parser)]
    if parser.grammar.history:
        msg.extend(["\nCall stack:", parser.grammar.history[-1].stack])
    else:
        msg.extend(["\nEnable history tracking in Grammar object to display call stack."])
    return " ".join(msg)


487
488
489
490
491
492
493
494
495
496
497
498
########################################################################
#
# Token and Regular Expression parser classes (i.e. leaf classes)
#
########################################################################


RX_SCANNER_TOKEN = re.compile('\w+')
BEGIN_SCANNER_TOKEN = '\x1b'
END_SCANNER_TOKEN = '\x1c'


499
def make_token(token: str, argument: str = '') -> str:
500
501
502
503
504
505
506
507
508
509
510
511
512
    """Turns the ``token`` and ``argument`` into a special token that
    will be caught by the `ScannerToken`-parser.

    This function is a support function that should be used by scanners
    to inject scanner tokens into the source text.
    """
    assert RX_SCANNER_TOKEN.match(token)
    assert argument.find(BEGIN_SCANNER_TOKEN) < 0
    assert argument.find(END_SCANNER_TOKEN) < 0

    return BEGIN_SCANNER_TOKEN + token + argument + END_SCANNER_TOKEN


513
def nil_scanner(text: str) -> str:
Eckhart Arnold's avatar
Eckhart Arnold committed
514
    return text
515
516
517


class ScannerToken(Parser):
518
519
520
521
522
523
524
525
526
527
    """
    Parses tokens that have been inserted by a Scanner.
    
    Scanners can generate Tokens with the ``make_token``-function.
    These tokens start and end with magic characters that can only be
    matched by the ScannerToken Parser. Scanner tokens can be used to
    insert BEGIN - END delimiters at the beginning or ending of an 
    indented block. Otherwise indented block are difficult to handle 
    with parsing expression grammars.
    """
528
529
530

    def __init__(self, scanner_token: str) -> None:
        assert scanner_token and scanner_token.isupper()
531
        assert RX_SCANNER_TOKEN.match(scanner_token)
532
        super(ScannerToken, self).__init__(scanner_token)
533

534
    def __call__(self, text: str) -> Tuple[Node, str]:
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
        if text[0:1] == BEGIN_SCANNER_TOKEN:
            end = text.find(END_SCANNER_TOKEN, 1)
            if end < 0:
                node = Node(self, '').add_error(
                    'END_SCANNER_TOKEN delimiter missing from scanner token. '
                    '(Most likely due to a scanner bug!)')
                return node, text[1:]
            elif end == 0:
                node = Node(self, '').add_error(
                    'Scanner token cannot have zero length. '
                    '(Most likely due to a scanner bug!)')
                return node, text[2:]
            elif text.find(BEGIN_SCANNER_TOKEN, 1, end) >= 0:
                node = Node(self, text[len(self.name) + 1:end])
                node.add_error(
                    'Scanner tokens must not be nested or contain '
                    'BEGIN_SCANNER_TOKEN delimiter as part of their argument. '
                    '(Most likely due to a scanner bug!)')
                return node, text[end:]
            if text[1:len(self.name) + 1] == self.name:
                return Node(self, text[len(self.name) + 1:end]), \
                       text[end + 1:]
        return None, text


class RegExp(Parser):
561
562
    """
    Regular expression parser.
563
564
565
566
567
568
    
    The RegExp-parser parses text that matches a regular expression.
    RegExp can also be considered as the "atomic parser", because all
    other parsers delegate part of the parsing job to other parsers,
    but do not match text directly.
    """
569
570

    def __init__(self, regexp, name: str = '') -> None:
571
        super(RegExp, self).__init__(name)
572
573
574
        self.regexp = re.compile(regexp) if isinstance(regexp, str) else regexp

    def __deepcopy__(self, memo):
Eckhart Arnold's avatar
Eckhart Arnold committed
575
        # `regex` supports deep copies, but not `re`
576
        try:
Eckhart Arnold's avatar
Eckhart Arnold committed
577
            regexp = copy.deepcopy(self.regexp, memo)
578
579
        except TypeError:
            regexp = self.regexp.pattern
580
        return RegExp(regexp, self.name)
581

582
    def __call__(self, text: str) -> Tuple[Node, str]:
583
584
585
586
587
588
        match = text[0:1] != BEGIN_SCANNER_TOKEN and self.regexp.match(text)  # ESC starts a scanner token.
        if match:
            end = match.end()
            return Node(self, text[:end]), text[end:]
        return None, text

589
590
591
    def __str__(self):
        return self.name or self.ptype + ' /%s/' % self.regexp.pattern

592

593
594
class Whitespace(RegExp):
    assert WHITESPACE_PTYPE == ":Whitespace"
595
596


597
598
class RE(Parser):
    """Regular Expressions with optional leading or trailing whitespace.
599
600
601
602
603
604
605
606
607
608
    
    The RE-parser parses pieces of text that match a given regular
    expression. Other than the ``RegExp``-Parser it can also skip 
    "implicit whitespace" before or after the matched text.
    
    The whitespace is in turn defined by a regular expression. It
    should be made sure that this expression also matches the empty
    string, e.g. use r'\s*' or r'[\t ]+', but not r'\s+'. If the
    respective parameters in the constructor are set to ``None`` the
    default whitespace expression from the Grammar object will be used.
609
    """
610
    def __init__(self, regexp, wL=None, wR=None, name=''):
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
        """Constructor for class RE.
                
        Args:
            regexp (str or regex object):  The regular expression to be
                used for parsing. 
            wL (str or regexp):  Left whitespace regular expression, 
                i.e. either ``None``, the empty string or a regular
                expression (e.g. "\s*") that defines whitespace. An 
                empty string means no whitespace will be skipped,
                ``None`` means that the default whitespace will be 
                used.
            wR (str or regexp):  Right whitespace regular expression.
                See above.
            name:  The optional name of the parser.
        """
626
        super(RE, self).__init__(name)
627
628
        self.wL = wL
        self.wR = wR
629
630
        self.wspLeft = Whitespace(wL) if wL else ZOMBIE_PARSER
        self.wspRight = Whitespace(wR) if wR else ZOMBIE_PARSER
631
632
        self.main = RegExp(regexp)

Eckhart Arnold's avatar
Eckhart Arnold committed
633
634
635
636
637
    def __deepcopy__(self, memo={}):
        try:
            regexp = copy.deepcopy(self.main.regexp, memo)
        except TypeError:
            regexp = self.main.regexp.pattern
638
        return self.__class__(regexp, self.wL, self.wR, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
639

640
    def __call__(self, text: str) -> Tuple[Node, str]:
641
642
643
644
645
646
647
648
649
650
651
        # assert self.main.regexp.pattern != "@"
        t = text
        wL, t = self.wspLeft(t)
        main, t = self.main(t)
        if main:
            wR, t = self.wspRight(t)
            result = tuple(nd for nd in (wL, main, wR)
                           if nd and nd.result != '')
            return Node(self, result), t
        return None, text

652
    def __str__(self):
653
        if self.ptype == TOKEN_PTYPE:
654
655
656
            return 'Token "%s"' % self.main.regexp.pattern.replace('\\', '')
        return self.name or ('RE ' + ('~' if self.wL else '')
                             + '/%s/' % self.main.regexp.pattern + ('~' if self.wR else ''))
657
658
659

    def _grammar_assigned_notifier(self):
        if self.grammar:
660
            # use default whitespace parsers if not otherwise specified
661
662
663
664
665
            if self.wL is None:
                self.wspLeft = self.grammar.wsp_left_parser__
            if self.wR is None:
                self.wspRight = self.grammar.wsp_right_parser__

666
    def apply(self, func: Parser.ApplyFunc):
667
668
669
670
671
672
673
674
        if super(RE, self).apply(func):
            if self.wL:
                self.wspLeft.apply(func)
            if self.wR:
                self.wspRight.apply(func)
            self.main.apply(func)


675
676
677
class Token(RE):
    assert TOKEN_PTYPE == ":Token"

678
    def __init__(self, token: str, wL=None, wR=None, name: str = '') -> None:
679
680
681
682
683
        self.token = token
        super(Token, self).__init__(escape_re(token), wL, wR, name)

    def __deepcopy__(self, memo={}):
        return self.__class__(self.token, self.wL, self.wR, self.name)
684
685


686
def mixin_comment(whitespace: str, comment: str) -> str:
687
688
689
690
691
692
693
    """Returns a regular expression that merges comment and whitespace
    regexps. Thus comments cann occur whereever whitespace is allowed
    and will be skipped just as implicit whitespace.
    
    Note, that because this works on the level of regular expressions,
    nesting comments is not possible. It also makes it much harder to
    use directives inside comments (which isn't recommended, anyway).
694
695
696
697
698
699
700
701
702
703
704
705
706
    """
    wspc = '(?:' + whitespace + '(?:' + comment + whitespace + ')*)'
    return wspc


########################################################################
#
# Combinator parser classes (i.e. trunk classes of the parser tree)
#
########################################################################


class UnaryOperator(Parser):
707
    def __init__(self, parser: Parser, name: str = '') -> None:
708
        super(UnaryOperator, self).__init__(name)
709
        # assert isinstance(parser, Parser)
710
        self.parser = parser  # type: Parser
711

Eckhart Arnold's avatar
Eckhart Arnold committed
712
713
    def __deepcopy__(self, memo):
        parser = copy.deepcopy(self.parser, memo)
714
        return self.__class__(parser, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
715

716
    def apply(self, func: Parser.ApplyFunc):
717
718
719
720
721
        if super(UnaryOperator, self).apply(func):
            self.parser.apply(func)


class NaryOperator(Parser):
722
    def __init__(self, *parsers: Parser, name: str = '') -> None:
723
        super(NaryOperator, self).__init__(name)
724
725
        # assert all([isinstance(parser, Parser) for parser in parsers]), str(parsers)
        self.parsers = parsers  # type: Collection  ## [Parser]
726

Eckhart Arnold's avatar
Eckhart Arnold committed
727
728
    def __deepcopy__(self, memo):
        parsers = copy.deepcopy(self.parsers, memo)
729
        return self.__class__(*parsers, name=self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
730

731
    def apply(self, func: Parser.ApplyFunc):
732
733
734
735
736
737
        if super(NaryOperator, self).apply(func):
            for parser in self.parsers:
                parser.apply(func)


class Optional(UnaryOperator):
738
    def __init__(self, parser: Parser, name: str = '') -> None:
739
        super(Optional, self).__init__(parser, name)
740
        # assert isinstance(parser, Parser)
741
742
743
744
        assert not isinstance(parser, Optional), \
            "Nesting options would be redundant: %s(%s)" % \
            (str(name), str(parser.name))
        assert not isinstance(parser, Required), \
745
            "Nesting options with required elements is contradictory: " \
746
747
            "%s(%s)" % (str(name), str(parser.name))

748
    def __call__(self, text: str) -> Tuple[Node, str]:
749
750
751
752
753
754
755
        node, text = self.parser(text)
        if node:
            return Node(self, node), text
        return Node(self, ()), text


class ZeroOrMore(Optional):
756
757
    def __call__(self, text: str) -> Tuple[Node, str]:
        results = ()  # type: Tuple[Node, ...]
758
759
760
        n = len(text) + 1
        while text and len(text) < n:
            n = len(text)
761
762
763
            node, text = self.parser(text)
            if not node:
                break
764
            if len(text) == n:
di68kap's avatar
di68kap committed
765
                node.add_error(dsl_error_msg(self, 'Infinite Loop detected.'))
766
767
768
769
770
            results += (node,)
        return Node(self, results), text


class OneOrMore(UnaryOperator):
771
    def __init__(self, parser: Parser, name: str = '') -> None:
772
        super(OneOrMore, self).__init__(parser, name)
773
774
775
776
        assert not isinstance(parser, Optional), \
            "Use ZeroOrMore instead of nesting OneOrMore and Optional: " \
            "%s(%s)" % (str(name), str(parser.name))

777
778
779
    def __call__(self, text: str) -> Tuple[Node, str]:
        results = ()  # type: Tuple[Node, ...]
        text_ = text  # type: str
780
781
782
        n = len(text) + 1
        while text_ and len(text_) < n:
            n = len(text_)
783
784
785
            node, text_ = self.parser(text_)
            if not node:
                break
786
            if len(text_) == n:
787
                node.add_error(dsl_error_msg(self, 'Infinite Loop detected.'))
788
789
790
791
792
793
794
            results += (node,)
        if results == ():
            return None, text
        return Node(self, results), text_


class Sequence(NaryOperator):
795
    def __init__(self, *parsers: Parser, name: str = '') -> None:
796
        super(Sequence, self).__init__(*parsers, name=name)
797
798
        assert len(self.parsers) >= 1

799
800
801
    def __call__(self, text: str) -> Tuple[Node, str]:
        results = ()  # type: Tuple[Node, ...]
        text_ = text  # type: str
802
803
804
805
806
807
808
809
810
811
812
        for parser in self.parsers:
            node, text_ = parser(text_)
            if not node:
                return node, text
            if node.result:  # Nodes with zero-length result are silently omitted
                results += (node,)
            if node.error_flag:
                break
        assert len(results) <= len(self.parsers)
        return Node(self, results), text_

813
    def __add__(self, other: 'Sequence') -> 'Sequence':
814
815
        return Sequence(*self.parsers, other)

816
    def __radd__(self, other: 'Sequence') -> 'Sequence':
817
818
819
820
821
822
823
824
825
        return Sequence(other, *self.parsers)

        # def __iadd__(self, other):
        #     if isinstance(other, Sequence):
        #         self.parsers = self.parsers + other.parsers
        #     else:
        #         self.parsers = self.parsers + (other,)
        #     return self

826
827

class Alternative(NaryOperator):
828
829
830
831
832
833
834
    """Matches if at least one of several alternatives matches. Returns
    the first match.

    This parser represents the EBNF-operator "|" with the qualification
    that both the symmetry and the ambiguity of the EBNF-or-operator
    are broken by selecting the first match.

Eckhart Arnold's avatar
Eckhart Arnold committed
835
836
837
838
    # the order of the sub-expression matters!
    >>> number = RE('\d+') | RE('\d+') + RE('\.') + RE('\d+')
    >>> str(Grammar(number)('3.1416'))
    '3'
839
840

    # the most selective expression should be put first:
Eckhart Arnold's avatar
Eckhart Arnold committed
841
842
843
    >>> number = RE('\d+') + RE('\.') + RE('\d+') | RE('\d+')
    >>> str(Grammar(number)('3.1416'))
    '3.1416'
844
    """
845
846

    def __init__(self, *parsers: Parser, name: str = '') -> None:
847
        super(Alternative, self).__init__(*parsers, name=name)
848
849
850
        assert len(self.parsers) >= 1
        assert all(not isinstance(p, Optional) for p in self.parsers)

851
    def __call__(self, text: str) -> Tuple[Node, str]:
852
853
854
855
856
857
        for parser in self.parsers:
            node, text_ = parser(text)
            if node:
                return Node(self, node), text_
        return None, text

858
859
860
861
862
863
864
865
866
867
868
869
870
    def __or__(self, other):
        return Alternative(*self.parsers, other)

    def __ror__(self, other):
        return Alternative(other, *self.parsers)

        # def __ior__(self, other):
        #     if isinstance(other, Sequence):
        #         self.parsers = self.parsers + other.parsers
        #     else:
        #         self.parsers = self.parsers + (other,)
        #     return self

871
872
873
874
875
876
877
878
879

########################################################################
#
# Flow control operators
#
########################################################################


class FlowOperator(UnaryOperator):
880
    def __init__(self, parser: Parser, name: str = '') -> None:
881
        super(FlowOperator, self).__init__(parser, name)
882
883
884


class Required(FlowOperator):
885
    # Add constructor that checks for logical errors, like `Required(Optional(...))` constructs ?
886
    def __call__(self, text: str) -> Tuple[Node, str]:
887
888
889
890
891
892
893
894
895
896
897
898
899
        node, text_ = self.parser(text)
        if not node:
            m = re.search(r'\s(\S)', text)
            i = max(1, m.regs[1][0]) if m else 1
            node = Node(self, text[:i])
            text_ = text[i:]
            # assert False, "*"+text[:i]+"*"
            node.add_error('%s expected; "%s..." found!' %
                           (str(self.parser), text[:10]))
        return node, text_


class Lookahead(FlowOperator):
900
    def __init__(self, parser: Parser, name: str = '') -> None:
901
        super(Lookahead, self).__init__(parser, name)
902

903
    def __call__(self, text: str) -> Tuple[Node, str]:
904
905
906
907
908
909
        node, text_ = self.parser(text)
        if self.sign(node is not None):
            return Node(self, ''), text
        else:
            return None, text

910
    def sign(self, bool_value) -> bool:
911
912
913
914
        return bool_value


class NegativeLookahead(Lookahead):
915
    def sign(self, bool_value) -> bool:
916
917
918
        return not bool_value


919
def iter_right_branch(node) -> Iterator[Node]:
920
921
922
923
924
925
926
927
928
929
930
931
    """Iterates over the right branch of `node` starting with node itself.
    Iteration is stopped if either there are no child nodes any more or
    if the parser of a node is a Lookahead parser. (Reason is: Since
    lookahead nodes do not advance the parser, it does not make sense
    to look back to them.)
    """
    while node and not isinstance(node.parser, Lookahead):  # the second condition should not be necessary
        yield node  # for well-formed EBNF code
        node = node.children[-1] if node.children else None


class Lookbehind(FlowOperator):
932
    def __init__(self, parser: Parser, name: str = '') -> None:
933
        super(Lookbehind, self).__init__(parser, name)
934
935
        print("WARNING: Lookbehind Operator is experimental!")

936
    def __call__(self, text: str) -> Tuple[Node, str]:
937
938
939
940
941
942
943
944
        if isinstance(self.grammar.last_node, Lookahead):
            return Node(self, '').add_error('Lookbehind right after Lookahead '
                                            'does not make sense!'), text
        if self.sign(self.condition()):
            return Node(self, ''), text
        else:
            return None, text

945
    def sign(self, bool_value) -> bool:
946
947
948
949
950
951
952
953
954
955
956
957
958
959
        return bool_value

    def condition(self):
        node = None
        for node in iter_right_branch(self.grammar.last_node):
            if node.parser.name == self.parser.name:
                return True
        if node and isinstance(self.parser, RegExp) and \
                self.parser.regexp.match(str(node)):  # Is there really a use case for this?
            return True
        return False


class NegativeLookbehind(Lookbehind):
960
    def sign(self, bool_value) -> bool:
961
962
963
964
965
966
967
968
969
970
971
        return not bool_value


########################################################################
#
# Capture and Retrieve operators (for passing variables in the parser)
#
########################################################################


class Capture(UnaryOperator):
972
    def __init__(self, parser: Parser, name: str = '') -> None:
973
        super(Capture, self).__init__(parser, name)
974

975
    def __call__(self, text: str) -> Tuple[Node, str]:
976
977
978
979
        node, text = self.parser(text)
        if node:
            stack = self.grammar.variables.setdefault(self.name, [])
            stack.append(str(node))
980
981
982
            return Node(self, node), text
        else:
            return None, text
983
984


985
986
987
988
989
990
991
992
993
994
995
996
997
def nop_filter(stack):
    return stack[-1]


def counterpart_filter(stack):
    value = stack[-1]
    return value.replace("(", ")").replace("[", "]").replace("{", "}").replace(">", "<")


def accumulating_filter(stack):
    return "".join(stack)


998
999
1000
RetrFilter = Callable[[List[str]], str]


1001
class Retrieve(Parser):
1002
    def __init__(self, symbol: Parser, retrieve_filter: RetrFilter = None, name: str = '') -> None:
1003
1004
        if not name:
            name = symbol.name
1005
        super(Retrieve, self).__init__(name)
1006
        self.symbol = symbol
1007
        self.retrieve_filter = retrieve_filter if retrieve_filter else nop_filter
1008

Eckhart Arnold's avatar
Eckhart Arnold committed
1009
    def __deepcopy__(self, memo):
1010
        return self.__class__(self.symbol, self.retrieve_filter, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
1011

1012
    def __call__(self, text: str) -> Tuple[Node, str]:
1013
1014
1015
1016
1017
1018
1019
        try:
            stack = self.grammar.variables[self.symbol.name]
            value = self.retrieve_filter(stack)
            self.pick_value(stack)
        except (KeyError, IndexError):
            return Node(self, '').add_error(dsl_error_msg(self,
                "%s undefined or exhausted" % self.symbol.name)), text
1020
1021
1022
1023
1024
        if text.startswith(value):
            return Node(self, value), text[len(value):]
        else:
            return None, text

1025
    def pick_value(self, stack: List[str]) -> str:
1026
1027
1028
1029
        return stack[-1]


class Pop(Retrieve):
1030
    def pick_value(self, stack: List[str]) -> str:
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
        return stack.pop()


########################################################################
#
# Forward class (for recursive symbols)
#
########################################################################


class Forward(Parser):
    def __init__(self):
        Parser.__init__(self)
        self.parser = None
1045
        self.cycle_reached = False
1046

Eckhart Arnold's avatar
Eckhart Arnold committed
1047
1048
1049
1050
1051
1052
1053
    def __deepcopy__(self, memo):
        duplicate = self.__class__()
        memo[id(self)] = duplicate
        parser = copy.deepcopy(self.parser, memo)
        duplicate.set(parser)
        return duplicate

1054
    def __call__(self, text: str) -> Tuple[Node, str]:
1055
1056
        return self.parser(text)

1057
1058
1059
1060
1061
1062
1063
1064
    def __str__(self):
        if self.cycle_reached:
            return "..."
        else:
            self.cycle_reached = True
            s = str(self.parser)
            self.cycle_reached = False
            return s
1065

1066
1067
    def set(self, parser: Parser):
        # assert isinstance(parser, Parser)
1068
        self.name = parser.name  # redundant, see Grammar-constructor
1069
1070
        self.parser = parser

1071
    def apply(self, func: Parser.ApplyFunc):
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
        if super(Forward, self).apply(func):
            assert not self.visited
            self.parser.apply(func)


#######################################################################
#
# Syntax driven compilation support
#
#######################################################################


1084
class Compiler:
Eckhart Arnold's avatar
Eckhart Arnold committed
1085
    def __init__(self, grammar_name="", grammar_source=""):
1086
        self.dirty_flag = False
Eckhart Arnold's avatar
Eckhart Arnold committed
1087
        self.set_grammar_name(grammar_name, grammar_source)
1088
1089
1090
1091

    def _reset(self):
        pass

1092
    def __call__(self, node: Node) -> Any:
1093
        """Compiles the abstract syntax tree with the root ``node``.
1094
        
Eckhart Arnold's avatar
Eckhart Arnold committed
1095
        It's called `compile_ast`` to avoid confusion with the 
1096
1097
        ``_compile`` that is called from within the local node 
        compiler methods.
1098
1099
1100
1101
1102
1103
1104
        """
        if self.dirty_flag:
            self._reset()
        else:
            self.dirty_flag = True
        return self._compile(node)

Eckhart Arnold's avatar
Eckhart Arnold committed
1105
1106
1107
1108
1109
1110
1111
    def set_grammar_name(self, grammar_name, grammar_source):
        assert grammar_name == "" or re.match('\w+\Z', grammar_name)
        if not grammar_name and re.fullmatch(r'[\w/:\\]+', grammar_source):
            grammar_name = os.path.splitext(os.path.basename(grammar_source))[0]
        self.grammar_name = grammar_name
        self.grammar_source = load_if_file(grammar_source)

1112
    @staticmethod
1113
    def derive_method_name(node_name: str) -> str:
1114
        """Returns the method name for ``node_name``, e.g.
1115
        >>> Compiler.method_name('expression')
1116
1117
1118
1119
        'on_expression'
        """
        return 'on_' + node_name

1120
    def _compile(self, node: Node) -> Any:
1121
1122
1123
1124
1125
        """Calls the compilation method for the given node and returns
         the result of the compilation.
        
        The method's name is dreived from either the node's parser 
        name or, if the parser is anonymous, the node's parser's class
1126
        name by adding the prefix 'on_'.
1127
1128
1129
1130
1131
        
        Note that ``_compile`` does not call any compilation functions
        for the parsers of the sub nodes by itself. Rather, this should
        be done within the compilation methods.
        """
1132
        elem = node.parser.name or node.parser.ptype[1:]
1133
        if not sane_parser_name(elem):
1134
            node.add_error("Reserved name '%s' not allowed as parser "
1135
                           "name! " % elem + "(Any name starting with "
1136
                           "'_' or '__' or ending with '__' is reserved.)")
1137
1138
            return None
        else:
1139
            compiler = self.__getattribute__(self.derive_method_name(elem))
1140
1141
            result = compiler(node)
            for child in node.children:
1142
                node.error_flag = node.error_flag or child.error_flag
1143
            return result
1144
1145