parsers.py 42.5 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

52
import copy
53
from functools import partial
54
55
56
57
58
import os
try:
    import regex as re
except ImportError:
    import re
59
from typing import Any, Callable, Dict, Iterator, List, Set, Tuple, Union
60

61
62
63
from DHParser.toolkit import is_logging, log_dir, logfile_basename, escape_re, sane_parser_name
from DHParser.syntaxtree import WHITESPACE_PTYPE, TOKEN_PTYPE, ZOMBIE_PARSER, Node, \
    TransformerFunc
64
from DHParser.toolkit import load_if_file, error_messages
Eckhart Arnold's avatar
Eckhart Arnold committed
65

66
67
__all__ = ['ScannerFunc',
           'HistoryRecord',
Eckhart Arnold's avatar
Eckhart Arnold committed
68
           'Parser',
69
           'Grammar',
Eckhart Arnold's avatar
Eckhart Arnold committed
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
           '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',
97
           'Compiler',
Eckhart Arnold's avatar
Eckhart Arnold committed
98
           'compile_source']
Eckhart Arnold's avatar
Eckhart Arnold committed
99

100

101
102
103
104
105
106
107
108
109
110
########################################################################
#
# Grammar and parsing infrastructure
#
########################################################################


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


111
LEFT_RECURSION_DEPTH = 10  # because of pythons recursion depth limit, this
Eckhart Arnold's avatar
Eckhart Arnold committed
112
                           # value ought not to be set too high
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
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

140
    def err_msg(self) -> str:
141
142
        return self.ERROR + ": " + "; ".join(self.node._errors).replace('\n', '\\')

143
    @property
144
    def stack(self) -> str:
145
146
147
        return "->".join(str(parser) for parser in self.call_stack)

    @property
148
    def status(self) -> str:
149
150
        return self.FAIL if self.node is None else \
            self.err_msg() if self.node._errors else self.MATCH
151
152

    @property
153
    def extent(self) -> Tuple[int, int]:
154
155
156
157
158
        return ((-self.remaining - self.node.len, -self.remaining) if self.node
                else (-self.remaining, None))


def add_parser_guard(parser_func):
159
    def guarded_call(parser: 'Parser', text: str) -> Tuple[Node, str]:
160
161
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
            grammar = parser.grammar

173
            if grammar.history_tracking:
174
175
176
177
178
179
                grammar.call_stack.append(parser)
                grammar.moving_forward = True

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

180
            if grammar.history_tracking:
181
182
                # don't track returning parsers except in case an error has occurred
                if grammar.moving_forward or (node and node._errors):
183
184
185
                    grammar.moving_forward = False
                    record = HistoryRecord(grammar.call_stack.copy(), node, len(rest))
                    grammar.history.append(record)
186
                    # print(record.stack, record.status, rest[:20].replace('\n', '|'))
187
188
189
190
191
192
                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)
193
                grammar.last_node = node   # store last node for Lookbehind operator
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
            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


class ParserMetaClass(type):
    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)


class Parser(metaclass=ParserMetaClass):
225
226
    ApplyFunc = Callable[['Parser'], None]

227
    def __init__(self, name=''):
228
        assert isinstance(name, str), str(name)
229
230
        self.name = name  # type: str
        self._grammar = None  # type: 'Grammar'
231
232
        self.reset()

Eckhart Arnold's avatar
Eckhart Arnold committed
233
    def __deepcopy__(self, memo):
234
235
236
        return self.__class__(self.name)

    @property
237
    def ptype(self) -> str:
238
        return ':' + self.__class__.__name__
Eckhart Arnold's avatar
Eckhart Arnold committed
239

240
    def reset(self):
241
242
243
        self.visited = dict()  # type: Dict[int, Tuple[Node, str]]
        self.recursion_counter = dict()  # type: Dict[int, int]
        self.cycle_detection = set()  # type: Set[Callable]
244
        return self
245

246
    def __call__(self, text: str) -> Tuple[Node, str]:
247
248
249
        return None, text  # default behaviour: don't match

    def __str__(self):
250
        return self.name or self.ptype
251

252
253
254
255
256
257
    def __add__(self, other):
        return Sequence(self, other)

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

258
    @property
259
    def grammar(self) -> 'Grammar':
260
261
262
        return self._grammar

    @grammar.setter
263
264
    def grammar(self, grammar: 'Grammar'):
        self._grammar = grammar
265
266
267
268
269
        self._grammar_assigned_notifier()

    def _grammar_assigned_notifier(self):
        pass

270
    def apply(self, func: ApplyFunc):
271
        """Applies function `func(parser)` recursively to this parser and all
Eckhart Arnold's avatar
Eckhart Arnold committed
272
        descendants of the tree of parsers. The same function can never
273
274
275
276
277
278
279
280
281
282
        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


283
class Grammar:
284
285
    root__ = None  # type: Union[Parser, None]
    # root__ must be overwritten with the root-parser by grammar subclass
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"

318
319
320
321
322
323
324
    def __init__(self, root=None):
        if not hasattr(self.__class__, 'parser_initialization__'):
            self.__class__.parser_initialization__ = "pending"
        if not hasattr(self.__class__, 'wspL__'):
            self.wspL__ = ''
        if not hasattr(self.__class__, 'wspR__'):
            self.wspR__ = ''
325
326
        self.all_parsers = set()
        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__:
332
            self.wsp_left_parser__ = Whitespace(self.wspL__)
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__:
338
            self.wsp_right_parser__ = Whitespace(self.wspR__)
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
361
        # 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

    def _add_parser(self, parser: Parser):
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, start_parser="root__"):
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.
        """
Eckhart Arnold's avatar
Eckhart Arnold committed
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
392
        parser = self[start_parser]
393
394
        stitches = []
        rest = document
395
396
        if not rest:
            result, ignore = parser(rest)
397
398
399
400
401
402
403
404
405
406
        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" + \
407
408
409
                                (("! trying to recover" +
                                  (" but stopping history recording at this point."
                                   if self.history_tracking else "..."))
410
411
412
413
                                 if len(stitches) < MAX_DROPOUTS
                                 else " too often! Terminating parser.")
                stitches.append(Node(None, skip))
                stitches[-1].add_error(error_msg)
414
415
416
417
                if self.history_tracking:
                    record = HistoryRecord(self.call_stack.copy(), stitches[-1], len(rest))
                    self.history.append(record)
                    self.history_tracking = False
418
419
420
421
422
423
424
        if stitches:
            if rest:
                stitches.append(Node(None, rest))
            result = Node(None, tuple(stitches))
        result.pos = 0  # calculate all positions
        return result

425
    def log_parsing_history(self, log_file_name=''):
426
427
428
429
430
431
        """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
432
            return record.stack, record.status, excerpt
433
434

        def write_log(history, log_name):
Eckhart Arnold's avatar
Eckhart Arnold committed
435
            path = os.path.join(log_dir(), log_name + "_parser.log")
436
437
438
439
440
441
            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
442
443
444
445
446
447
448
        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)
449
            if record.node and record.node.parser.ptype != WHITESPACE_PTYPE:
Eckhart Arnold's avatar
Eckhart Arnold committed
450
451
452
453
454
455
                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')
456
457


458
def dsl_error_msg(parser, error_str) -> str:
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
    """Returns an error messsage for errors in the parser configuration,
    e.g. errors that result in infinite loops.

    Args:
        parser (Parser:  The parser where the error was noticed. Note
            that this is not necessarily the parser that caused the
            error but only where the error became apparaent.
        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)


479
480
481
482
483
484
485
486
487
488
489
490
########################################################################
#
# Token and Regular Expression parser classes (i.e. leaf classes)
#
########################################################################


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


491
def make_token(token, argument='') -> str:
492
493
494
495
496
497
498
499
500
501
502
503
504
    """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


505
def nil_scanner(text) -> str:
Eckhart Arnold's avatar
Eckhart Arnold committed
506
    return text
507
508
509


class ScannerToken(Parser):
510
511
512
513
514
515
516
517
518
519
    """
    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.
    """
520
    def __init__(self, scanner_token):
521
522
523
        assert isinstance(scanner_token, str) and scanner_token and \
               scanner_token.isupper()
        assert RX_SCANNER_TOKEN.match(scanner_token)
524
        super(ScannerToken, self).__init__(scanner_token)
525

526
    def __call__(self, text: str) -> Tuple[Node, str]:
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
        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):
553
554
    """
    Regular expression parser.
555
556
557
558
559
560
    
    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.
    """
561
562
    def __init__(self, regexp, name=''):
        super(RegExp, self).__init__(name)
563
564
565
        self.regexp = re.compile(regexp) if isinstance(regexp, str) else regexp

    def __deepcopy__(self, memo):
Eckhart Arnold's avatar
Eckhart Arnold committed
566
        # `regex` supports deep copies, but not `re`
567
        try:
Eckhart Arnold's avatar
Eckhart Arnold committed
568
            regexp = copy.deepcopy(self.regexp, memo)
569
570
        except TypeError:
            regexp = self.regexp.pattern
571
        return RegExp(regexp, self.name)
572

573
    def __call__(self, text: str) -> Tuple[Node, str]:
574
575
576
577
578
579
        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

580
581
582
    def __str__(self):
        return self.name or self.ptype + ' /%s/' % self.regexp.pattern

583

584
585
class Whitespace(RegExp):
    assert WHITESPACE_PTYPE == ":Whitespace"
586
587


588
589
class RE(Parser):
    """Regular Expressions with optional leading or trailing whitespace.
590
591
592
593
594
595
596
597
598
599
    
    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.
600
    """
601
    def __init__(self, regexp, wL=None, wR=None, name=''):
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
        """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.
        """
617
        super(RE, self).__init__(name)
618
619
        self.wL = wL
        self.wR = wR
620
621
        self.wspLeft = Whitespace(wL) if wL else ZOMBIE_PARSER
        self.wspRight = Whitespace(wR) if wR else ZOMBIE_PARSER
622
623
        self.main = RegExp(regexp)

Eckhart Arnold's avatar
Eckhart Arnold committed
624
625
626
627
628
    def __deepcopy__(self, memo={}):
        try:
            regexp = copy.deepcopy(self.main.regexp, memo)
        except TypeError:
            regexp = self.main.regexp.pattern
629
        return self.__class__(regexp, self.wL, self.wR, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
630

631
    def __call__(self, text: str) -> Tuple[Node, str]:
632
633
634
635
636
637
638
639
640
641
642
        # 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

643
    def __str__(self):
644
        if self.ptype == TOKEN_PTYPE:
645
646
647
            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 ''))
648
649
650

    def _grammar_assigned_notifier(self):
        if self.grammar:
651
            # use default whitespace parsers if not otherwise specified
652
653
654
655
656
            if self.wL is None:
                self.wspLeft = self.grammar.wsp_left_parser__
            if self.wR is None:
                self.wspRight = self.grammar.wsp_right_parser__

657
    def apply(self, func: Parser.ApplyFunc):
658
659
660
661
662
663
664
665
        if super(RE, self).apply(func):
            if self.wL:
                self.wspLeft.apply(func)
            if self.wR:
                self.wspRight.apply(func)
            self.main.apply(func)


666
667
668
669
670
671
672
673
674
class Token(RE):
    assert TOKEN_PTYPE == ":Token"

    def __init__(self, token, wL=None, wR=None, name=''):
        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)
675
676
677


def mixin_comment(whitespace, comment):
678
679
680
681
682
683
684
    """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).
685
686
687
688
689
690
691
692
693
694
695
696
697
    """
    wspc = '(?:' + whitespace + '(?:' + comment + whitespace + ')*)'
    return wspc


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


class UnaryOperator(Parser):
698
699
    def __init__(self, parser, name=''):
        super(UnaryOperator, self).__init__(name)
700
        assert isinstance(parser, Parser)
701
        self.parser = parser  # type: Parser
702

Eckhart Arnold's avatar
Eckhart Arnold committed
703
704
    def __deepcopy__(self, memo):
        parser = copy.deepcopy(self.parser, memo)
705
        return self.__class__(parser, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
706

707
    def apply(self, func: Parser.ApplyFunc):
708
709
710
711
712
        if super(UnaryOperator, self).apply(func):
            self.parser.apply(func)


class NaryOperator(Parser):
713
714
    def __init__(self, *parsers, name=''):
        super(NaryOperator, self).__init__(name)
715
        assert all([isinstance(parser, Parser) for parser in parsers]), str(parsers)
716
        self.parsers = parsers  # type: List[Parser]
717

Eckhart Arnold's avatar
Eckhart Arnold committed
718
719
    def __deepcopy__(self, memo):
        parsers = copy.deepcopy(self.parsers, memo)
720
        return self.__class__(*parsers, name=self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
721

722
    def apply(self, func: Parser.ApplyFunc):
723
724
725
726
727
728
        if super(NaryOperator, self).apply(func):
            for parser in self.parsers:
                parser.apply(func)


class Optional(UnaryOperator):
729
730
    def __init__(self, parser, name=''):
        super(Optional, self).__init__(parser, name)
731
732
733
734
735
        assert isinstance(parser, Parser)
        assert not isinstance(parser, Optional), \
            "Nesting options would be redundant: %s(%s)" % \
            (str(name), str(parser.name))
        assert not isinstance(parser, Required), \
736
            "Nesting options with required elements is contradictory: " \
737
738
            "%s(%s)" % (str(name), str(parser.name))

739
    def __call__(self, text: str) -> Tuple[Node, str]:
740
741
742
743
744
745
746
        node, text = self.parser(text)
        if node:
            return Node(self, node), text
        return Node(self, ()), text


class ZeroOrMore(Optional):
747
748
    def __call__(self, text: str) -> Tuple[Node, str]:
        results = ()  # type: Tuple[Node, ...]
749
750
751
        n = len(text) + 1
        while text and len(text) < n:
            n = len(text)
752
753
754
            node, text = self.parser(text)
            if not node:
                break
755
            if len(text) == n:
di68kap's avatar
di68kap committed
756
                node.add_error(dsl_error_msg(self, 'Infinite Loop detected.'))
757
758
759
760
761
            results += (node,)
        return Node(self, results), text


class OneOrMore(UnaryOperator):
762
763
    def __init__(self, parser, name=''):
        super(OneOrMore, self).__init__(parser, name)
764
765
766
767
        assert not isinstance(parser, Optional), \
            "Use ZeroOrMore instead of nesting OneOrMore and Optional: " \
            "%s(%s)" % (str(name), str(parser.name))

768
769
770
    def __call__(self, text: str) -> Tuple[Node, str]:
        results = ()  # type: Tuple[Node, ...]
        text_ = text  # type: str
771
772
773
        n = len(text) + 1
        while text_ and len(text_) < n:
            n = len(text_)
774
775
776
            node, text_ = self.parser(text_)
            if not node:
                break
777
            if len(text_) == n:
778
                node.add_error(dsl_error_msg(self, 'Infinite Loop detected.'))
779
780
781
782
783
784
785
            results += (node,)
        if results == ():
            return None, text
        return Node(self, results), text_


class Sequence(NaryOperator):
786
787
    def __init__(self, *parsers, name=''):
        super(Sequence, self).__init__(*parsers, name=name)
788
789
        assert len(self.parsers) >= 1

790
791
792
    def __call__(self, text: str) -> Tuple[Node, str]:
        results = ()  # type: Tuple[Node, ...]
        text_ = text  # type: str
793
794
795
796
797
798
799
800
801
802
803
        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_

804
805
806
807
808
809
810
811
812
813
814
815
816
    def __add__(self, other):
        return Sequence(*self.parsers, other)

    def __radd__(self, other):
        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

817
818

class Alternative(NaryOperator):
819
820
821
822
823
824
825
826
827
828
829
830
    """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.

    # the order of the sub-expression matters:

    # the most selective expression should be put first:

    """
831
832
    def __init__(self, *parsers, name=''):
        super(Alternative, self).__init__(*parsers, name=name)
833
834
835
        assert len(self.parsers) >= 1
        assert all(not isinstance(p, Optional) for p in self.parsers)

836
    def __call__(self, text: str) -> Tuple[Node, str]:
837
838
839
840
841
842
        for parser in self.parsers:
            node, text_ = parser(text)
            if node:
                return Node(self, node), text_
        return None, text

843
844
845
846
847
848
849
850
851
852
853
854
855
    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

856
857
858
859
860
861
862
863
864

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


class FlowOperator(UnaryOperator):
865
866
    def __init__(self, parser, name=''):
        super(FlowOperator, self).__init__(parser, name)
867
868
869


class Required(FlowOperator):
870
    # Add constructor that checks for logical errors, like `Required(Optional(...))` constructs ?
871
    def __call__(self, text: str) -> Tuple[Node, str]:
872
873
874
875
876
877
878
879
880
881
882
883
884
        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):
885
886
    def __init__(self, parser, name=''):
        super(Lookahead, self).__init__(parser, name)
887

888
    def __call__(self, text: str) -> Tuple[Node, str]:
889
890
891
892
893
894
        node, text_ = self.parser(text)
        if self.sign(node is not None):
            return Node(self, ''), text
        else:
            return None, text

895
    def sign(self, bool_value) -> bool:
896
897
898
899
        return bool_value


class NegativeLookahead(Lookahead):
900
    def sign(self, bool_value) -> bool:
901
902
903
        return not bool_value


904
def iter_right_branch(node) -> Iterator[Node]:
905
906
907
908
909
910
911
912
913
914
915
916
    """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):
917
918
    def __init__(self, parser, name=''):
        super(Lookbehind, self).__init__(parser, name)
919
920
        print("WARNING: Lookbehind Operator is experimental!")

921
    def __call__(self, text: str) -> Tuple[Node, str]:
922
923
924
925
926
927
928
929
        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

930
    def sign(self, bool_value) -> bool:
931
932
933
934
935
936
937
938
939
940
941
942
943
944
        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):
945
    def sign(self, bool_value) -> bool:
946
947
948
949
950
951
952
953
954
955
956
        return not bool_value


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


class Capture(UnaryOperator):
957
958
    def __init__(self, parser, name=''):
        super(Capture, self).__init__(parser, name)
959

960
    def __call__(self, text: str) -> Tuple[Node, str]:
961
962
963
964
        node, text = self.parser(text)
        if node:
            stack = self.grammar.variables.setdefault(self.name, [])
            stack.append(str(node))
965
966
967
            return Node(self, node), text
        else:
            return None, text
968
969


970
971
972
973
974
975
976
977
978
979
980
981
982
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)


983
class Retrieve(Parser):
984
    def __init__(self, symbol, retrieve_filter=None, name=''):
985
986
        if not name:
            name = symbol.name
987
        super(Retrieve, self).__init__(name)
988
        self.symbol = symbol
989
        self.retrieve_filter = retrieve_filter if retrieve_filter else nop_filter
990

Eckhart Arnold's avatar
Eckhart Arnold committed
991
    def __deepcopy__(self, memo):
992
        return self.__class__(self.symbol, self.retrieve_filter, self.name)
Eckhart Arnold's avatar
Eckhart Arnold committed
993

994
    def __call__(self, text: str) -> Tuple[Node, str]:
995
996
997
998
999
1000
1001
        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
1002
1003
1004
1005
1006
        if text.startswith(value):
            return Node(self, value), text[len(value):]
        else:
            return None, text

1007
    def pick_value(self, stack: List[str]) -> str:
1008
1009
1010
1011
        return stack[-1]


class Pop(Retrieve):
1012
    def pick_value(self, stack: List[str]) -> str:
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
        return stack.pop()


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


class Forward(Parser):
    def __init__(self):
        Parser.__init__(self)
        self.parser = None
1027
        self.cycle_reached = False
1028

Eckhart Arnold's avatar
Eckhart Arnold committed
1029
1030
1031
1032
1033
1034
1035
    def __deepcopy__(self, memo):
        duplicate = self.__class__()
        memo[id(self)] = duplicate
        parser = copy.deepcopy(self.parser, memo)
        duplicate.set(parser)
        return duplicate

1036
    def __call__(self, text: str) -> Tuple[Node, str]:
1037
1038
        return self.parser(text)

1039
1040
1041
1042
1043
1044
1045
1046
    def __str__(self):
        if self.cycle_reached:
            return "..."
        else:
            self.cycle_reached = True
            s = str(self.parser)
            self.cycle_reached = False
            return s
1047

1048
1049
    def set(self, parser: Parser):
        # assert isinstance(parser, Parser)
1050
        self.name = parser.name  # redundant, see Grammar-constructor
1051
1052
        self.parser = parser

1053
    def apply(self, func: Parser.ApplyFunc):
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
        if super(Forward, self).apply(func):
            assert not self.visited
            self.parser.apply(func)


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


1066
class Compiler:
Eckhart Arnold's avatar
Eckhart Arnold committed
1067
    def __init__(self, grammar_name="", grammar_source=""):
1068
        self.dirty_flag = False
Eckhart Arnold's avatar
Eckhart Arnold committed
1069
        self.set_grammar_name(grammar_name, grammar_source)
1070
1071
1072
1073

    def _reset(self):
        pass

1074
    def __call__(self, node: Node) -> Any:
1075
        """Compiles the abstract syntax tree with the root ``node``.
1076
        
Eckhart Arnold's avatar
Eckhart Arnold committed
1077
        It's called `compile_ast`` to avoid confusion with the 
1078
1079
        ``_compile`` that is called from within the local node 
        compiler methods.
1080
1081
1082
1083
1084
1085
1086
        """
        if self.dirty_flag:
            self._reset()
        else:
            self.dirty_flag = True
        return self._compile(node)

Eckhart Arnold's avatar
Eckhart Arnold committed
1087
1088
1089
1090
1091
1092
1093
    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)

1094
    @staticmethod
1095
    def derive_method_name(node_name: str) -> str:
1096
        """Returns the method name for ``node_name``, e.g.
1097
        >>> Compiler.method_name('expression')
1098
1099
1100
1101
        'on_expression'
        """
        return 'on_' + node_name

1102
    def _compile(self, node: Node) -> Any:
1103
1104
1105
1106
1107
        """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
1108
        name by adding the prefix 'on_'.
1109
1110
1111
1112
1113
        
        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.
        """
1114
        elem = node.parser.name or node.parser.ptype[1:]
1115
        if not sane_parser_name(elem):
1116
            node.add_error("Reserved name '%s' not allowed as parser "
1117
                           "name! " % elem + "(Any name starting with "
1118
                           "'_' or '__' or ending with '__' is reserved.)")
1119
1120
            return None
        else:
1121
            compiler = self.__getattribute__(self.derive_method_name(elem))
1122
1123
            result = compiler(node)
            for child in node.children:
1124
                node.error_flag = node.error_flag or child.error_flag
1125
            return result
1126
1127


1128
1129
1130
1131
1132
def compile_source(source: str,
                   scanner: ScannerFunc,  # str -> str
                   parser: Grammar,  # str -> Node (concrete syntax tree (CST))
                   transformer: TransformerFunc,  # Node -> Node (abstract syntax tree (AST))
                   compiler: Compiler):         # Node (AST) -> Any
1133
1134
1135
1136
1137
    """Compiles a source in four stages:
        1. Scanning (if needed)
        2. Parsing
        3. AST-transformation
        4. Compiling.
1138
1139
1140
    The compilations stage is only invoked if no errors occurred in
    either of the two previous stages.

1141
    Args:
1142
1143
        source (str): The input text for compilation or a the name of a
            file containing the input text.
Eckhart Arnold's avatar
Eckhart Arnold committed
1144
        scanner (function):  text -> text. A scanner function or None,
1145
            if no scanner is needed.
Eckhart Arnold's avatar
Eckhart Arnold committed
1146
1147
        parser (function):  A parsing function or grammar class 
        transformer (function):  A transformation function that takes
1148
1149
            the root-node of the concrete syntax tree as an argument and
            transforms it (in place) into an abstract syntax tree.
Eckhart Arnold's avatar
Eckhart Arnold committed
1150
        compiler (function): A compiler function or compiler class
Eckhart Arnold's avatar
Eckhart Arnold committed
1151
            instance 
1152
1153
1154
1155
1156
1157

    Returns (tuple):
        The result of the compilation as a 3-tuple
        (result, errors, abstract syntax tree). In detail:
        1. The result as returned by the compiler or ``None`` in case
            of failure,
1158
        2. A list of error messages
1159
        3. The root-node of the abstract syntax treelow
1160
    """
1161
    source_text = load_if_file(source)
Eckhart Arnold's avatar
Eckhart Arnold committed
1162
1163
1164
1165
    log_file_name = logfile_basename(source, compiler)
    if scanner is not None:
        source_text = scanner(source_text)
    syntax_tree = parser(source_text)
Eckhart Arnold's avatar
Eckhart Arnold committed
1166
    if is_logging():
Eckhart Arnold's avatar
Eckhart Arnold committed
1167
        syntax_tree.log(log_file_name + '.cst')
1168
        parser.log_parsing_history(log_file_name)
1169

1170
    assert syntax_tree.error_flag or str(syntax_tree) == source_text, str(syntax_tree)
1171
1172
1173
1174
    # only compile if there were no syntax errors, for otherwise it is
    # likely that error list gets littered with compile error messages
    if syntax_tree.error_flag:
        result = None
1175
        errors = syntax_tree.collect_errors()
1176
    else:
Eckhart Arnold's avatar
Eckhart Arnold committed
1177
1178
        transformer(syntax_tree)
        if is_logging():  syntax_tree.log(log_file_name + '.ast')
1179
1180
        errors = syntax_tree.collect_errors()
        if not errors:
Eckhart Arnold's avatar
Eckhart Arnold committed
1181
            result = compiler(syntax_tree)
1182
            errors = syntax_tree.collect_errors() if syntax_tree.error_flag else []
1183
    messages = error_messages(source_text, errors)
1184