2.12.2021, 9:00 - 11:00: Due to updates GitLab may be unavailable for some minutes between 09:00 and 11:00.

ebnf.py 29.8 KB
Newer Older
1
"""ebnf.py - EBNF -> Python-Parser compilation for DHParser
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

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.
"""

19
import keyword
20
21
from collections import OrderedDict

22
23
24
25
try:
    import regex as re
except ImportError:
    import re
26
from typing import Callable, Dict, List, Set, Tuple
27

28
from DHParser.toolkit import load_if_file, escape_re, md5, sane_parser_name, warnings
29
30
31
32
from DHParser.parsers import Grammar, mixin_comment, nil_scanner, Forward, RE, NegativeLookahead, \
    Alternative, Sequence, Optional, Required, OneOrMore, ZeroOrMore, Token, Compiler, \
    ScannerFunc
from DHParser.syntaxtree import Node, traverse, remove_enclosing_delimiters, reduce_single_child, \
33
    replace_by_single_child, TOKEN_PTYPE, remove_expendables, remove_tokens, flatten, \
34
    forbid, assert_content, WHITESPACE_PTYPE, key_tag_name, TransformationFunc
35
from DHParser.versionnumber import __version__
36
37


38
39
40
41
42
__all__ = ['get_ebnf_scanner',
           'get_ebnf_grammar',
           'get_ebnf_transformer',
           'get_ebnf_compiler',
           'EBNFGrammar',
43
           'EBNFTransformer',
Eckhart Arnold's avatar
Eckhart Arnold committed
44
           'EBNFCompilerError',
45
           'EBNFCompiler',
46
47
48
49
50
           'grammar_changed',
           'ScannerFactoryFunc',
           'ParserFactoryFunc',
           'TransformerFactoryFunc',
           'CompilerFactoryFunc']
51
52


Eckhart Arnold's avatar
Eckhart Arnold committed
53
54
55
56
57
58
59
########################################################################
#
# EBNF scanning
#
########################################################################


60
def get_ebnf_scanner() -> ScannerFunc:
Eckhart Arnold's avatar
Eckhart Arnold committed
61
62
63
64
65
66
67
68
69
    return nil_scanner


########################################################################
#
# EBNF parsing
#
########################################################################

70
71
# TODO: Introduce dummy/rename-parser, for simple assignments (e.g. jahr = JAHRESZAHL) or substition!
# TODO: Raise Error for unconnected parsers!
72
class EBNFGrammar(Grammar):
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
    r"""Parser for an EBNF source file, with this grammar:

    # EBNF-Grammar in EBNF

    @ comment    =  /#.*(?:\n|$)/                    # comments start with '#' and eat all chars up to and including '\n'
    @ whitespace =  /\s*/                            # whitespace includes linefeed
    @ literalws  =  right                            # trailing whitespace of literals will be ignored tacitly

    syntax     =  [~//] { definition | directive } §EOF
    definition =  symbol §"=" expression
    directive  =  "@" §symbol §"=" ( regexp | literal | list_ )

    expression =  term { "|" term }
    term       =  { factor }+
    factor     =  [flowmarker] [retrieveop] symbol !"="   # negative lookahead to be sure it's not a definition
                | [flowmarker] literal
                | [flowmarker] regexp
                | [flowmarker] group
91
                | [flowmarker] regexchain
92
93
94
95
96
97
98
99
100
                | [flowmarker] oneormore
                | repetition
                | option

    flowmarker =  "!"  | "&"  | "§" |                # '!' negative lookahead, '&' positive lookahead, '§' required
                  "-!" | "-&"                        # '-' negative lookbehind, '-&' positive lookbehind
    retrieveop =  "::" | ":"                         # '::' pop, ':' retrieve

    group      =  "(" expression §")"
101
    regexchain =  ">" expression §"<"                # compiles "expression" into a singular regular expression
102
103
    oneormore  =  "{" expression "}+"
    repetition =  "{" expression §"}"
104
105
    option     =  "[" expression §"]"

106
107
108
109
110
111
    symbol     =  /(?!\d)\w+/~                       # e.g. expression, factor, parameter_list
    literal    =  /"(?:[^"]|\\")*?"/~                # e.g. "(", '+', 'while'
                | /'(?:[^']|\\')*?'/~                # whitespace following literals will be ignored tacitly.
    regexp     =  /~?\/(?:[^\/]|(?<=\\)\/)*\/~?/~    # e.g. /\w+/, ~/#.*(?:\n|$)/~
                                                     # '~' is a whitespace-marker, if present leading or trailing
                                                     # whitespace of a regular expression will be ignored tacitly.
112
    list_      =  /\w+/~ { "," /\w+/~ }              # comma separated list of symbols, e.g. BEGIN_LIST, END_LIST,
113
114
115
116
                                                     # BEGIN_QUOTE, END_QUOTE ; see CommonMark/markdown.py for an exmaple
    EOF =  !/./
    """
    expression = Forward()
117
    source_hash__ = "a410e1727fb7575e98ff8451dbf8f3bd"
118
    parser_initialization__ = "upon instantiation"
119
120
    COMMENT__ = r'#.*(?:\n|$)'
    WSP__ = mixin_comment(whitespace=r'\s*', comment=r'#.*(?:\n|$)')
121
    wspL__ = ''
122
    wspR__ = WSP__
123
    EOF = NegativeLookahead(RE('.', wR=''))
124
    list_ = Sequence(RE('\\w+'), ZeroOrMore(Sequence(Token(","), RE('\\w+'))))
125
126
127
    regexp = RE('~?/(?:[^/]|(?<=\\\\)/)*/~?')
    literal = Alternative(RE('"(?:[^"]|\\\\")*?"'), RE("'(?:[^']|\\\\')*?'"))
    symbol = RE('(?!\\d)\\w+')
128
    option = Sequence(Token("["), expression, Required(Token("]")))
129
130
    repetition = Sequence(Token("{"), expression, Required(Token("}")))
    oneormore = Sequence(Token("{"), expression, Token("}+"))
131
    regexchain = Sequence(Token("<"), expression, Required(Token(">")))
132
133
134
135
136
    group = Sequence(Token("("), expression, Required(Token(")")))
    retrieveop = Alternative(Token("::"), Token(":"))
    flowmarker = Alternative(Token("!"), Token("&"), Token("§"), Token("-!"), Token("-&"))
    factor = Alternative(Sequence(Optional(flowmarker), Optional(retrieveop), symbol, NegativeLookahead(Token("="))),
                         Sequence(Optional(flowmarker), literal), Sequence(Optional(flowmarker), regexp),
137
138
                         Sequence(Optional(flowmarker), group), Sequence(Optional(flowmarker), regexchain),
                         Sequence(Optional(flowmarker), oneormore), repetition, option)
139
140
141
142
    term = OneOrMore(factor)
    expression.set(Sequence(term, ZeroOrMore(Sequence(Token("|"), term))))
    directive = Sequence(Token("@"), Required(symbol), Required(Token("=")), Alternative(regexp, literal, list_))
    definition = Sequence(symbol, Required(Token("=")), expression)
143
    syntax = Sequence(Optional(RE('', wR='', wL=WSP__)), ZeroOrMore(Alternative(definition, directive)), Required(EOF))
144
145
146
    root__ = syntax


147
def grammar_changed(grammar_class, grammar_source: str) -> bool:
Eckhart Arnold's avatar
Eckhart Arnold committed
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
    """Returns ``True`` if ``grammar_class`` does not reflect the latest
    changes of ``grammar_source``

    Parameters:
        grammar_class:  the parser class representing the grammar
            or the file name of a compiler suite containing the grammar
        grammar_source:  File name or string representation of the
            EBNF code of the grammar

    Returns (bool):
        True, if the source text of the grammar is different from the
        source from which the grammar class was generated
    """
    grammar = load_if_file(grammar_source)
    chksum = md5(grammar, __version__)
    if isinstance(grammar_class, str):
        # grammar_class = load_compiler_suite(grammar_class)[1]
        with open(grammar_class, 'r', encoding='utf8') as f:
            pycode = f.read()
167
        m = re.search('class \w*\(Grammar\)', pycode)
Eckhart Arnold's avatar
Eckhart Arnold committed
168
169
170
171
172
173
174
175
176
177
        if m:
            m = re.search('    source_hash__ *= *"([a-z0-9]*)"',
                          pycode[m.span()[1]:])
            return not (m and m.groups() and m.groups()[-1] == chksum)
        else:
            return True
    else:
        return chksum != grammar_class.source_hash__


178
def get_ebnf_grammar() -> EBNFGrammar:
Eckhart Arnold's avatar
Eckhart Arnold committed
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
    global thread_local_ebnf_grammar_singleton
    try:
        grammar = thread_local_ebnf_grammar_singleton
        return grammar
    except NameError:
        thread_local_ebnf_grammar_singleton = EBNFGrammar()
        return thread_local_ebnf_grammar_singleton


########################################################################
#
# EBNF concrete to abstract syntax tree transformation and validation
#
########################################################################


195
196
#TODO: Add Capture and Retrieve Validation: A variable mustn't be captured twice before retrival?!?

197
EBNF_transformation_table = {
198
199
200
201
    # AST Transformations for EBNF-grammar
    "syntax":
        remove_expendables,
    "directive, definition":
202
        remove_tokens('@', '='),
Eckhart Arnold's avatar
Eckhart Arnold committed
203
    "expression":
204
        [replace_by_single_child, flatten, remove_tokens('|')],
205
206
207
208
209
    "term":
        [replace_by_single_child, flatten],  # supports both idioms:  "{ factor }+" and "factor { factor }"
    "factor, flowmarker, retrieveop":
        replace_by_single_child,
    "group":
210
211
212
        [remove_enclosing_delimiters, replace_by_single_child],
    "oneormore, repetition, option, regexchain":
        [reduce_single_child, remove_enclosing_delimiters],
213
    "symbol, literal, regexp":
214
        [remove_expendables, reduce_single_child],
215
    (TOKEN_PTYPE, WHITESPACE_PTYPE):
216
        [remove_expendables, reduce_single_child],
217
    "list_":
218
        [flatten, remove_tokens(',')],
219
    "*":
220
221
222
        [remove_expendables, replace_by_single_child]
}

223

224
EBNF_validation_table = {
225
    # Semantic validation on the AST. EXPERIMENTAL!
226
    "repetition, option, oneormore":
227
228
        [forbid('repetition', 'option', 'oneormore'),
         assert_content(r'(?!§)')]
229
}
230

231

232
def EBNFTransformer(syntax_tree: Node):
233
    for processing_table, key_func in [(EBNF_transformation_table, key_tag_name),
234
                                       (EBNF_validation_table, key_tag_name)]:
235
        traverse(syntax_tree, processing_table, key_func)
di68kap's avatar
di68kap committed
236
237


238
def get_ebnf_transformer() -> TransformationFunc:
239
    return EBNFTransformer
Eckhart Arnold's avatar
Eckhart Arnold committed
240
241
242
243
244
245
246
247


########################################################################
#
# EBNF abstract syntax tree to Python parser compilation
#
########################################################################

248
249
250

ScannerFactoryFunc = Callable[[], ScannerFunc]
ParserFactoryFunc = Callable[[], Grammar]
251
TransformerFactoryFunc = Callable[[], TransformationFunc]
252
253
254
CompilerFactoryFunc = Callable[[], Compiler]


255
SCANNER_FACTORY = '''
256
def get_scanner() -> ScannerFunc:
257
258
259
260
261
    return {NAME}Scanner
'''


GRAMMAR_FACTORY = '''
262
def get_grammar() -> {NAME}Grammar:
263
264
265
266
267
268
269
270
271
272
273
    global thread_local_{NAME}_grammar_singleton
    try:
        grammar = thread_local_{NAME}_grammar_singleton
        return grammar
    except NameError:
        thread_local_{NAME}_grammar_singleton = {NAME}Grammar()
        return thread_local_{NAME}_grammar_singleton
'''


TRANSFORMER_FACTORY = '''
274
def get_transformer() -> TransformationFunc:
275
276
277
278
279
    return {NAME}Transform
'''


COMPILER_FACTORY = '''
280
def get_compiler(grammar_name="{NAME}", grammar_source="") -> {NAME}Compiler:
281
282
283
284
285
286
287
288
289
290
291
    global thread_local_{NAME}_compiler_singleton
    try:
        compiler = thread_local_{NAME}_compiler_singleton
        compiler.set_grammar_name(grammar_name, grammar_source)
        return compiler
    except NameError:
        thread_local_{NAME}_compiler_singleton = \\
            {NAME}Compiler(grammar_name, grammar_source)
        return thread_local_{NAME}_compiler_singleton 
'''

Eckhart Arnold's avatar
Eckhart Arnold committed
292

293
294
class EBNFCompilerError(Exception):
    """Error raised by `EBNFCompiler` class. (Not compilation errors
295
    in the strict sense, see `CompilationError` in module ``dsl.py``)"""
296
297
298
    pass


299
class EBNFCompiler(Compiler):
300
301
302
303
    """Generates a Parser from an abstract syntax tree of a grammar specified
    in EBNF-Notation.
    """
    COMMENT_KEYWORD = "COMMENT__"
304
305
    WHITESPACE_KEYWORD = "WSP__"
    RESERVED_SYMBOLS = {WHITESPACE_KEYWORD, COMMENT_KEYWORD}
306
307
    AST_ERROR = "Badly structured syntax tree. " \
                "Potentially due to erroneuos AST transformation."
308
309
310
311
    PREFIX_TABLE = {'§': 'Required',
                    '&': 'Lookahead', '!': 'NegativeLookahead',
                    '-&': 'Lookbehind', '-!': 'NegativeLookbehind',
                    '::': 'Pop', ':': 'Retrieve'}
312
313
314
    WHITESPACE = {'horizontal': r'[\t ]*',  # default: horizontal
                  'linefeed': r'[ \t]*\n?(?!\s*\n)[ \t]*',
                  'vertical': r'\s*'}
315

316
    def __init__(self, grammar_name="", grammar_source=""):
Eckhart Arnold's avatar
Eckhart Arnold committed
317
        super(EBNFCompiler, self).__init__(grammar_name, grammar_source)
318
319
320
        self._reset()

    def _reset(self):
321
        self._result = ''           # type: str
322
323
324
        self.rules = OrderedDict()  # type: OrderedDict[str, List[Node]]
        self.current_symbols = []   # type: List[Node]
        self.symbols = {}           # type: Dict[str, Node]
325
        self.variables = set()      # type: Set[str]
326
        # self.definition_names = []  # type: List[str]
327
328
        self.recursive = set()      # type: Set[str]
        self.root = ""              # type: str
329
        self.directives = {'whitespace': self.WHITESPACE['horizontal'],
330
                           'comment': '',
331
                           'literalws': ['right'],
332
333
                           'tokens': set(),  # alt. 'scanner_tokens'
                           'filter': dict()}  # alt. 'filter'
334

Eckhart Arnold's avatar
Eckhart Arnold committed
335
    @property
336
    def result(self) -> str:
Eckhart Arnold's avatar
Eckhart Arnold committed
337
338
        return self._result

339
    def gen_scanner_skeleton(self) -> str:
340
        name = self.grammar_name + "Scanner"
341
342
        return "def %s(text):\n    return text\n" % name \
               + SCANNER_FACTORY.format(NAME=self.grammar_name)
343

344
    def gen_transformer_skeleton(self) -> str:
345
        if not self.rules:
Eckhart Arnold's avatar
Eckhart Arnold committed
346
347
            raise EBNFCompilerError('Compiler must be run before calling '
                                    '"gen_transformer_Skeleton()"!')
348
349
        tt_name = self.grammar_name + '_AST_transformation_table'
        tf_name = self.grammar_name + 'Transform'
di68kap's avatar
di68kap committed
350
        transtable = [tt_name + ' = {',
351
352
                      '    # AST Transformations for the ' +
                      self.grammar_name + '-grammar']
353
        for name in self.rules:
354
355
            transtable.append('    "' + name + '": no_transformation,')
        transtable += ['    "*": no_transformation', '}', '', tf_name +
356
                       ' = partial(traverse, processing_table=%s)' % tt_name, '']
357
        transtable += [TRANSFORMER_FACTORY.format(NAME=self.grammar_name)]
358
359
        return '\n'.join(transtable)

360
    def gen_compiler_skeleton(self) -> str:
361
        if not self.rules:
362
363
            raise EBNFCompilerError('Compiler has not been run before calling '
                                    '"gen_Compiler_Skeleton()"!')
364
        compiler = ['class ' + self.grammar_name + 'Compiler(Compiler):',
365
366
367
368
                    '    """Compiler for the abstract-syntax-tree of a ' +
                    self.grammar_name + ' source file.',
                    '    """', '',
                    '    def __init__(self, grammar_name="' +
Eckhart Arnold's avatar
Eckhart Arnold committed
369
                    self.grammar_name + '", grammar_source=""):',
370
                    '        super(' + self.grammar_name +
Eckhart Arnold's avatar
Eckhart Arnold committed
371
                    'Compiler, self).__init__(grammar_name, grammar_source)',
372
                    "        assert re.match('\w+\Z', grammar_name)", '']
373
        for name in self.rules:
374
            method_name = Compiler.derive_method_name(name)
375
            if name == self.root:
376
                compiler += ['    def ' + method_name + '(self, node):',
377
378
                             '        return node', '']
            else:
379
                compiler += ['    def ' + method_name + '(self, node):',
380
                             '        pass', '']
381
        compiler += [COMPILER_FACTORY.format(NAME=self.grammar_name)]
382
        return '\n'.join(compiler)
383

384
    def assemble_parser(self, definitions: List[Tuple[str, str]], root_node: Node) -> str:
385
        # fix capture of variables that have been defined before usage [sic!]
386

387
388
389
        if self.variables:
            for i in range(len(definitions)):
                if definitions[i][0] in self.variables:
390
                    definitions[i] = (definitions[i][0], 'Capture(%s)' % definitions[i][1])
391

392
        definitions.append(('wspR__', self.WHITESPACE_KEYWORD
Eckhart Arnold's avatar
Eckhart Arnold committed
393
                            if 'right' in self.directives['literalws'] else "''"))
394
        definitions.append(('wspL__', self.WHITESPACE_KEYWORD
Eckhart Arnold's avatar
Eckhart Arnold committed
395
                            if 'left' in self.directives['literalws'] else "''"))
396
        definitions.append((self.WHITESPACE_KEYWORD,
397
398
399
400
401
402
403
                            ("mixin_comment(whitespace="
                             "r'{whitespace}', comment=r'{comment}')").
                            format(**self.directives)))
        definitions.append((self.COMMENT_KEYWORD, "r'{comment}'".format(**self.directives)))

        # prepare parser class header and docstring and
        # add EBNF grammar to the doc string of the parser class
404

405
        article = 'an ' if self.grammar_name[0:1] in "AaEeIiOoUu" else 'a '  # what about 'hour', 'universe' etc.?
406
        declarations = ['class ' + self.grammar_name +
407
                        'Grammar(Grammar):',
408
409
                        'r"""Parser for ' + article + self.grammar_name +
                        ' source file' +
410
                        (', with this grammar:' if self.grammar_source else '.')]
411
        definitions.append(('parser_initialization__', '"upon instatiation"'))
412
        if self.grammar_source:
413
            definitions.append(('source_hash__',
414
                                '"%s"' % md5(self.grammar_source, __version__)))
415
            declarations.append('')
416
            declarations += [line for line in self.grammar_source.split('\n')]
417
418
419
420
421
            while declarations[-1].strip() == '':
                declarations = declarations[:-1]
        declarations.append('"""')

        # turn definitions into declarations in reverse order
422

423
424
425
426
427
428
429
430
431
        self.root = definitions[0][0] if definitions else ""
        definitions.reverse()
        declarations += [symbol + ' = Forward()'
                         for symbol in sorted(list(self.recursive))]
        for symbol, statement in definitions:
            if symbol in self.recursive:
                declarations += [symbol + '.set(' + statement + ')']
            else:
                declarations += [symbol + ' = ' + statement]
432
433
434
435
436
437
438

        # check for symbols used but never defined

        defined_symbols = set(self.rules.keys()) | self.RESERVED_SYMBOLS
        for symbol in self.symbols:
            if symbol not in defined_symbols:
                self.symbols[symbol].add_error("Missing definition for symbol '%s'" % symbol)
439
                root_node.error_flag = True
440
441
442

        # check for unconnected rules

443
444
445
446
447
448
449
450
451
452
453
454
455
        if warnings():
            defined_symbols.difference_update(self.RESERVED_SYMBOLS)

            def remove_connections(symbol):
                if symbol in defined_symbols:
                    defined_symbols.remove(symbol)
                    for related in self.rules[symbol][1:]:
                        remove_connections(str(related))

            remove_connections(self.root)
            for leftover in defined_symbols:
                self.rules[leftover][0].add_error(('Rule "%s" is not connected to parser '
                                                   'root "%s"') % (leftover, self.root))
456
457
458

        # set root parser and assemble python grammar definition

459
        if self.root and 'root__' not in self.rules:
460
461
            declarations.append('root__ = ' + self.root)
        declarations.append('')
Eckhart Arnold's avatar
Eckhart Arnold committed
462
463
464
        self._result = '\n    '.join(declarations) \
                       + GRAMMAR_FACTORY.format(NAME=self.grammar_name)
        return self._result
465

466
    def on_syntax(self, node: Node) -> str:
467
468
469
470
        self._reset()
        definitions = []

        # drop the wrapping sequence node
471
472
        if len(node.children) == 1 and not node.children[0].parser.name:
            node = node.children[0]
473
474

        # compile definitions and directives and collect definitions
475
        for nd in node.children:
476
            if nd.parser.name == "definition":
477
                definitions.append(self._compile(nd))
478
479
            else:
                assert nd.parser.name == "directive", nd.as_sexpr()
480
                self._compile(nd)
481
                node.error_flag = node.error_flag or nd.error_flag
482

483
        return self.assemble_parser(definitions, node)
484

485
    def on_definition(self, node: Node) -> Tuple[str, str]:
486
        rule = str(node.children[0])
487
488
489
        if rule in self.rules:
            node.add_error('A rule with name "%s" has already been defined.' % rule)
        elif rule in EBNFCompiler.RESERVED_SYMBOLS:
490
491
492
493
            node.add_error('Symbol "%s" is a reserved symbol.' % rule)
        elif not sane_parser_name(rule):
            node.add_error('Illegal symbol "%s". Symbols must not start or '
                           ' end with a doube underscore "__".' % rule)
494
        elif rule in self.directives['tokens']:
495
496
497
498
            node.add_error('Symbol "%s" has already been defined as '
                           'a scanner token.' % rule)
        elif keyword.iskeyword(rule):
            node.add_error('Python keyword "%s" may not be used as a symbol. '
499
                           % rule + '(This may change in the future.)')
500
        try:
501
502
            self.current_symbols = [node]
            self.rules[rule] = self.current_symbols
503
            defn = self._compile(node.children[1])
504
            if rule in self.variables:
505
                defn = 'Capture(%s)' % defn
506
                self.variables.remove(rule)
507
508
509
            elif defn.find("(") < 0:
                # assume it's a synonym, like 'page = REGEX_PAGE_NR'
                defn = 'Synonym(%s)' % defn
510
511
512
513
        except TypeError as error:
            errmsg = EBNFCompiler.AST_ERROR + " (" + str(error) + ")\n" + node.as_sexpr()
            node.add_error(errmsg)
            rule, defn = rule + ':error', '"' + errmsg + '"'
Eckhart Arnold's avatar
Eckhart Arnold committed
514
        return rule, defn
515
516

    @staticmethod
517
    def _check_rx(node: Node, rx: str) -> str:
518
519
520
521
522
523
524
525
526
527
528
529
        """Checks whether the string `rx` represents a valid regular
        expression. Makes sure that multiline regular expressions are
        prepended by the multiline-flag. Returns the regular expression string.
        """
        rx = rx if rx.find('\n') < 0 or rx[0:4] == '(?x)' else '(?x)' + rx
        try:
            re.compile(rx)
        except Exception as re_error:
            node.add_error("malformed regular expression %s: %s" %
                           (repr(rx), str(re_error)))
        return rx

530
    def on_directive(self, node: Node) -> str:
531
        key = str(node.children[0]).lower()  # cast(str, node.children[0].result).lower()
532
        assert key not in self.directives['tokens']
533
        if key in {'comment', 'whitespace'}:
534
535
            if node.children[1].parser.name == "list_":
                if len(node.children[1].result) != 1:
Eckhart Arnold's avatar
Eckhart Arnold committed
536
                    node.add_error('Directive "%s" must have one, but not %i values.' %
537
538
                                   (key, len(node.children[1].result)))
                value = self._compile(node.children[1]).pop()
539
540
                if key == 'whitespace' and value in EBNFCompiler.WHITESPACE:
                    value = EBNFCompiler.WHITESPACE[value]  # replace whitespace-name by regex
541
                else:
542
                    node.add_error('Value "%s" not allowed for directive "%s".' % (value, key))
543
            else:
544
545
                value = str(node.children[1]).strip("~")  # cast(str, node.children[1].result).strip("~")
                if value != str(node.children[1]):  # cast(str, node.children[1].result):
546
547
548
549
550
551
                    node.add_error("Whitespace marker '~' not allowed in definition of "
                                   "%s regular expression." % key)
                if value[0] + value[-1] in {'""', "''"}:
                    value = escape_re(value[1:-1])
                elif value[0] + value[-1] == '//':
                    value = self._check_rx(node, value[1:-1])
552
553
554
                if key == 'whitespace' and not re.match(value, ''):
                    node.add_error("Implicit whitespace should always match the empty string, "
                                   "/%s/ does not." % value)
555
            self.directives[key] = value
556

557
        elif key == 'literalws':
558
            value = {item.lower() for item in self._compile(node.children[1])}
559
            if (len(value - {'left', 'right', 'both', 'none'}) > 0
Eckhart Arnold's avatar
Eckhart Arnold committed
560
                    or ('none' in value and len(value) > 1)):
561
562
563
564
565
566
567
                node.add_error('Directive "literalws" allows the values '
                               '`left`, `right`, `both` or `none`, '
                               'but not `%s`' % ", ".join(value))
            ws = {'left', 'right'} if 'both' in value \
                else {} if 'none' in value else value
            self.directives[key] = list(ws)

568
        elif key in {'tokens', 'scanner_tokens'}:
569
            self.directives['tokens'] |= self._compile(node.children[1])
570

571
        elif key.endswith('_filter'):
572
            filter_set = self._compile(node.children[1])
573
574
575
576
            if not isinstance(filter_set, set) or len(filter_set) != 1:
                node.add_error('Directive "%s" accepts exactly on symbol, not %s'
                               % (key, str(filter_set)))
            self.directives['filter'][key[:-7]] = filter_set.pop()
577

578
579
580
        else:
            node.add_error('Unknown directive %s ! (Known ones are %s .)' %
                           (key,
581
                            ', '.join(list(self.directives.keys()))))
582
583
        return ""

584
    def non_terminal(self, node: Node, parser_class: str, custom_args: List[str]=[]) -> str:
585
586
587
        """Compiles any non-terminal, where `parser_class` indicates the Parser class
        name for the particular non-terminal.
        """
588
        arguments = [self._compile(r) for r in node.children] + custom_args
589
590
        return parser_class + '(' + ', '.join(arguments) + ')'

591
    def on_expression(self, node) -> str:
592
593
        return self.non_terminal(node, 'Alternative')

594
    def on_term(self, node) -> str:
595
596
        return self.non_terminal(node, 'Sequence')

597
    def on_factor(self, node: Node) -> str:
598
        assert node.children
599
        assert len(node.children) >= 2, node.as_sexpr()
600
        prefix = str(node.children[0])  # cast(str, node.children[0].result)
601
        custom_args = []  # type: List[str]
602
603

        if prefix in {'::', ':'}:
604
605
            assert len(node.children) == 2
            arg = node.children[-1]
606
            if arg.parser.name != 'symbol':
Eckhart Arnold's avatar
Eckhart Arnold committed
607
                node.add_error(('Retrieve Operator "%s" requires a symbol, '
608
609
                                'and not a %s.') % (prefix, str(arg.parser)))
                return str(arg.result)
610
            if str(arg) in self.directives['filter']:
611
                custom_args = ['filter=%s' % self.directives['filter'][str(arg)]]
612
            self.variables.add(str(arg))  # cast(str, arg.result)
613

614
        elif len(node.children) > 2:
615
616
            # shift = (Node(node.parser, node.result[1].result),)
            # node.result[1].result = shift + node.result[2:]
617
618
619
620
            node.children[1].result = (Node(node.children[1].parser, node.children[1].result),) \
                                    + node.children[2:]
            node.children[1].parser = node.parser
            node.result = (node.children[0], node.children[1])
621

622
        node.result = node.children[1:]
623
624
625
626
627
        try:
            parser_class = self.PREFIX_TABLE[prefix]
            return self.non_terminal(node, parser_class, custom_args)
        except KeyError:
            node.add_error('Unknown prefix "%s".' % prefix)
628
        return ""
629

630
    def on_option(self, node) -> str:
631
632
        return self.non_terminal(node, 'Optional')

633
    def on_repetition(self, node) -> str:
634
635
        return self.non_terminal(node, 'ZeroOrMore')

636
    def on_oneormore(self, node) -> str:
637
638
        return self.non_terminal(node, 'OneOrMore')

639
    def on_regexchain(self, node) -> str:
640
641
        raise EBNFCompilerError("Not yet implemented!")

642
    def on_group(self, node) -> str:
643
644
645
        raise EBNFCompilerError("Group nodes should have been eliminated by "
                                "AST transformation!")

646
647
648
649
    def on_symbol(self, node: Node) -> str:     # called only for symbols on the right hand side!
        symbol = str(node)  # ; assert result == cast(str, node.result)
        if symbol in self.directives['tokens']:
            return 'ScannerToken("' + symbol + '")'
650
        else:
651
652
653
654
655
656
            self.current_symbols.append(node)
            if symbol not in self.symbols:
                self.symbols[symbol] = node
            if symbol in self.rules:
                self.recursive.add(symbol)
            return symbol
657

658
    def on_literal(self, node) -> str:
659
        return 'Token(' + str(node).replace('\\', r'\\') + ')'  # return 'Token(' + ', '.join([node.result]) + ')' ?
660

661
    def on_regexp(self, node: Node) -> str:
662
        rx = str(node)
663
        name = []   # type: List[str]
664
665
        if rx[:2] == '~/':
            if not 'left' in self.directives['literalws']:
666
                name = ['wL=' + self.WHITESPACE_KEYWORD] + name
667
668
669
670
            rx = rx[1:]
        elif 'left' in self.directives['literalws']:
            name = ["wL=''"] + name
        if rx[-2:] == '/~':
Eckhart Arnold's avatar
Eckhart Arnold committed
671
            if 'right' not in self.directives['literalws']:
672
                name = ['wR=' + self.WHITESPACE_KEYWORD] + name
673
674
675
676
677
678
679
680
681
682
683
684
            rx = rx[:-1]
        elif 'right' in self.directives['literalws']:
            name = ["wR=''"] + name
        try:
            arg = repr(self._check_rx(node, rx[1:-1].replace(r'\/', '/')))
        except AttributeError as error:
            errmsg = EBNFCompiler.AST_ERROR + " (" + str(error) + ")\n" + \
                     node.as_sexpr()
            node.add_error(errmsg)
            return '"' + errmsg + '"'
        return 'RE(' + ', '.join([arg] + name) + ')'

685
    def on_list_(self, node) -> Set[str]:
686
        assert node.children
687
        return set(item.result.strip() for item in node.children)
688
689


690
def get_ebnf_compiler(grammar_name="", grammar_source="") -> EBNFCompiler:
Eckhart Arnold's avatar
Eckhart Arnold committed
691
692
693
694
695
696
697
698
    global thread_local_ebnf_compiler_singleton
    try:
        compiler = thread_local_ebnf_compiler_singleton
        compiler.set_grammar_name(grammar_name, grammar_source)
        return compiler
    except NameError:
        thread_local_ebnf_compiler_singleton = EBNFCompiler(grammar_name, grammar_source)
        return thread_local_ebnf_compiler_singleton