def _expressions_from_rules(self, rule_syntax, custom_rules):
        # Hard-code enough of the rules to parse the grammar that describes the
        # grammar description language, to bootstrap:
        comment = Regex(r'#[^\r\n]*', name='comment')
        meaninglessness = OneOf(Regex(r'\s+'), comment, name='meaninglessness')
        _ = ZeroOrMore(meaninglessness, name='_')
        equals = Sequence(Literal('='), _, name='equals')
        label = Sequence(Regex(r'[a-zA-Z_][a-zA-Z_0-9]*'), _, name='label')
        reference = Sequence(label, Not(equals), name='reference')
        quantifier = Sequence(Regex(r'[*+?]'), _, name='quantifier')
        # This pattern supports empty literals. TODO: A problem?
        spaceless_literal = Regex(r'u?r?"[^"\\]*(?:\\.[^"\\]*)*"',
                                  ignore_case=True,
                                  dot_all=True,
                                  name='spaceless_literal')
        literal = Sequence(spaceless_literal, _, name='literal')
        regex = Sequence(Literal('~'),
                         literal,
                         Regex('[ilmsux]*', ignore_case=True),
                         _,
                         name='regex')
        atom = OneOf(reference, literal, regex, name='atom')
        quantified = Sequence(atom, quantifier, name='quantified')

        term = OneOf(quantified, atom, name='term')
        not_term = Sequence(Literal('!'), term, _, name='not_term')
        term.members = (not_term,) + term.members

        sequence = Sequence(term, OneOrMore(term), name='sequence')
        or_term = Sequence(Literal('/'), _, term, name='or_term')
        ored = Sequence(term, OneOrMore(or_term), name='ored')
        expression = OneOf(ored, sequence, term, name='expression')
        rule = Sequence(label, equals, expression, name='rule')
        rules = Sequence(_, OneOrMore(rule), name='rules')

        # Use those hard-coded rules to parse the (more extensive) rule syntax.
        # (For example, unless I start using parentheses in the rule language
        # definition itself, I should never have to hard-code expressions for
        # those above.)

        rule_tree = rules.parse(rule_syntax)

        # Turn the parse tree into a map of expressions:
        return RuleVisitor().visit(rule_tree)


# The grammar for parsing PEG grammar definitions:
# This is a nice, simple grammar. We may someday add to it, but it's a safe bet
# that the future will always be a superset of this.
Packs and writes structure into stream
dataset/ETHPy150Open erikrose/parsimonious/parsimonious/grammar.py/BootstrappingGrammar._expressions_from_rules--crossover with--dataset/ETHPy150Open denisenkom/pytds/pytds/tds.py/_TdsWriter.pack