def _expressions_from_rules(self, rule_syntax, custom_rules):
"""Return the rules for parsing the grammar definition syntax.
Return a 2-tuple: a dict of rule names pointing to their expressions,
and then the top-level expression for the first rule.
"""
# 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('[ilmsuxa]*', 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)
def visit_not_term(self, node, not_term):
exclamation, term, _ = not_term
return Not(term)
def test_not(self):
len_eq(Not(Regex('.')).match(''), 0) # match
assert_raises(ParseError, Not(Regex('.')).match, 'Hi') # don't
"""
return expression
def visit_quantifier(self, quantifier, (symbol, _)):
"""Turn a quantifier into just its symbol-matching node."""
return symbol
def visit_quantified(self, quantified, (atom, quantifier)):
return self.quantifier_classes[quantifier.text](atom)
def visit_lookahead_term(self, lookahead_term, (ampersand, term, _)):
return Lookahead(term)
def visit_not_term(self, not_term, (exclamation, term, _)):
return Not(term)
def visit_rule(self, rule, (label, equals, expression)):
"""Assign a name to the Expression and return it."""
expression.name = label # Assign a name to the expr.
return expression
def visit_sequence(self, sequence, (term, other_terms)):
"""A parsed Sequence looks like [term node, OneOrMore node of
``another_term``s]. Flatten it out."""
return Sequence(term, *other_terms)
def visit_ored(self, ored, (first_term, other_terms)):
return OneOf(first_term, *other_terms)
def visit_or_term(self, or_term, (slash, _, term)):
def visit_not_term(self, not_term, xxx_todo_changeme4):
(exclamation, term, _) = xxx_todo_changeme4
return Not(term)
def visit_not_term(self, not_term, children):
return Not(children[1])
def test_not(self):
len_eq(Not(Regex('.')).match(''), 0) # match
len_eq(Not(Regex('.')).match('Hi'), None) # don't
