def test_lookahead(self):
grammar = Grammar(r'''starts_with_a = &"a" ~"[a-z]+"''')
self.assertRaises(ParseError, grammar.parse, 'burp')
s = 'arp'
self.assertEqual(grammar.parse('arp'), Node(grammar['starts_with_a'], s, 0, 3, children=[
Node(Lookahead(Literal('a')), s, 0, 0),
Node(Regex(r'[a-z]+'), s, 0, 3)]))
def visit_lookahead_term(self, node, lookahead_term):
ampersand, term, _ = lookahead_term
return Lookahead(term)
"""Treat a parenthesized subexpression as just its contents.
Its position in the tree suffices to maintain its grouping semantics.
"""
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)):
def visit_lookahead_term(self, lookahead_term, xxx_todo_changeme3):
(ampersand, term, _) = xxx_todo_changeme3
return Lookahead(term)
def visit_lookahead_term(self, lookahead_term, children):
return Lookahead(children[1])
