def testTrailingLookahead(self):
"""Lookahead at the end of a production is banned."""
tokenize = lexer.LexicalGrammar('IF ( X ) ELSE OTHER ;')
grammar = gen.Grammar({
'goal': [['stmt']],
'stmt': [
['OTHER', ';'],
[
'IF', '(', 'X', ')', 'stmt',
LookaheadRule(frozenset({'ELSE'}), False)
],
['IF', '(', 'X', ')', 'stmt', 'ELSE', 'stmt'],
],
})
def stmt_0():
return ('stmt_0', 'OTHER', ';')
def stmt_1(t):
return ('stmt_1', 'IF', '(', 'X', ')', t)
def stmt_2(t, e):
return ('stmt_2', 'IF', '(', 'X', ')', t, 'ELSE', e)
self.compile(tokenize, grammar)
self.assertParse('IF(X) OTHER;', stmt_1(stmt_0()))
self.assertParse('IF(X) OTHER; ELSE OTHER;',
stmt_2(stmt_0(), stmt_0()))
self.assertParse('IF(X) IF(X) OTHER; ELSE OTHER; ELSE OTHER;',
stmt_2(stmt_2(stmt_0(), stmt_0()), stmt_0()))
self.assertParse('IF(X) OTHER; ELSE IF(X) OTHER; ELSE OTHER;',
stmt_2(stmt_0(), stmt_2(stmt_0(), stmt_0())))
self.assertParse('IF(X) IF(X) OTHER; ELSE OTHER;',
stmt_1(stmt_2(stmt_0(), stmt_0())))
def testTrailingLookahead(self):
"""Lookahead at the end of a production is banned."""
grammar = gen.Grammar({
'stmt': [
['OTHER', ';'],
['IF', '(', 'X', ')', 'stmt',
LookaheadRule(frozenset({'ELSE'}), False)],
['IF', '(', 'X', ')', 'stmt', 'ELSE', 'stmt'],
],
})
self.assertRaisesRegex(
ValueError,
r"invalid grammar: lookahead restriction at end of production",
lambda: gen.compile(grammar))