def test_prefer_shifts_no_sr_conflicts():
"""
Test that grammar with S/R conflict will be resolved to SHIFT actions
if prefer_shift option is used.
"""
# This grammar has S/R conflict as B+ may consume multiple single "a" A
# because "b" is optional. Thus, parser can't decide if it should shift "a"
# or reduce by 'B: "b"? A+' and later by 'S: B+'; Most of the time we want
# gready behavior so in case of doubt parser will choose shift if
# prefer_shift is set to `True`. This means that the parser will first
# consume all "a" using A+ and that reduce B at the end.
grammar = r"""
S: B+;
B: "b"? A+;
terminals
A: "a";
"""
g = Grammar.from_string(grammar)
# There is a shift reduce conflict so we can't use LR parser.
table = create_table(g)
assert len(table.sr_conflicts) == 1
# But we can eliminate conflict by prefer_shifts strategy.
table = create_table(g, prefer_shifts=True)
assert len(table.sr_conflicts) == 0
# With prefer_shifts we get a greedy behavior
input_str = 'b a a a b a a'
output = [['b', ['a', 'a', 'a']], ['b', ['a', 'a']]]
parser = Parser(g, prefer_shifts=True)
result = parser.parse(input_str)
assert result == output
# GLR parser can parse without prefer_shifts strategy. This grammar is
# ambiguous and yields 8 solutions for the given input.
parser = GLRParser(g)
results = [parser.call_actions(tree) for tree in parser.parse(input_str)]
expected = [[['b', ['a']], [None, ['a']], [None, ['a']], ['b', ['a']],
[None, ['a']]],
[['b', ['a', 'a']], [None, ['a']], ['b', ['a']], [None,
['a']]],
[['b', ['a']], [None, ['a', 'a']], ['b', ['a']], [None,
['a']]],
[['b', ['a', 'a', 'a']], ['b', ['a']], [None, ['a']]],
[['b', ['a']], [None, ['a']], [None, ['a']], ['b', ['a',
'a']]],
[['b', ['a', 'a']], [None, ['a']], ['b', ['a', 'a']]],
[['b', ['a']], [None, ['a', 'a']], ['b', ['a', 'a']]],
[['b', ['a', 'a', 'a']], ['b', ['a', 'a']]]]
assert results == expected
# But if `prefer_shift` is used we get only one solution
parser = GLRParser(g, prefer_shifts=True)
result = parser.parse(input_str)
assert len(result) == 1
assert parser.call_actions(result[0]) == output
def test_parse_context_call_actions():
"""
Test that valid context attributes are available when calling
actions using `call_actions`.
"""
global called
called = [False, False]
actions["E"][0] = act_sum(is_tree=True)
parser = Parser(g, build_tree=True, actions=actions)
tree = parser.parse(" 1 + 2 ")
parser.call_actions(tree)
assert all(called)
def test_action_override():
"""
Explicitely provided action in `actions` param overrides default or
grammar provided.
"""
grammar = """
S: Foo Bar;
@pass_nochange
Bar: "1" a;
terminals
@pass_nochange
Foo: 'foo';
a: "a";
"""
g = Grammar.from_string(grammar)
p = Parser(g)
input_str = "foo 1 a"
result = p.parse(input_str)
assert result == ["foo", ["1", "a"]]
actions = {"Foo": lambda _, __: "eggs", "Bar": lambda _, __: "bar reduce"}
p = Parser(g, actions=actions)
result = p.parse(input_str)
assert result == ["eggs", "bar reduce"]
# Test with actions call postponing
p = Parser(g, build_tree=True, actions=actions)
tree = p.parse(input_str)
result = p.call_actions(tree)
assert result == ["eggs", "bar reduce"]
def test_parse_context_call_actions():
"""
Test that valid context attributes are available when calling
actions using `call_actions`.
"""
global called
called = [False, False, False]
parser = Parser(g, build_tree=True, actions=actions, debug=True)
tree = parser.parse(" 1 + 2 ")
context = Context()
context.call_actions = True
parser.call_actions(tree, context=context)
assert all(called)
assert node_exists[0]
def test_actions_manual():
"""
Actions may be called as a separate step.
"""
grammar = get_grammar()
p = Parser(grammar, build_tree=True, actions=get_actions())
result = p.parse("""34.7+78*34 +89+
12.223*4""")
assert type(result) is NodeNonTerm
assert p.call_actions(result) == \
34.7 + 78 * 34 + 89 + 12.223 * 4
