def test__get_derivations__3(self):
p = Program.parse("""
a <- b, c.
b <- d, e.
b <- c.
c <- f, g.
d <- h.
e.
f.
g.
h.
""")
i = Interpreter(p)
expected = {
Derivation([
Rule.parse('b <- c.'),
Rule.parse('c <- f, g.'),
Rule.parse('f.'),
Rule.parse('g.')
], i),
Derivation([
Rule.parse('b <- d, e.'),
Rule.parse('d <- h.'),
Rule.parse('h.'),
Rule.parse('e.')
], i),
}
result = i.get_derivations(Literal.parse('b'))
assert_that(result).is_equal_to(expected)
def test__get_derivations__flies_tina__defeasibly(self):
p = Program.parse("""
bird(X) <- chicken(X).
bird(X) <- penguin(X).
~flies(X) <- penguin(X).
chicken(tina).
penguin(tweety).
scared(tina).
flies(X) -< bird(X).
flies(X) -< chicken(X), scared(X).
nests_in_trees(X) -< flies(X).
~flies(X) -< chicken(X).
""")
i = Interpreter(p)
expected = {
Derivation([
Rule.parse('flies(tina) -< chicken(tina), scared(tina).'),
Rule.parse('chicken(tina).'),
Rule.parse('scared(tina).')
], i),
Derivation([
Rule.parse('flies(tina) -< bird(tina).'),
Rule.parse('bird(tina) <- chicken(tina).'),
Rule.parse('chicken(tina).')
], i),
}
result = i.get_derivations(Literal.parse('flies(tina)'),
RuleType.DEFEASIBLE)
assert_that(result).is_equal_to(expected)
def test__get_derivations__not_flies_tina__strictly(self):
p = Program.parse("""
bird(X) <- chicken(X).
bird(X) <- penguin(X).
~flies(X) <- penguin(X).
chicken(tina).
penguin(tweety).
scared(tina).
flies(X) -< bird(X).
flies(X) -< chicken(X), scared(X).
nests_in_trees(X) -< flies(X).
~flies(X) -< chicken(X).
""")
i = Interpreter(p)
expected = set()
result = i.get_derivations(Literal.parse('~flies(tina)'),
RuleType.STRICT)
assert_that(result).is_equal_to(expected)