def occur_check(var, obj):
"""Return true if var occurs anywhere in obj."""
if var == obj:
return True
elif isinstance(obj, Expr):
return var.op == obj.op or occur_check(var, obj.args)
elif not isterm(obj) and utils.is_sequence(obj):
for xi in obj:
if occur_check(var, xi):
return True
return False
def occur_check(var, obj):
"""Return true if var occurs anywhere in obj."""
if var == obj:
return True
elif isinstance(obj, Expr):
return var.op == obj.op or occur_check(var, obj.args)
elif not isterm(obj) and utils.is_sequence(obj):
for xi in obj:
if occur_check(var, xi):
return True
return False
def unify(x, y, s):
"""Unify expressions x,y with substitution s; return a substitution that
would make x,y equal, or None if x,y can not unify. x and y can be
variables (e.g. Expr('x')), constants, lists, or Exprs. [Fig. 9.1]
>>> unify(x + y, y + C, {})
{y: C, x: y}
"""
if s is None:
return None
elif x == y:
return s
elif is_variable(x):
return unify_var(x, y, s)
elif is_variable(y):
return unify_var(y, x, s)
elif isinstance(x, Expr) and isinstance(y, Expr):
return unify(x.args, y.args, unify(x.op, y.op, s))
elif isterm(x) or isterm(y) or not x or not y:
return utils.if_(x == y, s, None)
elif utils.is_sequence(x) and utils.is_sequence(y) and len(x) == len(y):
return unify(x[1:], y[1:], unify(x[0], y[0], s))
else:
return None
def unify(x, y, s):
"""Unify expressions x,y with substitution s; return a substitution that
would make x,y equal, or None if x,y can not unify. x and y can be
variables (e.g. Expr('x')), constants, lists, or Exprs. [Fig. 9.1]
>>> unify(x + y, y + C, {})
{y: C, x: y}
"""
if s is None:
return None
elif x == y:
return s
elif is_variable(x):
return unify_var(x, y, s)
elif is_variable(y):
return unify_var(y, x, s)
elif isinstance(x, Expr) and isinstance(y, Expr):
return unify(x.args, y.args, unify(x.op, y.op, s))
elif isterm(x) or isterm(y) or not x or not y:
return utils.if_(x == y, s, None)
elif utils.is_sequence(x) and utils.is_sequence(y) and len(x) == len(y):
return unify(x[1:], y[1:], unify(x[0], y[0], s))
else:
return None
def test_is_sequence(self):
"""Test is_sequence."""
self.assertTrue(utils.is_sequence({}))
self.assertTrue(utils.is_sequence([]))
self.assertFalse(utils.is_sequence(5))
self.assertFalse(utils.is_sequence(self))
def test_is_sequence(self):
"""Test is_sequence."""
self.assertTrue(utils.is_sequence({}))
self.assertTrue(utils.is_sequence([]))
self.assertFalse(utils.is_sequence(5))
self.assertFalse(utils.is_sequence(self))
