def eval(self, environment):
if trueExpr(self._test.eval(environment)):
return self._cons.eval(environment)
else:
if self._alt:
return self._alt.eval(environment)
else:
return None
def eval(self, environment):
if not self._tests:
return FALSE
for test in self._tests[:-1]:
value = test.eval(environment)
if trueExpr(value):
return value
return self._tests[-1].eval(environment)
def evalTest(self, environment):
"""Evaluates the test and returns true if the test evaluates
to true.
"""
return trueExpr(self._test.eval(environment))