gistfile1.py

def vau(ptree, env):
	t1, s, t2 = ptree
	fv = set.union(
		t2.free_variables(),
		env.free_variables())
	if s is Ignore:
		c, env1, _ = definiend(t1, fv)
		return c.subst(evaluate(t2, concat_envs(env1, env)))
	else:
		x, X = make_distinct_var(fv)
		c, env1, _ = definiend(t1, X)
		new_env = concat_envs(env1, Environment({ s: x }), env)
		return Epsilon(UnaryOperative(c.subst(
			evaluate(t2, new_env))))