Top level.

terribleTest.java

    @Test
    public void test() {
        Environment env = new Environment();

        env.register(assign($("a"), plus($("b"), $("c"))));
        env.register(assign($("c"), multiply($(2), $("d"))));
        env.register(assign($("b"), $(3)));
        env.register(assign($("d"), $(2)));

        Assert.assertThat(env.valueOf($("a")), equalTo(7));
        Assert.assertThat(env.valueOf($("b")), equalTo(3));
        Assert.assertThat(env.valueOf($("c")), equalTo(4));
        Assert.assertThat(env.valueOf($("d")), equalTo(2));
    }