from btl_syntax import *    # using all of the module on purpose
import btl_interpreter

def test_constructor():
    sample = Pred(If(IsZero(Zero()),
                     Succ(Succ(Zero())),
                     Zero()))
    assert(sample.to_string()
            == "Pred(If(IsZero(Zero), Succ(Succ(Zero)), Zero))")
    sample = If(IsZero(Zero()),
                Succ(Succ(Zero())),
                Zero())
    assert(sample.to_string()
           == "If(IsZero(Zero), Succ(Succ(Zero)), Zero)")

def test_number_interpretation():
    x = Succ(Succ(Succ(Zero())))
    assert(btl_interpreter.eval(x) == 3)
    x = Pred(Succ(Succ(Zero())))
    assert(btl_interpreter.eval(x) == 1)
    x = If(IsZero(Zero()), Succ(Succ(Zero())), Zero())
    assert(btl_interpreter.eval(x) == 2)
    x = If(IsZero(Succ(Zero())), Succ(Succ(Zero())), Zero())
    assert(btl_interpreter.eval(x) == 0)
    x = Pred(Pred(Zero()))
    assert(btl_interpreter.eval(x) == 0)

test_constructor()
test_number_interpretation()
print("all tests pass")