import fol


def test_empty_subst():
    root = fol.parse('Happy(x)').subst({})
    assert 'PRED[Happy](VAR[x])' == str(root)


def test_one_var_subst():
    root = fol.parse('Happy(x)').subst({'x': fol.term('z')})
    assert 'PRED[Happy](VAR[z])' == str(root)


def test_one_function_subst():
    root = fol.parse('Happy(x)').subst({'x': fol.term('f(z)')})
    assert 'PRED[Happy](FUN[f](VAR[z]))' == str(root)


def test_ambiguous_subst():
    root = fol.parse('Happy(x)').subst({
        'x': fol.term('y'),
        'y': fol.term('z'),
    })
    assert 'PRED[Happy](VAR[y])' == str(root)


def test_ambiguous_reverse_subst():
    root = fol.parse('Happy(x, y)').subst({
        'y': fol.term('z'),
        'x': fol.term('y'),
    })
    assert 'PRED[Happy](VAR[y],VAR[z])' == str(root)