public void TupleTest()
{
bool isExecuted = false;
ValueTuple <int> one = new ValueTuple <int>(1);
ValueTuple <int> two = new ValueTuple <int>(2);
Func <int, Func <int, int> > add = x => y => { isExecuted = true; return(x + y); };
ValueTuple <int> query = from x in one
from y in two
from _ in one
select add(x)(y);
Assert.IsTrue(isExecuted); // Immediate execution.
Assert.AreEqual(1 + 2, query.Item1); // Execution.
// Monad law 1: m.Monad().SelectMany(f) == f(m)
Func <int, ValueTuple <int> > addOne = x => (x + 1).ValueTuple();
ValueTuple <int> left = 1.ValueTuple().SelectMany(addOne, False);
ValueTuple <int> right = addOne(1);
Assert.AreEqual(left.Item1, right.Item1);
// Monad law 2: M.SelectMany(Monad) == M
ValueTuple <int> M = 1.ValueTuple();
left = M.SelectMany(ValueTupleExtensions.ValueTuple, False);
right = M;
Assert.AreEqual(left.Item1, right.Item1);
// Monad law 3: M.SelectMany(f1).SelectMany(f2) == M.SelectMany(x => f1(x).SelectMany(f2))
Func <int, ValueTuple <int> > addTwo = x => (x + 2).ValueTuple();
left = M.SelectMany(addOne, False).SelectMany(addTwo, False);
right = M.SelectMany(x => addOne(x).SelectMany(addTwo, False), False);
Assert.AreEqual(left.Item1, right.Item1);
}