static RecursionResult <BigInteger> Factorial(int n, BigInteger product)
{
if (n < 2)
{
return(TailRecursion.Return(product));
}
return(TailRecursion.Next(() => Factorial(n - 1, n * product)));
}
public void Factorial_should_return_same_result_for_all_implementations(int n)
{
var basicResult = BasicRecursion.Factorial(n);
var tailResult = TailRecursion.Factorial(n);
var iterrativeResult = Iterative.Factorial(n);
var enumerableResult = Enumerable.Factorial(n);
Assert.That(basicResult, Is.EqualTo(tailResult));
Assert.That(basicResult, Is.EqualTo(iterrativeResult));
Assert.That(basicResult, Is.EqualTo(enumerableResult));
}
public void Returns_final_result_after_recursion()
{
RecursionResult <int> Factorial(int k)
{
RecursionResult <int> FactorialAcc(int m, int acc)
{
if (m == 1)
{
return(RecursionResult <int> .Final(acc));
}
return(RecursionResult <int> .Next(() => FactorialAcc(m - 1, m *acc)));
}
return(FactorialAcc(k, 1));
}
Assert.Equal(5 * 4 * 3 * 2 * 1, TailRecursion.Run(() => Factorial(5)));
}
public void Deep_recursion_does_not_blow_the_stack()
{
RecursionResult <BigInteger> Factorial(int k)
{
RecursionResult <BigInteger> FactorialAcc(int m, BigInteger acc)
{
if (m == 1)
{
return(RecursionResult <BigInteger> .Final(acc));
}
return(RecursionResult <BigInteger> .Next(() => FactorialAcc(m - 1, m *acc)));
}
return(FactorialAcc(k, 1));
}
var ex = Record.Exception(() => TailRecursion.Run(() => Factorial(20000)));
Assert.Null(ex);
}
static void Main(string[] args)
{
BigInteger result = TailRecursion.Execute(() => Factorial(50000, 1));
}
public int TailRecursionTest()
{
return(TailRecursion.Factorial(N));
}
public BigInteger FactorialTrampoline(int x)
{
BigInteger result = TailRecursion.Execute(() => Factorial(x, 1));
return(result);
}
public void Returns_final_result()
{
RecursionResult <int> F() => RecursionResult <int> .Final(1);
Assert.Equal(1, TailRecursion.Run(F));
}
public void Returns_final_result_from_next_iteration()
{
RecursionResult <int> F() => RecursionResult <int> .Next(() => RecursionResult <int> .Final(2));
Assert.Equal(2, TailRecursion.Run(F));
}
