/*

Exercise 1: Functional programming using delegates and generics
===============================================================

Exercise 1.1 (mandatory) Construct a generic method Forall that takes an array of type T and a predicate on
T and returns a boolean. Method Forall should return true if the predicate holds for all elements in the array.
Construct a Main method to test Forall. This should call Forall with a list of integers and the even predicate
testing if an integer is even.

Test also Forall on an array of arrays of integers with a predicate that tests if an
array has more than 2 elements.

Declare a method Exists with the same signature as Forall, but which returns true if there exists some
element in the array for which the predicate is true. Test your method.

*/
using System;

namespace exercise_5
{
    public class Exercise_5_1_1
    {

        // note: just dont do Forall(.. generics requires Forall<T>(..
        public static bool Forall<T>(T[] xs, Func<T, bool> p) {

            foreach(T x in xs) {
                if (!(p(x))) return false;
            }

            return true;
        }


        public static bool Exists<T>(T[] xs, Func<T, bool> p) {

            foreach(T x in xs) {
                if ((p(x))) return true;
            }

            return false;
        }


        public static void Main() {

            Console.WriteLine("create an array from 0 to 9");

            int[] a = {0,1,2,3,4,5,6,7,8,9};

            Console.WriteLine("check if the array only contains even numbers");

            Console.WriteLine(Forall(a, x => x % 2 == 0)); // expected false

            Console.WriteLine("check if the array only contains odd numbers");

            Console.WriteLine(Forall(a, x => x % 2 != 0)); // expected false


            Console.WriteLine("create an array from 0 to 8 - only with even numbers");

            int[] evenNumbers = {0,2,4,6,8};

            Console.WriteLine("check if the array only contains even numbers");

            Console.WriteLine(Forall(evenNumbers, x => x % 2 == 0)); // expected true

            Console.WriteLine("check if the array only contains odd numbers");

            Console.WriteLine(Forall(evenNumbers, x => x % 2 != 0)); // expected false


            Console.WriteLine("create an array from 1 to 9 - only with odd numbers");

            int[] oddNumbers = {1,3,5,7,9};

            Console.WriteLine("check if the array only contains even numbers");

            Console.WriteLine(Forall(oddNumbers, x => x % 2 == 0)); // expected false

            Console.WriteLine("check if the array only contains odd numbers");

            Console.WriteLine(Forall(oddNumbers, x => x % 2 != 0)); // expected true

            Console.WriteLine("test the arrays in arrays - create one array also containg an array of =< 2 elements and another array nly containing arrays > 2 elements");

            int[] smallA = {1};
            int[] smallA2 = {1,2};
            int[][] multiple = {a, evenNumbers, oddNumbers, smallA, smallA2};
            int[][] multiple2 = {a, evenNumbers, oddNumbers};

            Console.WriteLine(Forall(multiple, x => x.Length > 2)); // expected false

            Console.WriteLine(Forall(multiple2, x => x.Length > 2)); // expected true

            Console.WriteLine("test the Exists() ");

            Console.WriteLine(Exists(oddNumbers, x => x == 9)); // expected true

            Console.WriteLine(Exists(oddNumbers, x => x == 0)); // expected false


            Console.WriteLine("test the Exists() with an array of strings");

            string[] s = {"c#", "java", "python", "lisp"};

            Console.WriteLine(Exists(s, x => x.Equals("python"))); // expected true

            Console.WriteLine(Exists(oddNumbers, x => x.Equals("perl"))); // expected false

        }

    }
}