functional-programming.cs

using System;
using FunctionalProgramming;

namespace FunctionalProgramming
{
    public interface IOperation<I, O>
    {
        O Apply(I arg);
    }

    public class Operator<A, B, O>
    {
        private Func<A, B, O> func;

        public Operator(Func<A, B, O> func)
        {
            this.func = func;
        }

        public static OperatorLeftArg<A, B, O> operator |(A arg, Operator<A, B, O> op)
        {
            return new OperatorLeftArg<A, B, O>(op.func, arg);
        }

        public static OperatorRightArg<A, B, O> operator |(Operator<A, B, O> op, B arg)
        {
            return new OperatorRightArg<A, B, O>(op.func, arg);
        }
    }

    public class OperatorLeftArg<A, B, O> : IOperation<B, O>
    {
        private Func<A, B, O> func;
        private A arg;

        public OperatorLeftArg(Func<A, B, O> func, A arg)
        {
            this.func = func;
            this.arg = arg;
        }

        public static O operator |(OperatorLeftArg<A, B, O> op, B arg)
        {
            return op.func(op.arg, arg);
        }

        public O Apply(B arg)
        {
            return this | arg;
        }
    }

    public class OperatorRightArg<A, B, O> : IOperation<A, O>
    {
        private Func<A, B, O> func;
        private B arg;

        public OperatorRightArg(Func<A, B, O> func, B arg)
        {
            this.func = func;
            this.arg = arg;
        }

        public O Apply(A arg)
        {
            return this.func(arg, this.arg);
        }
    }
}

namespace FPinCSh
{
    class Program
    {
        static void Main(string[] args)
        {
            var plus = new Operator<int, int, int>((a, b) => a + b);
            var times = new Operator<int, int, int>((a, b) => a * b);
            var pow = new Operator<double, double, double>(Math.Pow);
            var square = pow | 2;
            var twopower = 2 | pow;
            Console.WriteLine("4 `plus` (3 `times` 2) = {0}", 4 | plus | (3 | times | 2));
            Console.WriteLine("square 3 = {0}", square.Apply(3.0));
            Console.WriteLine("twopower 3 = {0}", twopower.Apply(3.0));
            Console.ReadKey(true);
        }
    }
}