C # functional programming style-Implementation of Fan Filter, Map, and CT Functions

In the morning, I read an article about lambda and closure from yuanyou, and suddenly I think of Python I just learned. I was so happy when I first came into contact with FP. The yearning for the no-side-effect of FP and my love for Declaration-type programming have led me to a change in programming and another idea of programming.

I still remember seeing the built-in function Filter, Map, and Reduce in Python, wondering why. NET's BCL didn't exist. After C #3.0 is released, you can basically DIY a cottage Filter, Map, and Reduce. Check the Code:

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace FuncPro{    class Program    {        static T[] Filter<T>(Func<T, bool> func, IEnumerable<T> iSource)        {            List<T> iResult = new List<T>();            foreach (var item in iSource)            {                if (func(item))                    iResult.Add(item);            }            return iResult.ToArray();        }        static T[] Map<T>(Func<T, T> func, IEnumerable<T> iSource)        {            List<T> iResult = new List<T>();            foreach (var item in iSource)            {                iResult.Add(func(item));            }            return iResult.ToArray();        }        static T Reduce<T>(Func<T, T, T> func, IEnumerable<T> iSource)        {            T sum = default(T);            foreach (var item in iSource)            {                sum = func(sum, item);            }            return sum;        }        static void PrintArray(int[] iSource)        {            Console.Write("\t");            iSource.ToList().ForEach(x => Console.Write("{0} ", x));            Console.WriteLine();        }        static void Indent(string msg)        {            Console.WriteLine("{0}:", msg);        }        static void Main(string[] args)        {            int[] iSource = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };            Indent("Source");            PrintArray(iSource);                        int[] iFilterResult = Filter(x => x > 5, iSource);            Indent("Filter, item more than 5");            PrintArray(iFilterResult);            int[] iMapResult = Map(x => x * 2, iSource);            Indent("Map, multiple with 2");            PrintArray(iMapResult);            int iReduceResult = Reduce((x, y) => x + y, iSource);            Indent("Reduce");            Console.Write("\t{0}\n ", iReduceResult);            Console.ReadKey();        }    }}

Chatting with a friend a few days ago. NET has added many functional programming elements and should be able to write functional programming-style code. It should also be a language that supports functional programming, today, I am writing the code.

PS.

Today, when I read "CLR via C # 3e", I saw an example of how Jefferey improved code readability by using the Extension Method. I reconstructed the above Code to improve readability:

static class ExtendMethod{    public static void ShowItems<T>(this IEnumerable<T> collection)    {        Console.Write("\t");        collection.ToList().ForEach((x) => Console.Write("{0} ", x));        Console.WriteLine();    }}class Program{    static T[] Filter<T>(Func<T, bool> func, IEnumerable<T> iSource)    {        List<T> iResult = new List<T>();        foreach (var item in iSource)        {            if (func(item))                iResult.Add(item);        }        return iResult.ToArray();    }    static T[] Map<T>(Func<T, T> func, IEnumerable<T> iSource)    {        List<T> iResult = new List<T>();        foreach (var item in iSource)        {            iResult.Add(func(item));        }        return iResult.ToArray();    }    static T Reduce<T>(Func<T, T, T> func, IEnumerable<T> iSource)    {        T sum = default(T);        foreach (var item in iSource)        {            sum = func(sum, item);        }        return sum;    }    static void PrintArray(int[] iSource)    {        Console.Write("\t");        iSource.ToList().ForEach(x => Console.Write("{0} ", x));        Console.WriteLine();    }    static void Indent(string msg)    {        Console.WriteLine("{0}:", msg);    }    static void Main(string[] args)    {        int[] source = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };        Indent("Source");        source.ShowItems();                int[] filterResult = Filter(x => x > 5, source);        Indent("Filter, item more than 5");        filterResult.ShowItems();        int[] mapResult = Map(x => x * 2, source);        Indent("Map, multiple with 2");        mapResult.ShowItems();        int reduceResult = Reduce((x, y) => x + y, source);        Indent("Reduce");        new[] { reduceResult }.ShowItems();        Console.ReadKey();    }}