functional-workshop

functional programming principles applied in C#

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Curried Functions

Named after mathematician Haskell Curry, currying is the process of transforming an n-ary function f that takes arguments t1, t2, …, tn into a unary function that takes t1 and yields a new function that takes t2, and so on, ultimately returning the same result as f once the arguments have all been given. In other words, an n-ary function with signature

(T1, T2, ..., Tn) → R

when curried has signature

(T1) (T2) ... (Tn) → R

By itself this technique is pretty useless, but it does enable the use of partial application.

using System;
using static System.Console;

internal class TestCurriedFunctions
{
    internal static void Run()
    {
        WriteLine(Greeter("Hello")("World"));
        WriteLine(Sum(5)(18));
    }

    private static Func<string, Func<string, string>> Greeter =>
        (firstName) => (lastName) => $"{firstName} {lastName}";

    private static Func<int, Func<int, int>> Sum =>
        (lhs) => (rhs) => lhs + rhs;
}