Combining Higher Order Functions in C#
Join the DZone community and get the full member experience.
Join For FreeSay I have a higherorderfunction, ‘applier’, that takes another function and some arguments, applies the function to the arguments and returns the results multiplied by two:
Func<Func<int, int, int>, int, int, int> applier = (f, x, y) => f(x, y) * 2;
Now let’s say we have a function, ‘multiplier’ that simply multiplies two numbers:
Func<int, int, int> multiplier = (a, b) => a*b;
How can we combine applier and multiplier so that we end up with a function that simply multiplies two numbers and doubles the result?
First we curry applier:
var curried = Functional.Curry(applier);
So now ‘curried’ looks something like this:
Func<Func<int, int, int>, Func<int, Func<int, int>>> curried = f => x => y => f(x, y)*2;
It’s a function that takes a function and returns a function. So if we call it passing in ‘multiplier’ we should get back a function that does what we want:
var curriedCombined = curried(multiplier);
The only problem with ‘curriedCombined’ is that it’s in this curried form:
Func<int, Func<int, int>> curriedCombined = x => y => (x*y)*2;
So let’s DeCurry it (is there a better term for this?):
var combined = Functional.DeCurry(curriedCombined);
Now we have our target function. We can call it just like a normal delegate with two arguments:
Console.WriteLine("combined(4) = {0}", combined(4, 4));
Which outputs 32 as expected.
So now we have a nice mechanical way of turning higherorderfunctions into normal functions by doing the following:
 Curry the higherorderfunction
 Pass the function(s) that supply the function argument(s) into the curried version.
 DeCurry
All I have to do now is some serious reflection and I’ll have a working CurryFacility.
Here is my Functional class (stolen from Oliver Sturm)
using System;
namespace Mike.AdvancedWindsorTricks.Model
{
public class Functional
{
public static Func<T1, Func<T2, T3>> Curry<T1, T2, T3>(Func<T1, T2, T3> function)
{
return a => b => function(a, b);
}
public static Func<T1, Func<T2, Func<T3, T4>>> Curry<T1, T2, T3, T4>(Func<T1, T2, T3, T4> function)
{
return a => b => c => function(a, b, c);
}
public static Func<T1, Func<T2, Func<T3, Func<T4, T5>>>> Curry<T1, T2, T3, T4, T5>(Func<T1, T2, T3, T4, T5> function)
{
return a => b => c => d => function(a, b, c, d);
}
public static Func<T1, T2, T3> DeCurry<T1, T2, T3>(Func<T1, Func<T2, T3>> function)
{
return (a, b) => function(a)(b);
}
public static Func<T1, T2, T3, T4> DeCurry<T1, T2, T3, T4>(Func<T1, Func<T2, Func<T3, T4>>> function)
{
return (a, b, c) => function(a)(b)(c);
}
public static Func<T1, T2, T3, T4, T5> DeCurry<T1, T2, T3, T4, T5>(Func<T1, Func<T2, Func<T3, Func<T4, T5>>>> function)
{
return (a, b, c, d) => function(a)(b)(c)(d);
}
}
}
Published at DZone with permission of Mike Hadlow, DZone MVB. See the original article here.
Opinions expressed by DZone contributors are their own.
Trending

FrontEnd: Cache Strategies You Should Know

AI Technology Is Drastically Disrupting the Background Screening Industry

Designing a New Framework for Ephemeral Resources

5 Key Concepts for MQTT Broker in Sparkplug Specification
Comments