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Curryfy

Provides strongly typed extensions methods for C# delegates to take advantages of functional programming techniques, like currying and partial application.
Concepts very well known in functional languages like Haskell, F#, Scala, etc.

What and Why?

Curryfy offers strongly typed extensions that lets you take some benefits of functional programming:

• easy reuse of more abstract functions.
• create new functions out of an existing function by fixing some parameters
• convenient way to partially apply a function

Features

• Extension methods for Currying and UnCurrying
• Extension methods for Partial Application, with 3 possible approaches
• Robust and strongly typed
• Self contained with no dependencies
• Easily installed through NuGet
• Supports .NET 3.5+ and .NET Core (.NET Standard 2.0+)

Installation

Simply reference Curryfy.dll and you are good to go!

Curryfy is also available via NuGet:

PM> Install-Package Curryfy  

Or visit: https://www.nuget.org/packages/Curryfy

Using the library

All helper methods are available as extension methods under the Curryfy namespace.
They are divided into 7 static classes to avoid method signature ambiguities:

• CurryExtensions class
  Provides methods for curry and uncurry on Func delegates.

• PartialIncrementalActionExtensions and PartialIncrementalFuncExtensions classes
  Provides methods for partial application on Func and Action delegates, respecting parameters order.
  You can pass only the first argument, only the first and second, only the first, second and third, and so on.
  So for a delegate with N parameters, there are N-1 overloads available.
  The -1 overload not avaible is the one with all parameters, which is the delegate itself.

• PartialSubsetActionExtensions and PartialSubsetFuncExtensions classes
  Provides methods for partial application on delegates, without respecting parameters order.
  You can pass arguments arbitrarily, regardless of its positions.
  So for a delegate with N parameters, there are (2^N)-2 (2 to the power of N, minus 2) overloads available (see powerset).
  The -2 overloads not avaible are the one with no parameters and the one with all parameters, which is the delegate itself.

• PartialDiscardActionExtensions and PartialDiscardFuncExtensions classes
  Provides methods for partial application on delegates, without respecting parameters order.
  It is similar to PartialSubset classes, however in the method call these one rely on arguments
  position rather than their names. Which can be more convenient in some situations.

Core concepts

Consider the code snippet below as part of all examples:

Func<int, int, int, int> add = (a, b, c) => a + b + c;

Partial Application

Partial application is the process of pass part of the arguments of a function, returning a function that receives the rest of the arguments. If you provide 1 out of 3 arguments, it'll return a function that takes 2 arguments. If you provide 2 out of 3 arguments, it'll return a function that takes 1 argument.

This feature is available for delegates Func and Action through ApplyPartial extension method.

This method has 1232 overloads.

using static Curryfy.PartialIncrementalFuncExtensions;

var add12 = add.ApplyPartial(5, 7); // add12 is Func<int, int>
var add5 = add.ApplyPartial(5);     // add5 is Func<int, int, int>
var x = add12(3) + add5(7, 3);      // 15 + 15

Note that using the incremental approach, we can only pass the third argument after pass the first and second.
This approach is used by languages like Haskell and F#.
However using the subset approach, we can pass arguments arbitrarily.
You can pass the only first and the third arguments of a function with 5 parameters, for example.

using static Curryfy.PartialSubsetFuncExtensions;

var add3 = add.ApplyPartial(arg3: 3);   // parameter c receives 3
var add10 = add3.ApplyPartial(arg2: 7); // parameter b receives 7
var x = add10(5);                       // parameter a receives 5
Console.WriteLine(x);                   // x = 15

Using the discard approach, we can rely on arguments position instead of name.
This approach is used by languages like Scala.
The previous example using discard approach:

using static Curryfy.PartialDiscardFuncExtensions;
using static Curryfy.Discard;

var add3 = add.ApplyPartial(_, _, 3);   // parameter c receives 3
var add10 = add3.ApplyPartial(_, 7);    // parameter b receives 7
var x = add10(5);                       // parameter a receives 5
Console.WriteLine(x);                   // x = 15

Note: when using C# discard feature in the same scope that discard approach, you should use double underscore (__) instead of single underscore (_) in the method call. That is, instead of sum(_, 3) is sum(__, 3).
If not using in same scope single underscore is fine.

Which one of these 3 approaches fits better depending of situation. For example, if you have a function with 4 parameters and want to pass only the third, might be more interesting to specify the desired argument f(arg3: "foo") rather than use discard f(_, _, "foo", _). In general:

• If you want to pass arguments respecting order, incremental approach is better.
• If you want to pass arguments arbitrarily and skip most arguments, subset approach tends to fit better.
• If you want to pass arguments arbitrarily and pass most arguments, discard approach tends to fit better.

If you want, it is possible to enable more than one approach at the same time, for example:

using static Curryfy.PartialIncrementalFuncExtensions;
using static Curryfy.PartialDiscardFuncExtensions;
using static Curryfy.Discard;

Func<string, char, int, bool> f = (s, c, i) => s[i] == c;

var g = f.ApplyPartial(_, 'b', 1); // using discard approach, g is Func<string, bool>

var h = f.ApplyPartial("ab", 'b'); // using incremental approach, h is Func<int, bool>

Currying

Currying is the process of splitting a function with multiple arguments into a nested chain of one argument functions. Therefore a curried function is a function which takes its arguments one at a time, returning a new function at each step.

This feature is available for Func delegates through Curry extension method.

This method has 15 overloads.

using static Curryfy.CurryExtensions;

var addCurried = add.Curry();   // addCurried is Func<int, Func<int, Func<int, int>>>

var add5 = addCurried(5);       // add5 is Func<int, Func<int, int>>
var add12 = add5(7);            // add12 is Func<int, int>
var x = add12(3);               // x is 15

var y = addCurried(5)(7)(3);    // y is 15

UnCurrying

UnCurrying is the process of transforms a curried function in a function which takes all of its arguments at once.

This feature is available for Func delegates through UnCurry extension method.

This method has 15 overloads.

using static Curryfy.CurryExtensions;

var curried = add.Curry();            // curried is Func<int, Func<int, Func<int, int>>>
var add5 = curried(5);                // add5 is Func<int, Func<int, int>>
var uncurried = add5.UnCurry();       // uncurried is Func<int, int, int>

var x = uncurried(7, 3) + curried(5)(7)(3);    // 15 + 15