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Asked: 2026-05-11T04:12:29+00:00

I read This article and i found it interesting. To sum it up for

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I read This article and i found it interesting.

To sum it up for those who don’t want to read the entire post. The author implements a higher order function named Curry like this (refactored by me without his internal class):

 public static Func<T1, Func<T2, TResult>>               Curry<T1, T2, TResult>(this Func<T1, T2, TResult> fn)  {      Func<Func<T1, T2, TResult>, Func<T1, Func<T2, TResult>>> curry =       f => x => y => f(x, y);      return curry(fn);  }

That gives us the ability to take an expression like F(x, y) eg. 

Func<int, int, int> add = (x, y) => x + y;

and call it in the F.Curry()(x)(y) manner;

This part i understood and i find it cool in a geeky way. What i fail to wrap my head around is the practical usecases for this approach. When and where this technique is necessary and what can be gained from it?

Thanks in advance.

Edited: After the initial 3 responses i understand that the gain would be that in some cases when we create a new function from the curried some parameters are not re evalued. I made this little test in C# (keep in mind that i’m only interested in the C# implementation and not the curry theory in general):

public static void Main(string[] args) {     Func<Int, Int, string> concat = (a, b) => a.ToString() + b.ToString();     Func<Int, Func<Int, string>> concatCurry = concat.Curry();     Func<Int, string> curryConcatWith100 = (a) => concatCurry(100)(a);      Console.WriteLine(curryConcatWith100(509));     Console.WriteLine(curryConcatWith100(609)); }      public struct Int     {         public int Value {get; set;}          public override string ToString()         {              return Value.ToString();         }          public static implicit operator Int(int value)         {             return new Int { Value = value };         }     }

On the 2 consecutive calls to curryConcatWith100 the ToString() evaluation for the value 100 is called twice (once for each call) so i dont see any gain in evaluation here. Am i missing something ?

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1 Answer

  1. Its easier to first consider fn(x,y,z). This could by curried using fn(x,y) giving you a function that only takes one parameter, the z. Whatever needs to be done with x and y alone can be done and stored by a closure that the returned function holds on to.

    Now you call the returned function several times with various values for z without having to recompute the part the required x and y.

    Edit:

    There are effectively two reasons to curry.

    Parameter reduction

    As Cameron says to convert a function that takes say 2 parameters into a function that only takes 1. The result of calling this curried function with a parameter is the same as calling the original with the 2 parameters.

    With Lambdas present in C# this has limited value since these can provide this effect anyway. Although it you are use C# 2 then the Curry function in your question has much greater value.

    Staging computation

    The other reason to curry is as I stated earlier. To allow complex/expensive operations to be staged and re-used several times when the final parameter(s) are supplied to the curried function.

    This type of currying isn’t truely possible in C#, it really takes a functional language that can natively curry any of its functions to acheive.

    Conclusion

    Parameter reduction via the Curry you mention is useful in C# 2 but is considerably de-valued in C# 3 due to Lambdas.

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