Rash thoughts about .NET, C#, F# and Dynamics NAV.

In the last couple of days I started to write some posts about Currying and Partial application:

• Partial application in F# and C#
• Why do we need partial application? – Part 1 of n – Fluent interfaces and piping

This time I want to show you how we can write a higher-order function which allows us to curry another function. Remember the multiplication function from the first post and it’s curried form:

Currying

The question is: how can we automate this transformation process? Remember we want to have the curryied form for partial application:

Let’s look at the signature of the desired Curry-function: in our case it has to take Func<int, int, int> and returns Func<int, Func<int, int>>.

If we generalize the ints to generic parameters and fix the signature then the implementation is trivial (Compiler Driven Programming). There is exactly one way to make this work:

The F# implementation does exactly the same, but without all the annoying the type hints:

Uncurrying

Of course you can undo the currying by applying a generic Uncurry-function:

And in F# this looks like this:

Libraries

Currying and Uncurrying are two very important concepts in functional programming so they are included in a couple of libraries:

• You can find it at the top of the Prelude in FSharpx (read more).
• You can find it in the Haskell Prelude.
• You can find similar functions in Scalaz.
• Adrian Lang wrote a library called partial-js which allows to do something similar in JavaScript.