F# curried function

Question

Anyone have a decent example, preferably practical/useful, they could post demonstrating the concept?

Answer 1

It's a fairly simple process. Take a function, bind one of its arguments and return a new function. For example:

let concatStrings left right = left + right
let makeCommandPrompt= appendString "c:\> "

Now by currying the simple concatStrings function, you can easily add a DOS style command prompt to the front of any string! Really useful!

Okay, not really. A more useful case I find is when I want to have a make a function that returns me data in a stream like manner.

let readDWORD array i = array[i] | array[i + 1] << 8 | array[i + 2] << 16 | 
    array[i + 3] << 24 //I've actually used this function in Python.

The convenient part about it is that rather than creating an entire class for this sort of thing, calling the constructor, calling obj.readDWORD(), you just have a function that can't be mutated out from under you.