F# curried function

Question

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

Answer 1

You know you can map a function over a list? For example, mapping a function to add one to each element of a list:

> List.map ((+) 1) [1; 2; 3];;
val it : int list = [2; 3; 4]

This is actually already using currying because the (+) operator was used to create a function to add one to its argument but you can squeeze a little more out of this example by altering it to map the same function of a list of lists:

> List.map (List.map ((+) 1)) [[1; 2]; [3]];;
val it : int list = [[2; 3]; [4]]

Without currying you could not partially apply these functions and would have to write something like this instead:

> List.map((fun xs -> List.map((fun n -> n + 1), xs)), [[1; 2]; [3]]);;
val it : int list = [[2; 3]; [4]]