A common technique in functional programming is the concept of currying. Currying is the process of transforming a function that accepts multiple parameters into a series of functions, each of which accept a single function. Take the following definition of foo:

    fun foo(a: String, b: Int) : Boolean 

The curried form would look like the following:

    fun foo(a: String): (Int) -> Boolean 

Note that the curried foo returns a second function, which in turn, when invoked with an Int, would return the Boolean as before. Currying is a useful technique for allowing functions with multiple parameters to work with other functions that only accept single arguments.

Currying is related to the idea of partial application. Partial application is the process by which some, but not all, of the parameters of a function are specified in advance, returning a new function that accepts the missing parameters. The parameters that have been given are said to be fixed...