Turning a function that takes multiple arguments into a series of functions that each take one argument is called currying. For example, take this function with three arguments:

								func login(email: String, pw: String, success: (Bool )-> ())

							

We can turn it into a series of functions where the arguments can be applied one after another using Swift's special syntax for curried functions:

								func curriedLogin1(email: String);(pw: String)(success: Bool -> ())

							

More interestingly, we can also write a generic function that does the currying for us. The following one works on functions with three arguments, but we could write variants for any number of arguments:

								func curry<A, B, C, R>(f: (A, B, C) -> R) -> (A )-> (B )-> (C )-> R {
    return { a in { b in { c in f(a, b, c) } } }
}

let curriedLogin2 = curry(login)

							

Now we can apply the arguments one by one:

								let f = curriedLogin2("foo")("bar")
f { println("success: \($0)") }

							

You're actually using this pattern all the time without even noticing: instance methods in Swift are curried functions that take the instance as first argument.

Stay tuned for next week's snippet for a cool application of this.