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Lambda Wrapping to Guard Evaluation in Swift
// Imagine we have a function that curries
// That is, multiply takes in an integer a
// and returns a fuction that takes in another
// integer b that will return a * b
func multiply(a: Int) -> Int -> Int {
println("I got the first thing")
return { b in
println("I got the second thing")
return a * b
}
}
// Note we can use such a function to muliply 3 and 5 as follows
multiply(3)(5)
// First we will examine the case of no guard
let multiplyBy3 = multiply(3) // -> "I got the first thing"
println("I'm waiting...") // -> "I'm waiting"
let result = multiplyBy3(5) // -> "I got the second thing"
println("The result is \(result)") // -> "The result is 15"
// Notice that we printed "I'm waiting" in between
// receiving the first and second argument
// Now we will wrap our first line of code in a lambda (closure)
let multiplyBy3 = { x in multiply(3)(x) } // ->
println("I'm waiting...") // -> "I'm waiting"
let result = multiplyBy3(5) // -> "I got the first thing"; -> "I got the second thing"
println("The result is \(result)") // -> "The result is 15"
// Notice that we printed "I'm waiting before we even recieved
// the first argument! This is because we created a new function
// that WILL pass three into multiply whenever it recieves another
// arugment x to pass in as well. Neat!
// Note that I wanted to make a function guard that would work like
// above with the syntax guard(multiply(3)), but it turns out that
// you cannot use @autoclosures to caputre partially evaluated
// functions in Swift, darn.
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