Swift Attempt Function

Swift Attempt Function.swift

/*
 * attempt takes a function that does not accept optional values
 * and returns a new function that will work as usual with non-optional values
 * and return nil when passed an optional value
 */
 
func attempt<T,U>(f: T -> U)-> T? -> U? {
    return { y in
        if let x = y {
            return f(x)
        }
        else {
            return nil
        }
    }
}

// Example

var arr = [3.2, 2.1, 1.0]
let x: Double? = 5.0 // Optional value

// tl;dr
attempt(arr.append)(x)
let y = attempt(sqrt)(x)

//
// Motivation
//

// No return value

arr.append(x)                         // Error
if let x = x { arr.append(x) }        // Annoying
if (x != nil) { arr.append(x!) }      // Gross
attempt(arr.append)(x)                // >> Yay! <<

// Return value

let y = sqrt(x)                       // Error
if let x = x { let y = sqrt(x) }      // Annoying
let y = (x != nil) ? sqrt(x!) : nil   // Gross
let y = attempt(sqrt)(x)              // >> Yay! <<

// Note that the "annoying" example for 'return value' is especially
// horrible because all code that uses y must be within the brackets