A way to describe a function using a wrapper struct

Abstract - Function.md

Function

let addition = Function(call: { (c: Int, d: Int) -> Int in return c + d }, description: "$0 + $1")

print( addition )
// Prints "$0 + $1"

print( addition.call((5,3)) )
// Prints "8"

The Function wrapper-struct is a struct designed to make a specific function custom-string-convertible, a.k.a. printable.

Function.swift

struct ThrowingFunction<Operand, Result> : CustomStringConvertible {
  var call : (Operand) throws -> Result
  var description : String
}

struct Function<Operand, Result> : CustomStringConvertible {
  var call : (Operand) -> Result
  var description : String
}