addPrefix.swift

func addPrefix(c : Character) -> (String) -> String {
    return  {
        (currentString : String) -> String in
        let result = String(c) + currentString
        return result
    }
}

//OR

func insertPrefix(s : String, c : Character) -> String {
    return String(c) + s
}
func addPrefix(c : Character) -> (String) -> String {
    return  {
        (currentString : String) -> String in
        return insertPrefix(currentString, c)
    }
}

var ar = ["aaa", "bbb", "ccc", "ddd"]
ar.map(addPrefix("z")) //OUTPUT -> ["zaaa", "zbbb", "zccc", "zddd"]