Array pattern matching

pattern-matching.swift

// the types of items that a template can be built up from, in the future I'd be interested in expanding this 
// to allow a wider range of options.
enum TemplateItem<T> {
    case Exact(T) // matches only this exact element
    case Either([T]) // matches any one of the elements given
    case LazySequence // matches any sequence of elements
}

// create a template to describe the pattern you want to look for in the array
let moreThanTemplate: [TemplateItem<String>] = [
  .Either(["more", "greater"]), 
  .LazySequence, 
  .Exact("than"), 
  .LazySequence
]

// I extended Array with a method with this signature:
// func matches(_: [TemplateItem<Element>]) -> [TemplateMatch<Element>]?
// given a template, it returns nil if there are no matches, otherwise an array of 'TemplateMatch'

// TemplateMatch is just a way to give some structure to results. 
// Either indicating a single element, or a sequence of elements
enum TemplateMatch<T> {
    case Single(T)
    case Sequence([T])
}

// create a text sentence to test the parser
let words = "more large blue shapes than small squares".componentsSeparatedByString(" ")

// if matches is non-nil then the `words` array matches the `moreThanTemplate` format
if let matches = words.matches(moreThanTemplate) {

    // check that the order if match items is as expected and at the same time assign components
    if case let (.Single, .Sequence(fragment1), .Single, .Sequence(fragment2)) = (matches[0], matches[1], matches[2], matches[3]) {
    
        print("more", fragment1, "than", fragment2)
        // more ["large", "blue", "shapes"] than ["small", "squares"]
    }
}