gistfile1.txt

//
//NonEmpty
//DataSiteOne
//
//Created by Huang, Eric on 4/12/18
//Copyright © 2018 Merrill Corporation. All rights reserved.

import Foundation

public protocol NonEmpty {
    associatedtype Collection: Swift.Collection
    var head: Collection.Iterator.Element { get }
    var tail: Collection { get }
}

extension NonEmpty {
    
    var count: Int {
        return tail.count.advanced(by: 1)
    }
    
    public var first: Collection.Iterator.Element {
        return self.head
    }
}

extension NonEmpty where Collection: RandomAccessCollection {
    
    public var last: Collection.Iterator.Element {
        return self.tail.last ?? self.head
    }
}

struct NonEmptySet<Element>: NonEmpty where Element: Hashable {
    let head: Element
    let tail: Set<Element>
}

extension NonEmptySet {
    
    init(_ head: Element, _ tail: Element...) {
        self.init(head: head, tail: Set(tail).subtracting([head]))
    }
    
    init(_ head: Element) {
        self.init(head: head, tail: Set())
    }
}

func == <T>(lhs: NonEmptySet<T>, rhs: NonEmptySet<T>) -> Bool {
    return lhs.head == rhs.head && lhs.tail == rhs.tail
}

func != <T>(lhs: NonEmptySet<T>, rhs: NonEmptySet<T>) -> Bool {
    return lhs.head != rhs.head || lhs.tail != rhs.tail
}

infix operator +|: AdditionPrecedence

precedencegroup AdditionPrecedence {
    associativity: left
}

func +| <T>(head: T, tail: Set<T>) -> NonEmptySet<T> {
    return NonEmptySet<T>(head: head, tail: tail.subtracting([head]))
}

extension Array where Element: Hashable {
    
    init(_ nonEmpty: NonEmptySet<Element>) {
        self = [nonEmpty.head] + Array(nonEmpty.tail)
    }
}