[swift-evolution] Extending the for loop to have multiple clauses

[ilya]

You can define a 'times' operation to work with any sequences, e.g.

import Foundation

enum Suits: String {
    case Spades = "♠"
    case Hearts = "♥"
    case Diamonds = "♦"
    case Clubs = "♣"
}

let suits:[Suits] = [.Spades, .Hearts, .Diamonds, .Clubs]
let ranks = ["A", "K", "Q", "J", "10", "9", "8", "7", "6", "5", "4", "3",
"2"]

infix operator ⨉ {}

func ⨉<A:SequenceType, B:SequenceType>(lhs: A, rhs: B)
    -> [(A.Generator.Element, B.Generator.Element)] {

    return lhs
        .map{ left in rhs.map{ right in (left, right) }}
        .reduce([], combine: +)
}

[1, 2] ⨉ [3, 4]

func shuffled() -> [String] {
    var cards:[String] = []

    for (suit, rank) in suits ⨉ ranks {
        let random = Int(abs(rand())) % (cards.count + 1)
        cards.insert(suit.rawValue + rank, atIndex: random)
    }

    return cards
}

shuffled().joinWithSeparator(" ")




On Wed, Dec 9, 2015 at 23:00 Chris Eidhof via swift-evolution <
swift-evolution at swift.org> wrote:

> I think it could be really nice to extend the for-loop so that it can have
> multiple clauses. Much like in the if-let with multiple clauses, I could
> imagine a for-loop with multiple clauses:
>
> var cards: [(Suit,Rank)] = []
> for x in suits, y in ranks {
>   cards.append((x,y))
> }
>
> This would be the same as writing:
>
> var cards: [(Suit,Rank)] = []
> for x in suits {
>   for y in ranks {
>     cards.append((x,y))}
>   }
> }
>
> You could also do something like:
>
> for x in input1, y in (x..<end) {
>    // Do something with (x,y)
> }
>
> In fact, once we would have that, we could combine both if-let and for,
> and make it more general, to end up with something like Haskell’s
> do-notation or C#’s LINQ. But that might be taking it too far...
>
> Chris
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
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