Process collections with callbacks

Lists provide map, filter, fold, and foreach. These methods accept functions or lambdas. Use them for reward tables, prices, and scores.

Method	Callback parameters	Result
map	Current element	A new list of callback results
filter	Current element	Elements for which the callback returns true
fold(initial)	Accumulator, current element	The final accumulator
foreach	Current element	Executes the callback for each element

Calculate rewards

func main() {
    var scores = [1, 2, 3, 4]
    var bonus = 10
    var rewards = scores.map { it + bonus }
    var eligible = scores.filter { it >= 3 }
    var total = scores.fold(0) { sum, score -> sum + score }
    print(rewards)
    print(eligible)
    print(total)
}

rewards is [11, 12, 13, 14]. eligible is [3, 4]. total is 10. Use it for a callback with one parameter, or specify a parameter name.

Reuse a function

func doubled(value: int): int {
    return value * 2
}

func main() {
    var prices = [5, 10, 15]
    var saleValues = prices.map(doubled)
    print(saleValues)
}

The callback determines the result type of map. For example, scores.map { it > 2 } produces list<bool>.

Skip one callback invocation

func main() {
    var values = [1, 2, 3]
    values.foreach {
        if (it == 2) {
            return
        }
        print(it)
    }
    print("Finished")
}

This example prints 1, 3, and Finished. A return inside the callback ends that invocation. Processing then continues with the remaining elements.

fold processes elements in list order. For an empty list, it returns the initial value. A callback can read outer variables. It captures their values when the callback is created. Read Lambdas for function types and trailing lambda syntax.