`std/core/functions`

std/core/src/functions.trb

Names for the three closure shapes that signatures take most: a question about one value, an effect on one value and a conversion of one value into another.

Each is an alias, so it is transparent: any closure or function of the shape fits, and the alias adds no type of its own. A closure without parameters has no name here, because () => Value is already as short as one.

alias Predicate

type Predicate<Value> = (value: Value) => Bool

A closure that answers a yes-or-no question about one value: what filter, find, any and takeWhile take.

Examples

fn countWhere(numbers: List<Int>, predicate: Predicate<Int>): Int {
  numbers.filter(predicate).count()
}

alias Action

type Action<Value> = (value: Value) => Void

A closure called for its effect on one value, with nothing to return: what forEach takes.

Examples

fn visit(names: List<String>, action: Action<String>) {
  names.forEach action
}

alias Transform

type Transform<Input, Output> = (value: Input) => Output

A closure that turns one value into another: what map takes, and the key of sorted and groupBy.

Examples

fn labels(numbers: List<Int>, transform: Transform<Int, String>): List<String> {
  numbers.map(transform).toList()
}