#lang rhombus/static

// we can use `matches` to check the shape of datum
[1, 2] matches [_, _] // #true
[1, 2] matches [_, _, _] // #false

// itself can be a placeholder to indicate an abstraction!
def sum = (_ + _)
sum(1, 2) // 3

[1, 2, 3].map((_ * 2))