In continuation of https://gist.github.com/yas375/69d8643ff7d98b137cc2f8201c3e58fc

my.swift

func double(value: Int) -> Int {
  print("double \(value)")
  return value * 2
}

func triple(value: Int) -> Int {
  print("triple \(value)")
  return value * 3
}

func filter(value: Int) -> Bool {
  print("filter \(value)")
  return value < 10
}

let bs = [1, 4].lazy
  .map(double)
  .map(triple)
  .filter(filter)

print(Array(bs.generate()))

output

double 1
triple 2
filter 6
double 4
triple 8
filter 24
[6]