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
}

let xs = [1, 4]

let bs = Array(xs.lazy
  .map(double)
  .map(triple)
)

print("result: \(bs)")

output

double 1
triple 2
double 4
triple 8
result: [6, 24]

I've got the expected behavior with filter in https://gist.github.com/yas375/e63416596701e6cece2e2158cc0b8c1d