lazy I/Oで出力の順番が意図したとおりにならない例

UnsafeIO.hs

module Main where
import System.IO.Unsafe (unsafeInterleaveIO)

test f = do
  line1 <- f
  line2 <- f
  putStrLn $ "line2: " ++ line2
  putStrLn $ "line1: " ++ line1

main :: IO ()
main = do
  putStrLn "lazy"
  test $ unsafeInterleaveIO getLine
  putStrLn "strict"
  test getLine

% ./UnsafeIO
lazy
aaa
line2: aaa
bbb
line1: bbb
strict
aaa
bbb
line2: bbb
line1: aaa