whileを使ったループ(多分分かりやすくはない)

while.hs

import Control.Monad

while :: (Monad m) => (a -> Bool) -> m a -> m a
while f m = do
  a <- m
  when (f a) $ while f m >> return ()
  return $ a

main = do
  putStrLn $ "Can you guess the number I have?"
  while (\a -> a /= 42) $ do
    a <- getLine
    putStrLn $ "You said:" ++ a
    return $ read a
  putStrLn "That's right!"

while_output.txt

Can you guess the number I have?
> 10
You said:10
> 20
You said:20
> 43
You said:43
> 42
You said:42
That's right!