[Haskell-beginners] Getting a specified number of lines from stdin

[Anton Felix Lorenzen]

You can define a mixture of takeWhile and sequence as:

takeWhileM :: (a -> Bool) -> [IO a] -> IO [a]
takeWhileM _ [] = return []
takeWhileM p (x:xs) = do
     e <- x
     if p e
         then do xs' <- takeWhileM p xs
                 return (e : xs')
         else return []

and then write:

ghci> takeWhileM (/="") (repeat getLine) >>= print
asdf
asdf

["asdf","asdf"]

Yours,
Anton Felix Lorenzen