Thomas Hartman
That's slick, but is there some way to use interact twice in the same program?
No :-)
t10 = let f = unlines . takeWhile (not . blank) . lines in do putStrLn "first time" interact f putStrLn "second time" interact f
this results in *** Exception: <stdin>: hGetContents: illegal operation (handle is closed) -}
Yes. Interacting uses hGetContents, and hGetContents semi-closes (or fully-closes) the handle. If you do it from GHCi, you only get to run your program once.
I also tried
t15 = let grabby = unlines . takeWhile (not . blank) . lines top = ("first time: " ++) . grabby . ("second time: " ++) . grabby in interact top
but that didn't work either: thartman@ubuntu:~/haskell-learning/lazy-n-strict>runghc sequencing.hs a first time: second time: a b b
Well - the input to the leftmost grabby is "second time" prepended to the input from the first, and then you prepend "first time" - so this makes sense. Something like this, perhaps: interact (\s -> let (first,second) = span (not . null) (lines s) in unlines ("first":first++"second":takeWhile (not.null) second))
If someone can explain the subtleties of using interact when you run out of stdio here, it would be nice to incorporate this into
hGetContents - there can only be one. -k -- If I haven't seen further, it is by standing in the footprints of giants