つらぽよい Conditional

つらぽよ.idr

module Main

class Conditional a where
  toBool : a -> Bool

instance Conditional Bool where
  toBool = id

instance Conditional String where
  toBool "" = False
  toBool _  = True

(&&&&&) : (Monad m, Conditional a) => m a -> m a -> m a
m &&&&& k = do { x <- m ; if toBool x then k else return x }

main : IO ()
main = do
  x <- (&&&&&) getLine getLine
  putStr $ "\"" ++ x ++ "\""