firstM :: Monad m => (a -> m c) -> (a, b) -> m (c, b)
firstM f (x, y) = liftM (\x' -> (x', y)) (f x)
firstM :: Monad m => (a -> m c) -> (a, b) -> m (c, b)
firstM f (x, y) = liftM (\x' -> (x', y)) (f x)
firstM f (x, y) = liftM (\x' -> (x', y)) (f x)