msum package:invertible

msumFirst :: (MonoidalAlt f, Traversable t) => t (f a) -> f a
invertible Control.Invertible.Monoidal
Fold a structure with >| (|<), thus always applying the input to the first (last) item for generation.
msumIndex :: MonoidalAlt f => [f ()] -> f Int
invertible Control.Invertible.Monoidal
Try a list of monoidal actions in sequence, producing the index of the first successful action, and evaluating the action with the given index.
msumLast :: (MonoidalAlt f, Traversable t) => t (f a) -> f a
invertible Control.Invertible.Monoidal
Fold a structure with >| (|<), thus always applying the input to the first (last) item for generation.