Control.Monad.Trans.Maybe

The parameterizable maybe monad, obtained by composing an arbitrary monad with the Maybe monad.

Computations are actions that may produce a value or exit.

The return function yields a computation that produces that value, while >>= sequences two subcomputations, exiting if either computation does.

Transform the computation inside a MaybeT.

• runMaybeT (mapMaybeT f m) = f (runMaybeT m)

Convert a Maybe computation to MaybeT.

Convert a MaybeT computation to ExceptT, with a default exception value.

Convert a ExceptT computation to MaybeT, discarding the value of any exception.

Lift a callCC operation to the new monad.

Lift a catchE operation to the new monad.

Lift a listen operation to the new monad.

Lift a pass operation to the new monad.