Control.Monad.Abort

Monads that can immediately return a result

class Monad m => MonadAbort m where

Associated Types

type AbortResultType m

Methods

abort :: AbortResultType m -> m a

Instances

MonadAbort m => MonadAbort (ListT m)

MonadAbort m => MonadAbort (MaybeT m)

MonadAbort m => MonadAbort (IdentityT m)

Monad m => MonadAbort (AbortT r m)

(MonadAbort m, Error e) => MonadAbort (ErrorT e m)

MonadAbort m => MonadAbort (ReaderT r m)

MonadAbort m => MonadAbort (StateT s m)

MonadAbort m => MonadAbort (StateT s m)

(MonadAbort m, Monoid w) => MonadAbort (WriterT w m)

(MonadAbort m, Monoid w) => MonadAbort (WriterT w m)

(MonadAbort m, Monoid w) => MonadAbort (RWST r w s m)

(MonadAbort m, Monoid w) => MonadAbort (RWST r w s m)

The Abort monad

type Abort r = AbortT r Identity

An abort monad, parametrized by the type r of the value to return.

runAbort

Arguments

:: Abort r r

the monadic computation to run

-> r

the result of the computation

Execute the abort monad computation and return the resulting value.

The AbortT monad transformer

newtype AbortT r m a :: * -> (* -> *) -> * -> *

An abort monad transformer parametrized by

• r - the value that will ultimately be returned; and
• m - the inner monad.

The AbortT type wraps a monadic value that is either

• Left r, which indicates that the monadic computation has terminated with result r and so all further steps in the computation should be ignored; or
• Right a, which indicates that the computation is proceding normally and that its current value is a.

Constructors

AbortT

Fields

unwrapAbortT :: m (Either r a)

Instances

MonadTrans (AbortT r)

Monad m => Monad (AbortT r m)

Functor m => Functor (AbortT r m)

Applicative m => Applicative (AbortT r m)

MonadIO m => MonadIO (AbortT r m)

MonadRWS m => MonadRWS (AbortT r m)

MonadWriter m => MonadWriter (AbortT r m)

MonadState m => MonadState (AbortT r m)

MonadReader m => MonadReader (AbortT r m)

MonadError m => MonadError (AbortT r m)

MonadCont m => MonadCont (AbortT r m)

Monad m => MonadAbort (AbortT r m)

type WriterType (AbortT r m) = WriterType m

type StateType (AbortT r m) = StateType m

type EnvType (AbortT r m) = EnvType m

type ErrorType (AbortT r m) = ErrorType m

type AbortResultType (AbortT r m) = r

runAbortT

Arguments

:: forall (m :: * -> *). Monad m

=> AbortT r m r

the monadic computation to run

-> m r

the (monadic) result of the computation

Execute the abort monad computation and return the resulting (monadic) value.

AbortT operations

mapAbortT :: (m (Either r a) -> n (Either r' b)) -> AbortT r m a -> AbortT r' n b