Control.Monad.Validate.Class

Documentation

class (Monad m, Semigroup e) => MonadValidate e m | m -> e where

The class of validation monads, intended to be used to validate data structures while collecting errors along the way. In a sense, MonadValidate is like a combination of MonadError and MonadWriter, but it isn’t entirely like either. The two essential differences are:

1. Unlike throwError, raising an error using refute does not always abort the entire computation—it may only abort a local part of it.
2. Unlike tell, raising an error using dispute still causes the computation to globally fail, it just doesn’t affect local execution.

For a more thorough explanation, with examples, see the documentation for ValidateT.

Minimal complete definition

Nothing

Methods

refute :: e -> m a

Raises a fatal validation error. Aborts the current branch of the validation (i.e. does not return).

>>> runValidate (refute ["boom"] >> refute ["bang"])
Left ["boom"]

dispute :: e -> m ()

Raises a non-fatal validation error. The overall validation fails, and the error is recorded, but validation continues in an attempt to try and discover more errors.

>>> runValidate (dispute ["boom"] >> dispute ["bang"])
Left ["boom", "bang"]

tolerate :: m a -> m (Maybe a)

tolerate m behaves like m, except that any fatal errors raised by refute are altered to non-fatal errors that return Nothing. This allows m’s result to be used for further validation if it succeeds without preventing further validation from occurring upon failure.

>>> runValidate (tolerate (refute ["boom"]) >> refute ["bang"])
Left ["boom", "bang"]

Since: 1.1.0.0

refute :: (MonadTrans t, MonadValidate e m', m ~ t m') => e -> m a

Raises a fatal validation error. Aborts the current branch of the validation (i.e. does not return).

>>> runValidate (refute ["boom"] >> refute ["bang"])
Left ["boom"]

dispute :: (MonadTrans t, MonadValidate e m', m ~ t m') => e -> m ()

Raises a non-fatal validation error. The overall validation fails, and the error is recorded, but validation continues in an attempt to try and discover more errors.

>>> runValidate (dispute ["boom"] >> dispute ["bang"])
Left ["boom", "bang"]

tolerate :: (MonadTransControl t, MonadValidate e m', m ~ t m') => m a -> m (Maybe a)

tolerate m behaves like m, except that any fatal errors raised by refute are altered to non-fatal errors that return Nothing. This allows m’s result to be used for further validation if it succeeds without preventing further validation from occurring upon failure.

>>> runValidate (tolerate (refute ["boom"]) >> refute ["bang"])
Left ["boom", "bang"]

Since: 1.1.0.0

Instances

MonadValidate e m => MonadValidate e (MaybeT m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> MaybeT m a

dispute :: e -> MaybeT m ()

tolerate :: MaybeT m a -> MaybeT m (Maybe a)

(MonadValidate e m, Monoid w) => MonadValidate e (WriterT w m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> WriterT w m a

dispute :: e -> WriterT w m ()

tolerate :: WriterT w m a -> WriterT w m (Maybe a)

(MonadValidate e m, Monoid w) => MonadValidate e (WriterT w m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> WriterT w m a

dispute :: e -> WriterT w m ()

tolerate :: WriterT w m a -> WriterT w m (Maybe a)

(MonadValidate e m, Monoid w) => MonadValidate e (WriterT w m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> WriterT w m a

dispute :: e -> WriterT w m ()

tolerate :: WriterT w m a -> WriterT w m (Maybe a)

MonadValidate e m => MonadValidate e (StateT s m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> StateT s m a

dispute :: e -> StateT s m ()

tolerate :: StateT s m a -> StateT s m (Maybe a)

MonadValidate e m => MonadValidate e (StateT s m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> StateT s m a

dispute :: e -> StateT s m ()

tolerate :: StateT s m a -> StateT s m (Maybe a)

MonadValidate e m => MonadValidate e (ReaderT r m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> ReaderT r m a

dispute :: e -> ReaderT r m ()

tolerate :: ReaderT r m a -> ReaderT r m (Maybe a)

MonadValidate e m => MonadValidate e (IdentityT m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> IdentityT m a

dispute :: e -> IdentityT m ()

tolerate :: IdentityT m a -> IdentityT m (Maybe a)

MonadValidate e m => MonadValidate e (ExceptT a m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> ExceptT a m a0

dispute :: e -> ExceptT a m ()

tolerate :: ExceptT a m a0 -> ExceptT a m (Maybe a0)

(Monad m, Semigroup e) => MonadValidate e (ValidateT e m)

Defined in Control.Monad.Validate.Internal

Methods

refute :: e -> ValidateT e m a

dispute :: e -> ValidateT e m ()

tolerate :: ValidateT e m a -> ValidateT e m (Maybe a)

(MonadValidate e m, Monoid w) => MonadValidate e (RWST r w s m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> RWST r w s m a

dispute :: e -> RWST r w s m ()

tolerate :: RWST r w s m a -> RWST r w s m (Maybe a)

(MonadValidate e m, Monoid w) => MonadValidate e (RWST r w s m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> RWST r w s m a

dispute :: e -> RWST r w s m ()

tolerate :: RWST r w s m a -> RWST r w s m (Maybe a)

(MonadValidate e m, Monoid w) => MonadValidate e (RWST r w s m)

Defined in Control.Monad.Validate.Class

Methods

refute :: e -> RWST r w s m a

dispute :: e -> RWST r w s m ()

tolerate :: RWST r w s m a -> RWST r w s m (Maybe a)