Safe Haskell	Trustworthy
Language	Haskell98

MonadLib

Contents

Types
Lifting
Effect Classes
Execution
- Eliminating Effects
- Nested Execution
Utility functions
Miscellaneous

Description

This library provides a collection of monad transformers that can be combined to produce various monads.

Synopsis

Types

The following types define the representations of the computation types supported by the library. Each type adds support for a different effect.

data Id a #

Computations with no effects.

Instances

Monad Id #
Methods (>>=) :: Id a -> (a -> Id b) -> Id b # (>>) :: Id a -> Id b -> Id b # return :: a -> Id a # fail :: String -> Id a #
Functor Id #
Methods fmap :: (a -> b) -> Id a -> Id b # (<$) :: a -> Id b -> Id a #
MonadFix Id #
Methods mfix :: (a -> Id a) -> Id a #
Applicative Id #
Methods pure :: a -> Id a # (<>) :: Id (a -> b) -> Id a -> Id b # (>) :: Id a -> Id b -> Id b # (<*) :: Id a -> Id b -> Id a #
BaseM Id Id #
Methods inBase :: Id a -> Id a #
RunM Id a a #
Methods runM :: Id a -> a #

data Lift a #

Computation with no effects (strict).

Instances

Monad Lift #
Methods (>>=) :: Lift a -> (a -> Lift b) -> Lift b # (>>) :: Lift a -> Lift b -> Lift b # return :: a -> Lift a # fail :: String -> Lift a #
Functor Lift #
Methods fmap :: (a -> b) -> Lift a -> Lift b # (<$) :: a -> Lift b -> Lift a #
MonadFix Lift #
Methods mfix :: (a -> Lift a) -> Lift a #
Applicative Lift #
Methods pure :: a -> Lift a # (<>) :: Lift (a -> b) -> Lift a -> Lift b # (>) :: Lift a -> Lift b -> Lift b # (<*) :: Lift a -> Lift b -> Lift a #
BaseM Lift Lift #
Methods inBase :: Lift a -> Lift a #
RunM Lift a a #
Methods runM :: Lift a -> a #

data IdT m a #

Adds no new features. Useful as a placeholder.

Instances

MonadT IdT #
Methods lift :: Monad m => m a -> IdT m a #
Monad m => Monad (IdT m) #
Methods (>>=) :: IdT m a -> (a -> IdT m b) -> IdT m b # (>>) :: IdT m a -> IdT m b -> IdT m b # return :: a -> IdT m a # fail :: String -> IdT m a #
Monad m => Functor (IdT m) #
Methods fmap :: (a -> b) -> IdT m a -> IdT m b # (<$) :: a -> IdT m b -> IdT m a #
MonadFix m => MonadFix (IdT m) #
Methods mfix :: (a -> IdT m a) -> IdT m a #
Monad m => Applicative (IdT m) #
Methods pure :: a -> IdT m a # (<>) :: IdT m (a -> b) -> IdT m a -> IdT m b # (>) :: IdT m a -> IdT m b -> IdT m b # (<*) :: IdT m a -> IdT m b -> IdT m a #
MonadPlus m => Alternative (IdT m) #
Methods empty :: IdT m a # (<\|>) :: IdT m a -> IdT m a -> IdT m a # some :: IdT m a -> IdT m [a] # many :: IdT m a -> IdT m [a] #
MonadPlus m => MonadPlus (IdT m) #
Methods mzero :: IdT m a # mplus :: IdT m a -> IdT m a -> IdT m a #
ContM m => ContM (IdT m) #
Methods callWithCC :: ((a -> Label (IdT m)) -> IdT m a) -> IdT m a #
AbortM m i => AbortM (IdT m) i #
Methods abort :: i -> IdT m a #
RunExceptionM m i => RunExceptionM (IdT m) i #
Methods try :: IdT m a -> IdT m (Either i a) #
RunWriterM m j => RunWriterM (IdT m) j #
Methods collect :: IdT m a -> IdT m (a, j) #
RunReaderM m j => RunReaderM (IdT m) j #
Methods local :: j -> IdT m a -> IdT m a #
ExceptionM m j => ExceptionM (IdT m) j #
Methods raise :: j -> IdT m a #
StateM m j => StateM (IdT m) j #
Methods get :: IdT m j # set :: j -> IdT m () #
WriterM m j => WriterM (IdT m) j #
Methods put :: j -> IdT m () #
ReaderM m j => ReaderM (IdT m) j #
Methods ask :: IdT m j #
BaseM m n => BaseM (IdT m) n #
Methods inBase :: n a -> IdT m a #
RunM m a r => RunM (IdT m) a r #
Methods runM :: IdT m a -> r #

data ReaderT i m a #

Add support for propagating a context of type i.

Instances

MonadT (ReaderT i) #
Methods lift :: Monad m => m a -> ReaderT i m a #
Monad m => Monad (ReaderT i m) #
Methods (>>=) :: ReaderT i m a -> (a -> ReaderT i m b) -> ReaderT i m b # (>>) :: ReaderT i m a -> ReaderT i m b -> ReaderT i m b # return :: a -> ReaderT i m a # fail :: String -> ReaderT i m a #
Monad m => Functor (ReaderT i m) #
Methods fmap :: (a -> b) -> ReaderT i m a -> ReaderT i m b # (<$) :: a -> ReaderT i m b -> ReaderT i m a #
MonadFix m => MonadFix (ReaderT i m) #
Methods mfix :: (a -> ReaderT i m a) -> ReaderT i m a #
Monad m => Applicative (ReaderT i m) #
Methods pure :: a -> ReaderT i m a # (<>) :: ReaderT i m (a -> b) -> ReaderT i m a -> ReaderT i m b # (>) :: ReaderT i m a -> ReaderT i m b -> ReaderT i m b # (<*) :: ReaderT i m a -> ReaderT i m b -> ReaderT i m a #
MonadPlus m => Alternative (ReaderT i m) #
Methods empty :: ReaderT i m a # (<\|>) :: ReaderT i m a -> ReaderT i m a -> ReaderT i m a # some :: ReaderT i m a -> ReaderT i m [a] # many :: ReaderT i m a -> ReaderT i m [a] #
MonadPlus m => MonadPlus (ReaderT i m) #
Methods mzero :: ReaderT i m a # mplus :: ReaderT i m a -> ReaderT i m a -> ReaderT i m a #
ContM m => ContM (ReaderT i m) #
Methods callWithCC :: ((a -> Label (ReaderT i m)) -> ReaderT i m a) -> ReaderT i m a #
AbortM m i => AbortM (ReaderT j m) i #
Methods abort :: i -> ReaderT j m a #
RunExceptionM m i => RunExceptionM (ReaderT j m) i #
Methods try :: ReaderT j m a -> ReaderT j m (Either i a) #
RunWriterM m j => RunWriterM (ReaderT i m) j #
Methods collect :: ReaderT i m a -> ReaderT i m (a, j) #
Monad m => RunReaderM (ReaderT i m) i #
Methods local :: i -> ReaderT i m a -> ReaderT i m a #
ExceptionM m j => ExceptionM (ReaderT i m) j #
Methods raise :: j -> ReaderT i m a #
StateM m j => StateM (ReaderT i m) j #
Methods get :: ReaderT i m j # set :: j -> ReaderT i m () #
WriterM m j => WriterM (ReaderT i m) j #
Methods put :: j -> ReaderT i m () #
Monad m => ReaderM (ReaderT i m) i #
Methods ask :: ReaderT i m i #
BaseM m n => BaseM (ReaderT i m) n #
Methods inBase :: n a -> ReaderT i m a #
RunM m a r => RunM (ReaderT i m) a (i -> r) #
Methods runM :: ReaderT i m a -> i -> r #

data WriterT i m a #

Add support for collecting values of type i. The type i should be a monoid, whose unit is used to represent a lack of a value, and whose binary operation is used to combine multiple values. This transformer is strict in its output component.

Instances

Monoid i => MonadT (WriterT i) #
Methods lift :: Monad m => m a -> WriterT i m a #
(Monad m, Monoid i) => Monad (WriterT i m) #
Methods (>>=) :: WriterT i m a -> (a -> WriterT i m b) -> WriterT i m b # (>>) :: WriterT i m a -> WriterT i m b -> WriterT i m b # return :: a -> WriterT i m a # fail :: String -> WriterT i m a #
(Monad m, Monoid i) => Functor (WriterT i m) #
Methods fmap :: (a -> b) -> WriterT i m a -> WriterT i m b # (<$) :: a -> WriterT i m b -> WriterT i m a #
(MonadFix m, Monoid i) => MonadFix (WriterT i m) #
Methods mfix :: (a -> WriterT i m a) -> WriterT i m a #
(Monad m, Monoid i) => Applicative (WriterT i m) #
Methods pure :: a -> WriterT i m a # (<>) :: WriterT i m (a -> b) -> WriterT i m a -> WriterT i m b # (>) :: WriterT i m a -> WriterT i m b -> WriterT i m b # (<*) :: WriterT i m a -> WriterT i m b -> WriterT i m a #
(MonadPlus m, Monoid i) => Alternative (WriterT i m) #
Methods empty :: WriterT i m a # (<\|>) :: WriterT i m a -> WriterT i m a -> WriterT i m a # some :: WriterT i m a -> WriterT i m [a] # many :: WriterT i m a -> WriterT i m [a] #
(MonadPlus m, Monoid i) => MonadPlus (WriterT i m) #
Methods mzero :: WriterT i m a # mplus :: WriterT i m a -> WriterT i m a -> WriterT i m a #
(ContM m, Monoid i) => ContM (WriterT i m) #
Methods callWithCC :: ((a -> Label (WriterT i m)) -> WriterT i m a) -> WriterT i m a #
(AbortM m i, Monoid j) => AbortM (WriterT j m) i #
Methods abort :: i -> WriterT j m a #
(RunExceptionM m i, Monoid j) => RunExceptionM (WriterT j m) i #
Methods try :: WriterT j m a -> WriterT j m (Either i a) #
(Monad m, Monoid i) => RunWriterM (WriterT i m) i #
Methods collect :: WriterT i m a -> WriterT i m (a, i) #
(RunReaderM m j, Monoid i) => RunReaderM (WriterT i m) j #
Methods local :: j -> WriterT i m a -> WriterT i m a #
(ExceptionM m j, Monoid i) => ExceptionM (WriterT i m) j #
Methods raise :: j -> WriterT i m a #
(StateM m j, Monoid i) => StateM (WriterT i m) j #
Methods get :: WriterT i m j # set :: j -> WriterT i m () #
(Monad m, Monoid i) => WriterM (WriterT i m) i #
Methods put :: i -> WriterT i m () #
(ReaderM m j, Monoid i) => ReaderM (WriterT i m) j #
Methods ask :: WriterT i m j #
(BaseM m n, Monoid i) => BaseM (WriterT i m) n #
Methods inBase :: n a -> WriterT i m a #
(Monoid i, RunM m (a, i) r) => RunM (WriterT i m) a r #
Methods runM :: WriterT i m a -> r #

data StateT i m a #

Add support for threading state of type i.

Instances

MonadT (StateT i) #
Methods lift :: Monad m => m a -> StateT i m a #
Monad m => Monad (StateT i m) #
Methods (>>=) :: StateT i m a -> (a -> StateT i m b) -> StateT i m b # (>>) :: StateT i m a -> StateT i m b -> StateT i m b # return :: a -> StateT i m a # fail :: String -> StateT i m a #
Monad m => Functor (StateT i m) #
Methods fmap :: (a -> b) -> StateT i m a -> StateT i m b # (<$) :: a -> StateT i m b -> StateT i m a #
MonadFix m => MonadFix (StateT i m) #
Methods mfix :: (a -> StateT i m a) -> StateT i m a #
Monad m => Applicative (StateT i m) #
Methods pure :: a -> StateT i m a # (<>) :: StateT i m (a -> b) -> StateT i m a -> StateT i m b # (>) :: StateT i m a -> StateT i m b -> StateT i m b # (<*) :: StateT i m a -> StateT i m b -> StateT i m a #
MonadPlus m => Alternative (StateT i m) #
Methods empty :: StateT i m a # (<\|>) :: StateT i m a -> StateT i m a -> StateT i m a # some :: StateT i m a -> StateT i m [a] # many :: StateT i m a -> StateT i m [a] #
MonadPlus m => MonadPlus (StateT i m) #
Methods mzero :: StateT i m a # mplus :: StateT i m a -> StateT i m a -> StateT i m a #
ContM m => ContM (StateT i m) #
Methods callWithCC :: ((a -> Label (StateT i m)) -> StateT i m a) -> StateT i m a #
AbortM m i => AbortM (StateT j m) i #
Methods abort :: i -> StateT j m a #
RunExceptionM m i => RunExceptionM (StateT j m) i #
Methods try :: StateT j m a -> StateT j m (Either i a) #
RunWriterM m j => RunWriterM (StateT i m) j #
Methods collect :: StateT i m a -> StateT i m (a, j) #
RunReaderM m j => RunReaderM (StateT i m) j #
Methods local :: j -> StateT i m a -> StateT i m a #
ExceptionM m j => ExceptionM (StateT i m) j #
Methods raise :: j -> StateT i m a #
Monad m => StateM (StateT i m) i #
Methods get :: StateT i m i # set :: i -> StateT i m () #
WriterM m j => WriterM (StateT i m) j #
Methods put :: j -> StateT i m () #
ReaderM m j => ReaderM (StateT i m) j #
Methods ask :: StateT i m j #
BaseM m n => BaseM (StateT i m) n #
Methods inBase :: n a -> StateT i m a #
RunM m (a, i) r => RunM (StateT i m) a (i -> r) #
Methods runM :: StateT i m a -> i -> r #

data ExceptionT i m a #

Add support for exceptions of type i.

Instances

MonadT (ExceptionT i) #
Methods lift :: Monad m => m a -> ExceptionT i m a #
Monad m => Monad (ExceptionT i m) #
Methods (>>=) :: ExceptionT i m a -> (a -> ExceptionT i m b) -> ExceptionT i m b # (>>) :: ExceptionT i m a -> ExceptionT i m b -> ExceptionT i m b # return :: a -> ExceptionT i m a # fail :: String -> ExceptionT i m a #
Monad m => Functor (ExceptionT i m) #
Methods fmap :: (a -> b) -> ExceptionT i m a -> ExceptionT i m b # (<$) :: a -> ExceptionT i m b -> ExceptionT i m a #
MonadFix m => MonadFix (ExceptionT i m) #
Methods mfix :: (a -> ExceptionT i m a) -> ExceptionT i m a #
Monad m => Applicative (ExceptionT i m) #
Methods pure :: a -> ExceptionT i m a # (<>) :: ExceptionT i m (a -> b) -> ExceptionT i m a -> ExceptionT i m b # (>) :: ExceptionT i m a -> ExceptionT i m b -> ExceptionT i m b # (<*) :: ExceptionT i m a -> ExceptionT i m b -> ExceptionT i m a #
MonadPlus m => Alternative (ExceptionT i m) #
Methods empty :: ExceptionT i m a # (<\|>) :: ExceptionT i m a -> ExceptionT i m a -> ExceptionT i m a # some :: ExceptionT i m a -> ExceptionT i m [a] # many :: ExceptionT i m a -> ExceptionT i m [a] #
MonadPlus m => MonadPlus (ExceptionT i m) #
Methods mzero :: ExceptionT i m a # mplus :: ExceptionT i m a -> ExceptionT i m a -> ExceptionT i m a #
ContM m => ContM (ExceptionT i m) #
Methods callWithCC :: ((a -> Label (ExceptionT i m)) -> ExceptionT i m a) -> ExceptionT i m a #
AbortM m i => AbortM (ExceptionT j m) i #
Methods abort :: i -> ExceptionT j m a #
Monad m => RunExceptionM (ExceptionT i m) i #
Methods try :: ExceptionT i m a -> ExceptionT i m (Either i a) #
RunWriterM m j => RunWriterM (ExceptionT i m) j #
Methods collect :: ExceptionT i m a -> ExceptionT i m (a, j) #
RunReaderM m j => RunReaderM (ExceptionT i m) j #
Methods local :: j -> ExceptionT i m a -> ExceptionT i m a #
Monad m => ExceptionM (ExceptionT i m) i #
Methods raise :: i -> ExceptionT i m a #
StateM m j => StateM (ExceptionT i m) j #
Methods get :: ExceptionT i m j # set :: j -> ExceptionT i m () #
WriterM m j => WriterM (ExceptionT i m) j #
Methods put :: j -> ExceptionT i m () #
ReaderM m j => ReaderM (ExceptionT i m) j #
Methods ask :: ExceptionT i m j #
BaseM m n => BaseM (ExceptionT i m) n #
Methods inBase :: n a -> ExceptionT i m a #
RunM m (Either i a) r => RunM (ExceptionT i m) a r #
Methods runM :: ExceptionT i m a -> r #

About the WriterM instance: If an exception is risen while we are collecting output, then the output is lost. If the output is important, then use try to ensure that no exception may occur. Example:

do (r,w) <- collect (try m)
   case r of
     Left err -> ...do something...
     Right a  -> ...do something...

data ChoiceT m a #

Add support for multiple answers.

Instances

MonadT ChoiceT #
Methods lift :: Monad m => m a -> ChoiceT m a #
Monad m => Monad (ChoiceT m) #
Methods (>>=) :: ChoiceT m a -> (a -> ChoiceT m b) -> ChoiceT m b # (>>) :: ChoiceT m a -> ChoiceT m b -> ChoiceT m b # return :: a -> ChoiceT m a # fail :: String -> ChoiceT m a #
Monad m => Functor (ChoiceT m) #
Methods fmap :: (a -> b) -> ChoiceT m a -> ChoiceT m b # (<$) :: a -> ChoiceT m b -> ChoiceT m a #
Monad m => Applicative (ChoiceT m) #
Methods pure :: a -> ChoiceT m a # (<>) :: ChoiceT m (a -> b) -> ChoiceT m a -> ChoiceT m b # (>) :: ChoiceT m a -> ChoiceT m b -> ChoiceT m b # (<*) :: ChoiceT m a -> ChoiceT m b -> ChoiceT m a #
Monad m => Alternative (ChoiceT m) #
Methods empty :: ChoiceT m a # (<\|>) :: ChoiceT m a -> ChoiceT m a -> ChoiceT m a # some :: ChoiceT m a -> ChoiceT m [a] # many :: ChoiceT m a -> ChoiceT m [a] #
Monad m => MonadPlus (ChoiceT m) #
Methods mzero :: ChoiceT m a # mplus :: ChoiceT m a -> ChoiceT m a -> ChoiceT m a #
ContM m => ContM (ChoiceT m) #
Methods callWithCC :: ((a -> Label (ChoiceT m)) -> ChoiceT m a) -> ChoiceT m a #
AbortM m i => AbortM (ChoiceT m) i #
Methods abort :: i -> ChoiceT m a #
ExceptionM m j => ExceptionM (ChoiceT m) j #
Methods raise :: j -> ChoiceT m a #
StateM m j => StateM (ChoiceT m) j #
Methods get :: ChoiceT m j # set :: j -> ChoiceT m () #
WriterM m j => WriterM (ChoiceT m) j #
Methods put :: j -> ChoiceT m () #
ReaderM m j => ReaderM (ChoiceT m) j #
Methods ask :: ChoiceT m j #
BaseM m n => BaseM (ChoiceT m) n #
Methods inBase :: n a -> ChoiceT m a #
RunM m (Maybe (a, ChoiceT m a)) r => RunM (ChoiceT m) a r #
Methods runM :: ChoiceT m a -> r #

data ContT i m a #

Add support for continuations within a prompt of type i.

Instances

MonadT (ContT i) #
Methods lift :: Monad m => m a -> ContT i m a #
Monad m => Monad (ContT i m) #
Methods (>>=) :: ContT i m a -> (a -> ContT i m b) -> ContT i m b # (>>) :: ContT i m a -> ContT i m b -> ContT i m b # return :: a -> ContT i m a # fail :: String -> ContT i m a #
Monad m => Functor (ContT i m) #
Methods fmap :: (a -> b) -> ContT i m a -> ContT i m b # (<$) :: a -> ContT i m b -> ContT i m a #
Monad m => Applicative (ContT i m) #
Methods pure :: a -> ContT i m a # (<>) :: ContT i m (a -> b) -> ContT i m a -> ContT i m b # (>) :: ContT i m a -> ContT i m b -> ContT i m b # (<*) :: ContT i m a -> ContT i m b -> ContT i m a #
MonadPlus m => Alternative (ContT i m) #
Methods empty :: ContT i m a # (<\|>) :: ContT i m a -> ContT i m a -> ContT i m a # some :: ContT i m a -> ContT i m [a] # many :: ContT i m a -> ContT i m [a] #
MonadPlus m => MonadPlus (ContT i m) #
Methods mzero :: ContT i m a # mplus :: ContT i m a -> ContT i m a -> ContT i m a #
Monad m => ContM (ContT i m) #
Methods callWithCC :: ((a -> Label (ContT i m)) -> ContT i m a) -> ContT i m a #
Monad m => AbortM (ContT i m) i #
Methods abort :: i -> ContT i m a #
(RunWriterM m j, MonadFix m) => RunWriterM (ContT i m) j #
Methods collect :: ContT i m a -> ContT i m (a, j) #
RunReaderM m j => RunReaderM (ContT i m) j #
Methods local :: j -> ContT i m a -> ContT i m a #
ExceptionM m j => ExceptionM (ContT i m) j #
Methods raise :: j -> ContT i m a #
StateM m j => StateM (ContT i m) j #
Methods get :: ContT i m j # set :: j -> ContT i m () #
WriterM m j => WriterM (ContT i m) j #
Methods put :: j -> ContT i m () #
ReaderM m j => ReaderM (ContT i m) j #
Methods ask :: ContT i m j #
BaseM m n => BaseM (ContT i m) n #
Methods inBase :: n a -> ContT i m a #
RunM m i r => RunM (ContT i m) a ((a -> m i) -> r) #
Methods runM :: ContT i m a -> (a -> m i) -> r #

Lifting

The following operations allow us to promote computations in the underlying monad to computations that support an extra effect. Computations defined in this way do not make use of the new effect but can be combined with other operations that utilize the effect.

class MonadT t where #

Minimal complete definition

lift

Methods

lift :: Monad m => m a -> t m a #

Promote a computation from the underlying monad.

Instances

MonadT ChoiceT #
Methods lift :: Monad m => m a -> ChoiceT m a #
MonadT IdT #
Methods lift :: Monad m => m a -> IdT m a #
MonadT (ContT i) #
Methods lift :: Monad m => m a -> ContT i m a #
MonadT (ExceptionT i) #
Methods lift :: Monad m => m a -> ExceptionT i m a #
MonadT (StateT i) #
Methods lift :: Monad m => m a -> StateT i m a #
Monoid i => MonadT (WriterT i) #
Methods lift :: Monad m => m a -> WriterT i m a #
MonadT (ReaderT i) #
Methods lift :: Monad m => m a -> ReaderT i m a #

class (Monad m, Monad n) => BaseM m n | m -> n where #

Minimal complete definition

inBase

Methods

inBase :: n a -> m a #

Promote a computation from the base monad.

Instances

BaseM [] [] #
Methods inBase :: [a] -> [a] #
BaseM Maybe Maybe #
Methods inBase :: Maybe a -> Maybe a #
BaseM IO IO #
Methods inBase :: IO a -> IO a #
BaseM Lift Lift #
Methods inBase :: Lift a -> Lift a #
BaseM Id Id #
Methods inBase :: Id a -> Id a #
BaseM m n => BaseM (ChoiceT m) n #
Methods inBase :: n a -> ChoiceT m a #
BaseM m n => BaseM (IdT m) n #
Methods inBase :: n a -> IdT m a #
BaseM (ST s) (ST s) #
Methods inBase :: ST s a -> ST s a #
BaseM (Cont i) (Cont i) #
Methods inBase :: Cont i a -> Cont i a #
BaseM (Exception i) (Exception i) #
Methods inBase :: Exception i a -> Exception i a #
BaseM (State i) (State i) #
Methods inBase :: State i a -> State i a #
Monoid i => BaseM (Writer i) (Writer i) #
Methods inBase :: Writer i a -> Writer i a #
BaseM (Reader i) (Reader i) #
Methods inBase :: Reader i a -> Reader i a #
BaseM m n => BaseM (ContT i m) n #
Methods inBase :: n a -> ContT i m a #
BaseM m n => BaseM (ExceptionT i m) n #
Methods inBase :: n a -> ExceptionT i m a #
BaseM m n => BaseM (StateT i m) n #
Methods inBase :: n a -> StateT i m a #
(BaseM m n, Monoid i) => BaseM (WriterT i m) n #
Methods inBase :: n a -> WriterT i m a #
BaseM m n => BaseM (ReaderT i m) n #
Methods inBase :: n a -> ReaderT i m a #

Effect Classes

The following classes define overloaded operations that can be used to define effectful computations.

class Monad m => ReaderM m i | m -> i where #

Classifies monads that provide access to a context of type i.

Minimal complete definition

ask

Methods

ask :: m i #

Get the context.

Instances

ReaderM m j => ReaderM (ChoiceT m) j #
Methods ask :: ChoiceT m j #
ReaderM m j => ReaderM (IdT m) j #
Methods ask :: IdT m j #
ReaderM (Reader i) i #
Methods ask :: Reader i i #
ReaderM m j => ReaderM (ContT i m) j #
Methods ask :: ContT i m j #
ReaderM m j => ReaderM (ExceptionT i m) j #
Methods ask :: ExceptionT i m j #
ReaderM m j => ReaderM (StateT i m) j #
Methods ask :: StateT i m j #
(ReaderM m j, Monoid i) => ReaderM (WriterT i m) j #
Methods ask :: WriterT i m j #
Monad m => ReaderM (ReaderT i m) i #
Methods ask :: ReaderT i m i #

class Monad m => WriterM m i | m -> i where #

Classifies monads that can collect values of type i.

Minimal complete definition

put

Methods

put :: i -> m () #

Add a value to the collection.

Instances

WriterM m j => WriterM (ChoiceT m) j #
Methods put :: j -> ChoiceT m () #
WriterM m j => WriterM (IdT m) j #
Methods put :: j -> IdT m () #
Monoid i => WriterM (Writer i) i #
Methods put :: i -> Writer i () #
WriterM m j => WriterM (ContT i m) j #
Methods put :: j -> ContT i m () #
WriterM m j => WriterM (ExceptionT i m) j #
Methods put :: j -> ExceptionT i m () #
WriterM m j => WriterM (StateT i m) j #
Methods put :: j -> StateT i m () #
(Monad m, Monoid i) => WriterM (WriterT i m) i #
Methods put :: i -> WriterT i m () #
WriterM m j => WriterM (ReaderT i m) j #
Methods put :: j -> ReaderT i m () #

class Monad m => StateM m i | m -> i where #

Classifies monads that propagate a state component of type i.

Minimal complete definition

get, set

Methods

get :: m i #

Get the state.

set :: i -> m () #

Set the state.

Instances

StateM m j => StateM (ChoiceT m) j #
Methods get :: ChoiceT m j # set :: j -> ChoiceT m () #
StateM m j => StateM (IdT m) j #
Methods get :: IdT m j # set :: j -> IdT m () #
StateM (State i) i #
Methods get :: State i i # set :: i -> State i () #
StateM m j => StateM (ContT i m) j #
Methods get :: ContT i m j # set :: j -> ContT i m () #
StateM m j => StateM (ExceptionT i m) j #
Methods get :: ExceptionT i m j # set :: j -> ExceptionT i m () #
Monad m => StateM (StateT i m) i #
Methods get :: StateT i m i # set :: i -> StateT i m () #
(StateM m j, Monoid i) => StateM (WriterT i m) j #
Methods get :: WriterT i m j # set :: j -> WriterT i m () #
StateM m j => StateM (ReaderT i m) j #
Methods get :: ReaderT i m j # set :: j -> ReaderT i m () #

class Monad m => ExceptionM m i | m -> i where #

Classifies monads that support raising exceptions of type i.

Minimal complete definition

raise

Methods

raise :: i -> m a #

Raise an exception.

Instances

ExceptionM IO SomeException #
Methods raise :: SomeException -> IO a #
ExceptionM m j => ExceptionM (ChoiceT m) j #
Methods raise :: j -> ChoiceT m a #
ExceptionM m j => ExceptionM (IdT m) j #
Methods raise :: j -> IdT m a #
ExceptionM (Exception i) i #
Methods raise :: i -> Exception i a #
ExceptionM m j => ExceptionM (ContT i m) j #
Methods raise :: j -> ContT i m a #
Monad m => ExceptionM (ExceptionT i m) i #
Methods raise :: i -> ExceptionT i m a #
ExceptionM m j => ExceptionM (StateT i m) j #
Methods raise :: j -> StateT i m a #
(ExceptionM m j, Monoid i) => ExceptionM (WriterT i m) j #
Methods raise :: j -> WriterT i m a #
ExceptionM m j => ExceptionM (ReaderT i m) j #
Methods raise :: j -> ReaderT i m a #

class Monad m => ContM m where #

Classifies monads that provide access to a computation's continuation.

Minimal complete definition

callWithCC

Methods

callWithCC :: ((a -> Label m) -> m a) -> m a #

Capture the current continuation.

Instances

ContM m => ContM (ChoiceT m) #
Methods callWithCC :: ((a -> Label (ChoiceT m)) -> ChoiceT m a) -> ChoiceT m a #
ContM m => ContM (IdT m) #
Methods callWithCC :: ((a -> Label (IdT m)) -> IdT m a) -> IdT m a #
ContM (Cont i) #
Methods callWithCC :: ((a -> Label (Cont i)) -> Cont i a) -> Cont i a #
Monad m => ContM (ContT i m) #
Methods callWithCC :: ((a -> Label (ContT i m)) -> ContT i m a) -> ContT i m a #
ContM m => ContM (ExceptionT i m) #
Methods callWithCC :: ((a -> Label (ExceptionT i m)) -> ExceptionT i m a) -> ExceptionT i m a #
ContM m => ContM (StateT i m) #
Methods callWithCC :: ((a -> Label (StateT i m)) -> StateT i m a) -> StateT i m a #
(ContM m, Monoid i) => ContM (WriterT i m) #
Methods callWithCC :: ((a -> Label (WriterT i m)) -> WriterT i m a) -> WriterT i m a #
ContM m => ContM (ReaderT i m) #
Methods callWithCC :: ((a -> Label (ReaderT i m)) -> ReaderT i m a) -> ReaderT i m a #

class Monad m => AbortM m i where #

Classifies monads that support aborting the program and returning a given final result of type i.

Minimal complete definition

abort

Methods

abort :: i -> m a #

Abort the program with the given value as final result.

Instances

AbortM IO ExitCode #
Methods abort :: ExitCode -> IO a #
AbortM m i => AbortM (ChoiceT m) i #
Methods abort :: i -> ChoiceT m a #
AbortM m i => AbortM (IdT m) i #
Methods abort :: i -> IdT m a #
Monad m => AbortM (ContT i m) i #
Methods abort :: i -> ContT i m a #
AbortM m i => AbortM (ExceptionT j m) i #
Methods abort :: i -> ExceptionT j m a #
AbortM m i => AbortM (StateT j m) i #
Methods abort :: i -> StateT j m a #
(AbortM m i, Monoid j) => AbortM (WriterT j m) i #
Methods abort :: i -> WriterT j m a #
AbortM m i => AbortM (ReaderT j m) i #
Methods abort :: i -> ReaderT j m a #

data Label m #

An explicit representation for monadic continuations.

labelCC :: ContM m => a -> m (a, a -> Label m) #

Capture the current continuation. This function is like return, except that it also captures the current continuation. Later, we can use jump to repeat the computation from this point onwards but with a possibly different value.

labelCC_ :: forall m. ContM m => m (Label m) #

Capture the current continuation. Later we can use jump to restart the program from this point.

jump :: Label m -> m a #

Restart a previously captured computation.

labelC :: (forall b. m b) -> Label m #

Label a given continuation.

callCC :: ContM m => ((a -> m b) -> m a) -> m a #

A version of callWithCC that avoids the need for an explicit use of the jump function.

Execution

Eliminating Effects

The following functions eliminate the outermost effect of a computation by translating a computation into an equivalent computation in the underlying monad. (The exceptions are Id and Lift which are not transformers but ordinary monads and so, their run operations simply eliminate the monad.)

runId :: Id a -> a #

Get the result of a pure computation.

runLift :: Lift a -> a #

Get the result of a pure strict computation.

runIdT :: IdT m a -> m a #

Remove an identity layer.

runReaderT :: i -> ReaderT i m a -> m a #

Execute a reader computation in the given context.

runWriterT :: Monad m => WriterT i m a -> m (a, i) #

Execute a writer computation. Returns the result and the collected output.

runStateT :: i -> StateT i m a -> m (a, i) #

Execute a stateful computation in the given initial state. The second component of the result is the final state.

runExceptionT :: ExceptionT i m a -> m (Either i a) #

Execute a computation with exceptions. Successful results are tagged with Right, exceptional results are tagged with Left.

runContT :: (a -> m i) -> ContT i m a -> m i #

Execute a computation with the given continuation.

runChoiceT :: Monad m => ChoiceT m a -> m (Maybe (a, ChoiceT m a)) #

Execute a computation that may return multiple answers. The resulting computation returns Nothing if no answers were found, or Just (answer,new_comp), where answer is an answer, and new_comp is a computation that may produce more answers. The search is depth-first and left-biased with respect to the mplus operation.

findOne :: Monad m => ChoiceT m a -> m (Maybe a) #

Execute a computation that may return multiple answers, returning at most one answer.

findAll :: Monad m => ChoiceT m a -> m [a] #

Execute a computation that may return multiple answers, collecting all possible answers.

class Monad m => RunM m a r | m a -> r where #

Generalized running.

Minimal complete definition

runM

Methods

runM :: m a -> r #

Instances

RunM Lift a a #
Methods runM :: Lift a -> a #
RunM Id a a #
Methods runM :: Id a -> a #
RunM IO a (IO a) #
Methods runM :: IO a -> IO a #
RunM m (Maybe (a, ChoiceT m a)) r => RunM (ChoiceT m) a r #
Methods runM :: ChoiceT m a -> r #
RunM m a r => RunM (IdT m) a r #
Methods runM :: IdT m a -> r #
RunM m (Either i a) r => RunM (ExceptionT i m) a r #
Methods runM :: ExceptionT i m a -> r #
(Monoid i, RunM m (a, i) r) => RunM (WriterT i m) a r #
Methods runM :: WriterT i m a -> r #
RunM m i r => RunM (ContT i m) a ((a -> m i) -> r) #
Methods runM :: ContT i m a -> (a -> m i) -> r #
RunM m (a, i) r => RunM (StateT i m) a (i -> r) #
Methods runM :: StateT i m a -> i -> r #
RunM m a r => RunM (ReaderT i m) a (i -> r) #
Methods runM :: ReaderT i m a -> i -> r #

Nested Execution

The following classes define operations that are overloaded versions of the run operations. Unlike the run operations, these functions do not change the type of the computation (i.e., they do not remove a layer). Instead, they perform the effects in a ``separate effect thread''.

class ReaderM m i => RunReaderM m i | m -> i where #

Classifies monads that support changing the context for a sub-computation.

Minimal complete definition

local

Methods

local :: i -> m a -> m a #

Change the context for the duration of a sub-computation.

Instances

RunReaderM m j => RunReaderM (IdT m) j #
Methods local :: j -> IdT m a -> IdT m a #
RunReaderM (Reader i) i #
Methods local :: i -> Reader i a -> Reader i a #
RunReaderM m j => RunReaderM (ContT i m) j #
Methods local :: j -> ContT i m a -> ContT i m a #
RunReaderM m j => RunReaderM (ExceptionT i m) j #
Methods local :: j -> ExceptionT i m a -> ExceptionT i m a #
RunReaderM m j => RunReaderM (StateT i m) j #
Methods local :: j -> StateT i m a -> StateT i m a #
(RunReaderM m j, Monoid i) => RunReaderM (WriterT i m) j #
Methods local :: j -> WriterT i m a -> WriterT i m a #
Monad m => RunReaderM (ReaderT i m) i #
Methods local :: i -> ReaderT i m a -> ReaderT i m a #

class WriterM m i => RunWriterM m i | m -> i where #

Classifies monads that support collecting the output of a sub-computation.

Minimal complete definition

collect

Methods

collect :: m a -> m (a, i) #

Collect the output from a sub-computation.

Instances

RunWriterM m j => RunWriterM (IdT m) j #
Methods collect :: IdT m a -> IdT m (a, j) #
Monoid i => RunWriterM (Writer i) i #
Methods collect :: Writer i a -> Writer i (a, i) #
(RunWriterM m j, MonadFix m) => RunWriterM (ContT i m) j #
Methods collect :: ContT i m a -> ContT i m (a, j) #
RunWriterM m j => RunWriterM (ExceptionT i m) j #
Methods collect :: ExceptionT i m a -> ExceptionT i m (a, j) #
RunWriterM m j => RunWriterM (StateT i m) j #
Methods collect :: StateT i m a -> StateT i m (a, j) #
(Monad m, Monoid i) => RunWriterM (WriterT i m) i #
Methods collect :: WriterT i m a -> WriterT i m (a, i) #
RunWriterM m j => RunWriterM (ReaderT i m) j #
Methods collect :: ReaderT i m a -> ReaderT i m (a, j) #

class ExceptionM m i => RunExceptionM m i | m -> i where #

Classifies monads that support handling of exceptions.

Minimal complete definition

try

Methods

try :: m a -> m (Either i a) #

Convert computations that may raise an exception into computations that do not raise exception but instead, yield a tagged results. Exceptions are tagged with Left, successful computations are tagged with Right.

Instances

RunExceptionM IO SomeException #
Methods try :: IO a -> IO (Either SomeException a) #
RunExceptionM m i => RunExceptionM (IdT m) i #
Methods try :: IdT m a -> IdT m (Either i a) #
RunExceptionM (Exception i) i #
Methods try :: Exception i a -> Exception i (Either i a) #
Monad m => RunExceptionM (ExceptionT i m) i #
Methods try :: ExceptionT i m a -> ExceptionT i m (Either i a) #
RunExceptionM m i => RunExceptionM (StateT j m) i #
Methods try :: StateT j m a -> StateT j m (Either i a) #
(RunExceptionM m i, Monoid j) => RunExceptionM (WriterT j m) i #
Methods try :: WriterT j m a -> WriterT j m (Either i a) #
RunExceptionM m i => RunExceptionM (ReaderT j m) i #
Methods try :: ReaderT j m a -> ReaderT j m (Either i a) #

Utility functions

asks :: ReaderM m r => (r -> a) -> m a #

Apply a function to the environment. Useful for accessing environmnt components.

puts :: WriterM m w => (a, w) -> m a #

Add content the output and return a result.

sets :: StateM m s => (s -> (a, s)) -> m a #

Update the state and return a result.

sets_ :: StateM m s => (s -> s) -> m () #

Updates the state with the given function.

raises :: ExceptionM m x => Either x a -> m a #

Either raise an exception or return a value. Left values signify the we should raise an exception, Right values indicate success.

mapReader :: RunReaderM m r => (r -> r) -> m a -> m a #

Modify the environment for the duration of a computation.

mapWriter :: RunWriterM m w => (w -> w) -> m a -> m a #

Modify the output of a computation.

mapException :: RunExceptionM m x => (x -> x) -> m a -> m a #

Modify the exception that was risen by a computation.

handle :: RunExceptionM m x => m a -> (x -> m a) -> m a #

Apply the given exception handler, if a computation raises an exception.

Miscellaneous

version :: (Int, Int, Int) #

The current version of the library.

module Control.Monad