ZIO.Trans

Documentation

newtype EIO e a

Corresponds to IO[E, A] in Scala

Constructors

EIO

Fields

• _unEIO :: ExceptT e UIO a

Instances

MonadError e (EIO e)

Defined in ZIO.Trans

Methods

throwError :: e -> EIO e a

catchError :: EIO e a -> (e -> EIO e a) -> EIO e a

Monad (EIO e)

Defined in ZIO.Trans

Methods

(>>=) :: EIO e a -> (a -> EIO e b) -> EIO e b

(>>) :: EIO e a -> EIO e b -> EIO e b

return :: a -> EIO e a

Functor (EIO e)

Defined in ZIO.Trans

Methods

fmap :: (a -> b) -> EIO e a -> EIO e b

(<$) :: a -> EIO e b -> EIO e a

MonadFix (EIO e)

Defined in ZIO.Trans

Methods

mfix :: (a -> EIO e a) -> EIO e a

Applicative (EIO e)

Defined in ZIO.Trans

Methods

pure :: a -> EIO e a

(<*>) :: EIO e (a -> b) -> EIO e a -> EIO e b

liftA2 :: (a -> b -> c) -> EIO e a -> EIO e b -> EIO e c

(*>) :: EIO e a -> EIO e b -> EIO e b

(<*) :: EIO e a -> EIO e b -> EIO e a

Unexceptional (EIO e)

Defined in ZIO.Trans

Methods

lift :: UIO a -> EIO e a

newtype ZIO r e a

Constructors

ZIO

Fields

• _unZIO :: ReaderT r (EIO e) a

Instances

MonadReader r (ZIO r e)

Defined in ZIO.Trans

Methods

ask :: ZIO r e r

local :: (r -> r) -> ZIO r e a -> ZIO r e a

reader :: (r -> a) -> ZIO r e a

MonadError e (ZIO r e)

Defined in ZIO.Trans

Methods

throwError :: e -> ZIO r e a

catchError :: ZIO r e a -> (e -> ZIO r e a) -> ZIO r e a

Monad (ZIO r e)

Defined in ZIO.Trans

Methods

(>>=) :: ZIO r e a -> (a -> ZIO r e b) -> ZIO r e b

(>>) :: ZIO r e a -> ZIO r e b -> ZIO r e b

return :: a -> ZIO r e a

Functor (ZIO r e)

Defined in ZIO.Trans

Methods

fmap :: (a -> b) -> ZIO r e a -> ZIO r e b

(<$) :: a -> ZIO r e b -> ZIO r e a

MonadFix (ZIO r e)

Defined in ZIO.Trans

Methods

mfix :: (a -> ZIO r e a) -> ZIO r e a

Applicative (ZIO r e)

Defined in ZIO.Trans

Methods

pure :: a -> ZIO r e a

(<*>) :: ZIO r e (a -> b) -> ZIO r e a -> ZIO r e b

liftA2 :: (a -> b -> c) -> ZIO r e a -> ZIO r e b -> ZIO r e c

(*>) :: ZIO r e a -> ZIO r e b -> ZIO r e b

(<*) :: ZIO r e a -> ZIO r e b -> ZIO r e a

Unexceptional (ZIO r e)

Defined in ZIO.Trans

Methods

lift :: UIO a -> ZIO r e a

type UEIO a = EIO Void a

type URIO r a = ZIO r Void a

type UZIO a = ZIO Void Void a

type Task a = ZIO Void SomeNonPseudoException a

type RIO r a = ZIO r SomeNonPseudoException a

elift :: IO a -> EIO SomeNonPseudoException a

ezlift :: forall r e a. EIO e a -> ZIO r e a

zlift :: IO a -> ZIO r SomeNonPseudoException a

uelift :: forall e a. UIO a -> EIO e a

uzlift :: forall r e a. UIO a -> ZIO r e a

euUnlift :: UEIO a -> UIO a

zuUnlift :: UZIO a -> UIO a

mapEError :: (e -> e') -> EIO e a -> EIO e' a

mapZError :: (e -> e') -> ZIO r e a -> ZIO r e' a

runEIO :: MonadIO m => EIO e a -> (e -> m a) -> m a

runZIO :: MonadIO m => ZIO r e a -> r -> (e -> m a) -> m a

withEIO :: (e -> e') -> EIO e a -> EIO e' a

withZIO :: r -> (e -> e') -> ZIO r e a -> ZIO r e' a

module Control.Monad.Except

guard :: Alternative f => Bool -> f ()

Conditional failure of Alternative computations. Defined by

guard True  = pure ()
guard False = empty

Examples

Common uses of guard include conditionally signaling an error in an error monad and conditionally rejecting the current choice in an Alternative-based parser.

As an example of signaling an error in the error monad Maybe, consider a safe division function safeDiv x y that returns Nothing when the denominator y is zero and Just (x `div` y) otherwise. For example:

>>> safeDiv 4 0
Nothing
>>> safeDiv 4 2
Just 2

A definition of safeDiv using guards, but not guard:

safeDiv :: Int -> Int -> Maybe Int
safeDiv x y | y /= 0    = Just (x `div` y)
            | otherwise = Nothing

A definition of safeDiv using guard and Monad do-notation:

safeDiv :: Int -> Int -> Maybe Int
safeDiv x y = do
  guard (y /= 0)
  return (x `div` y)

join :: Monad m => m (m a) -> m a

The join function is the conventional monad join operator. It is used to remove one level of monadic structure, projecting its bound argument into the outer level.

'join bss' can be understood as the do expression

do bs <- bss
   bs

Examples

A common use of join is to run an IO computation returned from an STM transaction, since STM transactions can't perform IO directly. Recall that

atomically :: STM a -> IO a

is used to run STM transactions atomically. So, by specializing the types of atomically and join to

atomically :: STM (IO b) -> IO (IO b)
join       :: IO (IO b)  -> IO b

we can compose them as

join . atomically :: STM (IO b) -> IO b

to run an STM transaction and the IO action it returns.

class Applicative m => Monad (m :: Type -> Type) where

The Monad class defines the basic operations over a monad, a concept from a branch of mathematics known as category theory. From the perspective of a Haskell programmer, however, it is best to think of a monad as an abstract datatype of actions. Haskell's do expressions provide a convenient syntax for writing monadic expressions.

Instances of Monad should satisfy the following:

Left identity

return a >>= k = k a

Right identity

m >>= return = m

Associativity

m >>= (\x -> k x >>= h) = (m >>= k) >>= h

Furthermore, the Monad and Applicative operations should relate as follows:

• pure = return

• m1 <*> m2 = m1 >>= (x1 -> m2 >>= (x2 -> return (x1 x2)))

The above laws imply:

• fmap f xs  =  xs >>= return . f

• (>>) = (*>)

and that pure and (<*>) satisfy the applicative functor laws.

The instances of Monad for lists, Maybe and IO defined in the Prelude satisfy these laws.

Minimal complete definition

(>>=)

Methods

(>>=) :: m a -> (a -> m b) -> m b infixl 1

Sequentially compose two actions, passing any value produced by the first as an argument to the second.

'as >>= bs' can be understood as the do expression

do a <- as
   bs a

(>>) :: m a -> m b -> m b infixl 1

Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.

'as >> bs' can be understood as the do expression

do as
   bs

return :: a -> m a

Inject a value into the monadic type.

Instances

Monad []

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: [a] -> (a -> [b]) -> [b]

(>>) :: [a] -> [b] -> [b]

return :: a -> [a]

Monad Maybe

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: Maybe a -> (a -> Maybe b) -> Maybe b

(>>) :: Maybe a -> Maybe b -> Maybe b

return :: a -> Maybe a

Monad IO

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: IO a -> (a -> IO b) -> IO b

(>>) :: IO a -> IO b -> IO b

return :: a -> IO a

Monad Par1

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: Par1 a -> (a -> Par1 b) -> Par1 b

(>>) :: Par1 a -> Par1 b -> Par1 b

return :: a -> Par1 a

Monad Min

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Min a -> (a -> Min b) -> Min b

(>>) :: Min a -> Min b -> Min b

return :: a -> Min a

Monad Max

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Max a -> (a -> Max b) -> Max b

(>>) :: Max a -> Max b -> Max b

return :: a -> Max a

Monad First

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: First a -> (a -> First b) -> First b

(>>) :: First a -> First b -> First b

return :: a -> First a

Monad Last

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Last a -> (a -> Last b) -> Last b

(>>) :: Last a -> Last b -> Last b

return :: a -> Last a

Monad Option

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Option a -> (a -> Option b) -> Option b

(>>) :: Option a -> Option b -> Option b

return :: a -> Option a

Monad STM

Since: base-4.3.0.0

Defined in GHC.Conc.Sync

Methods

(>>=) :: STM a -> (a -> STM b) -> STM b

(>>) :: STM a -> STM b -> STM b

return :: a -> STM a

Monad ReadP

Since: base-2.1

Defined in Text.ParserCombinators.ReadP

Methods

(>>=) :: ReadP a -> (a -> ReadP b) -> ReadP b

(>>) :: ReadP a -> ReadP b -> ReadP b

return :: a -> ReadP a

Monad NonEmpty

Since: base-4.9.0.0

Defined in GHC.Base

Methods

(>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b

(>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b

return :: a -> NonEmpty a

Monad UIO

Defined in UnexceptionalIO

Methods

(>>=) :: UIO a -> (a -> UIO b) -> UIO b

(>>) :: UIO a -> UIO b -> UIO b

return :: a -> UIO a

Monad P

Since: base-2.1

Defined in Text.ParserCombinators.ReadP

Methods

(>>=) :: P a -> (a -> P b) -> P b

(>>) :: P a -> P b -> P b

return :: a -> P a

Monad (Either e)

Since: base-4.4.0.0

Defined in Data.Either

Methods

(>>=) :: Either e a -> (a -> Either e b) -> Either e b

(>>) :: Either e a -> Either e b -> Either e b

return :: a -> Either e a

Monad (U1 :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: U1 a -> (a -> U1 b) -> U1 b

(>>) :: U1 a -> U1 b -> U1 b

return :: a -> U1 a

Monoid a => Monad ((,) a)

Since: base-4.9.0.0

Defined in GHC.Base

Methods

(>>=) :: (a, a0) -> (a0 -> (a, b)) -> (a, b)

(>>) :: (a, a0) -> (a, b) -> (a, b)

return :: a0 -> (a, a0)

Monad (EIO e)

Defined in ZIO.Trans

Methods

(>>=) :: EIO e a -> (a -> EIO e b) -> EIO e b

(>>) :: EIO e a -> EIO e b -> EIO e b

return :: a -> EIO e a

Monad f => Monad (Rec1 f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: Rec1 f a -> (a -> Rec1 f b) -> Rec1 f b

(>>) :: Rec1 f a -> Rec1 f b -> Rec1 f b

return :: a -> Rec1 f a

(Monoid a, Monoid b) => Monad ((,,) a b)

Since: base-4.14.0.0

Defined in GHC.Base

Methods

(>>=) :: (a, b, a0) -> (a0 -> (a, b, b0)) -> (a, b, b0)

(>>) :: (a, b, a0) -> (a, b, b0) -> (a, b, b0)

return :: a0 -> (a, b, a0)

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

Defined in Control.Monad.Trans.Error

Methods

(>>=) :: ErrorT e m a -> (a -> ErrorT e m b) -> ErrorT e m b

(>>) :: ErrorT e m a -> ErrorT e m b -> ErrorT e m b

return :: a -> ErrorT e m a

Monad m => Monad (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

(>>=) :: ExceptT e m a -> (a -> ExceptT e m b) -> ExceptT e m b

(>>) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m b

return :: a -> ExceptT e m a

Monad m => Monad (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

(>>=) :: ReaderT r m a -> (a -> ReaderT r m b) -> ReaderT r m b

(>>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b

return :: a -> ReaderT r m a

Monad (ZIO r e)

Defined in ZIO.Trans

Methods

(>>=) :: ZIO r e a -> (a -> ZIO r e b) -> ZIO r e b

(>>) :: ZIO r e a -> ZIO r e b -> ZIO r e b

return :: a -> ZIO r e a

Monad ((->) r :: Type -> Type)

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: (r -> a) -> (a -> r -> b) -> r -> b

(>>) :: (r -> a) -> (r -> b) -> r -> b

return :: a -> r -> a

(Monad f, Monad g) => Monad (f :*: g)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: (f :*: g) a -> (a -> (f :*: g) b) -> (f :*: g) b

(>>) :: (f :*: g) a -> (f :*: g) b -> (f :*: g) b

return :: a -> (f :*: g) a

(Monoid a, Monoid b, Monoid c) => Monad ((,,,) a b c)

Since: base-4.14.0.0

Defined in GHC.Base

Methods

(>>=) :: (a, b, c, a0) -> (a0 -> (a, b, c, b0)) -> (a, b, c, b0)

(>>) :: (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, b0)

return :: a0 -> (a, b, c, a0)

(Monad f, Monad g) => Monad (Product f g)

Since: base-4.9.0.0

Defined in Data.Functor.Product

Methods

(>>=) :: Product f g a -> (a -> Product f g b) -> Product f g b

(>>) :: Product f g a -> Product f g b -> Product f g b

return :: a -> Product f g a

Monad f => Monad (M1 i c f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: M1 i c f a -> (a -> M1 i c f b) -> M1 i c f b

(>>) :: M1 i c f a -> M1 i c f b -> M1 i c f b

return :: a -> M1 i c f a

class Functor (f :: Type -> Type) where

A type f is a Functor if it provides a function fmap which, given any types a and b lets you apply any function from (a -> b) to turn an f a into an f b, preserving the structure of f. Furthermore f needs to adhere to the following:

Identity

fmap id == id

Composition

fmap (f . g) == fmap f . fmap g

Note, that the second law follows from the free theorem of the type fmap and the first law, so you need only check that the former condition holds.

Minimal complete definition

fmap

Methods

fmap :: (a -> b) -> f a -> f b

Using ApplicativeDo: 'fmap f as' can be understood as the do expression

do a <- as
   pure (f a)

with an inferred Functor constraint.

(<$) :: a -> f b -> f a infixl 4

Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

Using ApplicativeDo: 'a <$ bs' can be understood as the do expression

do bs
   pure a

with an inferred Functor constraint.

Instances

Functor []

Since: base-2.1

Defined in GHC.Base

Methods

fmap :: (a -> b) -> [a] -> [b]

(<$) :: a -> [b] -> [a]

Functor Maybe

Since: base-2.1

Defined in GHC.Base

Methods

fmap :: (a -> b) -> Maybe a -> Maybe b

(<$) :: a -> Maybe b -> Maybe a

Functor IO

Since: base-2.1

Defined in GHC.Base

Methods

fmap :: (a -> b) -> IO a -> IO b

(<$) :: a -> IO b -> IO a

Functor Par1

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> Par1 a -> Par1 b

(<$) :: a -> Par1 b -> Par1 a

Functor Min

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> Min a -> Min b

(<$) :: a -> Min b -> Min a

Functor Max

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> Max a -> Max b

(<$) :: a -> Max b -> Max a

Functor First

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> First a -> First b

(<$) :: a -> First b -> First a

Functor Last

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> Last a -> Last b

(<$) :: a -> Last b -> Last a

Functor Option

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> Option a -> Option b

(<$) :: a -> Option b -> Option a

Functor Handler

Since: base-4.6.0.0

Defined in Control.Exception

Methods

fmap :: (a -> b) -> Handler a -> Handler b

(<$) :: a -> Handler b -> Handler a

Functor STM

Since: base-4.3.0.0

Defined in GHC.Conc.Sync

Methods

fmap :: (a -> b) -> STM a -> STM b

(<$) :: a -> STM b -> STM a

Functor ReadP

Since: base-2.1

Defined in Text.ParserCombinators.ReadP

Methods

fmap :: (a -> b) -> ReadP a -> ReadP b

(<$) :: a -> ReadP b -> ReadP a

Functor NonEmpty

Since: base-4.9.0.0

Defined in GHC.Base

Methods

fmap :: (a -> b) -> NonEmpty a -> NonEmpty b

(<$) :: a -> NonEmpty b -> NonEmpty a

Functor UIO

Defined in UnexceptionalIO

Methods

fmap :: (a -> b) -> UIO a -> UIO b

(<$) :: a -> UIO b -> UIO a

Functor P

Since: base-4.8.0.0

Defined in Text.ParserCombinators.ReadP

Methods

fmap :: (a -> b) -> P a -> P b

(<$) :: a -> P b -> P a

Functor (Either a)

Since: base-3.0

Defined in Data.Either

Methods

fmap :: (a0 -> b) -> Either a a0 -> Either a b

(<$) :: a0 -> Either a b -> Either a a0

Functor (V1 :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> V1 a -> V1 b

(<$) :: a -> V1 b -> V1 a

Functor (U1 :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> U1 a -> U1 b

(<$) :: a -> U1 b -> U1 a

Functor ((,) a)

Since: base-2.1

Defined in GHC.Base

Methods

fmap :: (a0 -> b) -> (a, a0) -> (a, b)

(<$) :: a0 -> (a, b) -> (a, a0)

Functor (Arg a)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

fmap :: (a0 -> b) -> Arg a a0 -> Arg a b

(<$) :: a0 -> Arg a b -> Arg a a0

Functor (EIO e)

Defined in ZIO.Trans

Methods

fmap :: (a -> b) -> EIO e a -> EIO e b

(<$) :: a -> EIO e b -> EIO e a

Functor f => Functor (Rec1 f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> Rec1 f a -> Rec1 f b

(<$) :: a -> Rec1 f b -> Rec1 f a

Functor (URec Char :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Char a -> URec Char b

(<$) :: a -> URec Char b -> URec Char a

Functor (URec Double :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Double a -> URec Double b

(<$) :: a -> URec Double b -> URec Double a

Functor (URec Float :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Float a -> URec Float b

(<$) :: a -> URec Float b -> URec Float a

Functor (URec Int :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Int a -> URec Int b

(<$) :: a -> URec Int b -> URec Int a

Functor (URec Word :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Word a -> URec Word b

(<$) :: a -> URec Word b -> URec Word a

Functor (URec (Ptr ()) :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec (Ptr ()) a -> URec (Ptr ()) b

(<$) :: a -> URec (Ptr ()) b -> URec (Ptr ()) a

Functor ((,,) a b)

Since: base-4.14.0.0

Defined in GHC.Base

Methods

fmap :: (a0 -> b0) -> (a, b, a0) -> (a, b, b0)

(<$) :: a0 -> (a, b, b0) -> (a, b, a0)

Functor m => Functor (ErrorT e m)

Defined in Control.Monad.Trans.Error

Methods

fmap :: (a -> b) -> ErrorT e m a -> ErrorT e m b

(<$) :: a -> ErrorT e m b -> ErrorT e m a

Functor m => Functor (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

fmap :: (a -> b) -> ExceptT e m a -> ExceptT e m b

(<$) :: a -> ExceptT e m b -> ExceptT e m a

Functor m => Functor (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

fmap :: (a -> b) -> ReaderT r m a -> ReaderT r m b

(<$) :: a -> ReaderT r m b -> ReaderT r m a

Functor (ZIO r e)

Defined in ZIO.Trans

Methods

fmap :: (a -> b) -> ZIO r e a -> ZIO r e b

(<$) :: a -> ZIO r e b -> ZIO r e a

Functor ((->) r :: Type -> Type)

Since: base-2.1

Defined in GHC.Base

Methods

fmap :: (a -> b) -> (r -> a) -> r -> b

(<$) :: a -> (r -> b) -> r -> a

Functor (K1 i c :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> K1 i c a -> K1 i c b

(<$) :: a -> K1 i c b -> K1 i c a

(Functor f, Functor g) => Functor (f :+: g)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> (f :+: g) a -> (f :+: g) b

(<$) :: a -> (f :+: g) b -> (f :+: g) a

(Functor f, Functor g) => Functor (f :*: g)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> (f :*: g) a -> (f :*: g) b

(<$) :: a -> (f :*: g) b -> (f :*: g) a

Functor ((,,,) a b c)

Since: base-4.14.0.0

Defined in GHC.Base

Methods

fmap :: (a0 -> b0) -> (a, b, c, a0) -> (a, b, c, b0)

(<$) :: a0 -> (a, b, c, b0) -> (a, b, c, a0)

(Functor f, Functor g) => Functor (Product f g)

Since: base-4.9.0.0

Defined in Data.Functor.Product

Methods

fmap :: (a -> b) -> Product f g a -> Product f g b

(<$) :: a -> Product f g b -> Product f g a

(Functor f, Functor g) => Functor (Sum f g)

Since: base-4.9.0.0

Defined in Data.Functor.Sum

Methods

fmap :: (a -> b) -> Sum f g a -> Sum f g b

(<$) :: a -> Sum f g b -> Sum f g a

Functor f => Functor (M1 i c f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> M1 i c f a -> M1 i c f b

(<$) :: a -> M1 i c f b -> M1 i c f a

(Functor f, Functor g) => Functor (f :.: g)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> (f :.: g) a -> (f :.: g) b

(<$) :: a -> (f :.: g) b -> (f :.: g) a

(Functor f, Functor g) => Functor (Compose f g)

Since: base-4.9.0.0

Defined in Data.Functor.Compose

Methods

fmap :: (a -> b) -> Compose f g a -> Compose f g b

(<$) :: a -> Compose f g b -> Compose f g a

class Monad m => MonadFix (m :: Type -> Type) where

Monads having fixed points with a 'knot-tying' semantics. Instances of MonadFix should satisfy the following laws:

Purity

mfix (return . h) = return (fix h)

Left shrinking (or Tightening)

mfix (\x -> a >>= \y -> f x y) = a >>= \y -> mfix (\x -> f x y)

Sliding

mfix (liftM h . f) = liftM h (mfix (f . h)), for strict h.

Nesting

mfix (\x -> mfix (\y -> f x y)) = mfix (\x -> f x x)

This class is used in the translation of the recursive do notation supported by GHC and Hugs.

Methods

mfix :: (a -> m a) -> m a

The fixed point of a monadic computation. mfix f executes the action f only once, with the eventual output fed back as the input. Hence f should not be strict, for then mfix f would diverge.

Instances

MonadFix []

Since: base-2.1

Defined in Control.Monad.Fix

Methods

mfix :: (a -> [a]) -> [a]

MonadFix Maybe

Since: base-2.1

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Maybe a) -> Maybe a

MonadFix IO

Since: base-2.1

Defined in Control.Monad.Fix

Methods

mfix :: (a -> IO a) -> IO a

MonadFix Par1

Since: base-4.9.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Par1 a) -> Par1 a

MonadFix Min

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

mfix :: (a -> Min a) -> Min a

MonadFix Max

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

mfix :: (a -> Max a) -> Max a

MonadFix First

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

mfix :: (a -> First a) -> First a

MonadFix Last

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

mfix :: (a -> Last a) -> Last a

MonadFix Option

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

mfix :: (a -> Option a) -> Option a

MonadFix First

Since: base-4.8.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> First a) -> First a

MonadFix Last

Since: base-4.8.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Last a) -> Last a

MonadFix Dual

Since: base-4.8.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Dual a) -> Dual a

MonadFix Sum

Since: base-4.8.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Sum a) -> Sum a

MonadFix Product

Since: base-4.8.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Product a) -> Product a

MonadFix Down

Since: base-4.12.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Down a) -> Down a

MonadFix NonEmpty

Since: base-4.9.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> NonEmpty a) -> NonEmpty a

MonadFix UIO

Defined in UnexceptionalIO

Methods

mfix :: (a -> UIO a) -> UIO a

MonadFix (Either e)

Since: base-4.3.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Either e a) -> Either e a

MonadFix (ST s)

Since: base-2.1

Defined in Control.Monad.Fix

Methods

mfix :: (a -> ST s a) -> ST s a

MonadFix (EIO e)

Defined in ZIO.Trans

Methods

mfix :: (a -> EIO e a) -> EIO e a

MonadFix f => MonadFix (Rec1 f)

Since: base-4.9.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Rec1 f a) -> Rec1 f a

MonadFix f => MonadFix (Ap f)

Since: base-4.12.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Ap f a) -> Ap f a

MonadFix f => MonadFix (Alt f)

Since: base-4.8.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Alt f a) -> Alt f a

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

Defined in Control.Monad.Trans.Error

Methods

mfix :: (a -> ErrorT e m a) -> ErrorT e m a

MonadFix m => MonadFix (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

mfix :: (a -> ExceptT e m a) -> ExceptT e m a

MonadFix m => MonadFix (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mfix :: (a -> ReaderT r m a) -> ReaderT r m a

MonadFix (ZIO r e)

Defined in ZIO.Trans

Methods

mfix :: (a -> ZIO r e a) -> ZIO r e a

MonadFix ((->) r :: Type -> Type)

Since: base-2.1

Defined in Control.Monad.Fix

Methods

mfix :: (a -> r -> a) -> r -> a

(MonadFix f, MonadFix g) => MonadFix (f :*: g)

Since: base-4.9.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> (f :*: g) a) -> (f :*: g) a

(MonadFix f, MonadFix g) => MonadFix (Product f g)

Since: base-4.9.0.0

Defined in Data.Functor.Product

Methods

mfix :: (a -> Product f g a) -> Product f g a

MonadFix f => MonadFix (M1 i c f)

Since: base-4.9.0.0

Defined in Control.Monad.Fix

Methods

mfix :: (a -> M1 i c f a) -> M1 i c f a

class Monad m => MonadFail (m :: Type -> Type) where

When a value is bound in do-notation, the pattern on the left hand side of <- might not match. In this case, this class provides a function to recover.

A Monad without a MonadFail instance may only be used in conjunction with pattern that always match, such as newtypes, tuples, data types with only a single data constructor, and irrefutable patterns (~pat).

Instances of MonadFail should satisfy the following law: fail s should be a left zero for >>=,

fail s >>= f  =  fail s

If your Monad is also MonadPlus, a popular definition is

fail _ = mzero

Since: base-4.9.0.0

Methods

fail :: String -> m a

Instances

MonadFail []

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> [a]

MonadFail Maybe

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> Maybe a

MonadFail IO

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> IO a

MonadFail ReadP

Since: base-4.9.0.0

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> ReadP a

MonadFail P

Since: base-4.9.0.0

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> P a

(Monad m, Error e) => MonadFail (ErrorT e m)

Defined in Control.Monad.Trans.Error

Methods

fail :: String -> ErrorT e m a

MonadFail m => MonadFail (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

fail :: String -> ExceptT e m a

MonadFail m => MonadFail (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

fail :: String -> ReaderT r m a

mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b)

Map each element of a structure to a monadic action, evaluate these actions from left to right, and collect the results. For a version that ignores the results see mapM_.

sequence :: (Traversable t, Monad m) => t (m a) -> m (t a)

Evaluate each monadic action in the structure from left to right, and collect the results. For a version that ignores the results see sequence_.

class Monad m => MonadIO (m :: Type -> Type) where

Monads in which IO computations may be embedded. Any monad built by applying a sequence of monad transformers to the IO monad will be an instance of this class.

Instances should satisfy the following laws, which state that liftIO is a transformer of monads:

• liftIO . return = return

• liftIO (m >>= f) = liftIO m >>= (liftIO . f)

Methods

liftIO :: IO a -> m a

Lift a computation from the IO monad.

Instances

MonadIO IO

Since: base-4.9.0.0

Defined in Control.Monad.IO.Class

Methods

liftIO :: IO a -> IO a

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

Defined in Control.Monad.Trans.Error

Methods

liftIO :: IO a -> ErrorT e m a

MonadIO m => MonadIO (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

liftIO :: IO a -> ExceptT e m a

MonadIO m => MonadIO (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

liftIO :: IO a -> ReaderT r m a

mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a

Direct MonadPlus equivalent of filter.

Examples

The filter function is just mfilter specialized to the list monad:

filter = ( mfilter :: (a -> Bool) -> [a] -> [a] )

An example using mfilter with the Maybe monad:

>>> mfilter odd (Just 1)
Just 1
>>> mfilter odd (Just 2)
Nothing

(<$!>) :: Monad m => (a -> b) -> m a -> m b infixl 4

Strict version of <$>.

Since: base-4.8.0.0

unless :: Applicative f => Bool -> f () -> f ()

The reverse of when.

replicateM_ :: Applicative m => Int -> m a -> m ()

Like replicateM, but discards the result.

replicateM :: Applicative m => Int -> m a -> m [a]

replicateM n act performs the action n times, gathering the results.

Using ApplicativeDo: 'replicateM 5 as' can be understood as the do expression

do a1 <- as
   a2 <- as
   a3 <- as
   a4 <- as
   a5 <- as
   pure [a1,a2,a3,a4,a5]

Note the Applicative constraint.

foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m ()

Like foldM, but discards the result.

foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b

The foldM function is analogous to foldl, except that its result is encapsulated in a monad. Note that foldM works from left-to-right over the list arguments. This could be an issue where (>>) and the `folded function' are not commutative.

foldM f a1 [x1, x2, ..., xm]

==

do
  a2 <- f a1 x1
  a3 <- f a2 x2
  ...
  f am xm

If right-to-left evaluation is required, the input list should be reversed.

Note: foldM is the same as foldlM

zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m ()

zipWithM_ is the extension of zipWithM which ignores the final result.

zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c]

The zipWithM function generalizes zipWith to arbitrary applicative functors.

mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c])

The mapAndUnzipM function maps its first argument over a list, returning the result as a pair of lists. This function is mainly used with complicated data structures or a state monad.

forever :: Applicative f => f a -> f b

Repeat an action indefinitely.

Using ApplicativeDo: 'forever as' can be understood as the pseudo-do expression

do as
   as
   ..

with as repeating.

Examples

A common use of forever is to process input from network sockets, Handles, and channels (e.g. MVar and Chan).

For example, here is how we might implement an echo server, using forever both to listen for client connections on a network socket and to echo client input on client connection handles:

echoServer :: Socket -> IO ()
echoServer socket = forever $ do
  client <- accept socket
  forkFinally (echo client) (\_ -> hClose client)
  where
    echo :: Handle -> IO ()
    echo client = forever $
      hGetLine client >>= hPutStrLn client

(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c infixr 1

Right-to-left composition of Kleisli arrows. (>=>), with the arguments flipped.

Note how this operator resembles function composition (.):

(.)   ::            (b ->   c) -> (a ->   b) -> a ->   c
(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c

(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1

Left-to-right composition of Kleisli arrows.

'(bs >=> cs) a' can be understood as the do expression

do b <- bs a
   cs b

filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a]

This generalizes the list-based filter function.

forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)

forM is mapM with its arguments flipped. For a version that ignores the results see forM_.

msum :: (Foldable t, MonadPlus m) => t (m a) -> m a

The sum of a collection of actions, generalizing concat. As of base 4.8.0.0, msum is just asum, specialized to MonadPlus.

sequence_ :: (Foldable t, Monad m) => t (m a) -> m ()

Evaluate each monadic action in the structure from left to right, and ignore the results. For a version that doesn't ignore the results see sequence.

As of base 4.8.0.0, sequence_ is just sequenceA_, specialized to Monad.

forM_ :: (Foldable t, Monad m) => t a -> (a -> m b) -> m ()

forM_ is mapM_ with its arguments flipped. For a version that doesn't ignore the results see forM.

As of base 4.8.0.0, forM_ is just for_, specialized to Monad.

mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()

Map each element of a structure to a monadic action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see mapM.

As of base 4.8.0.0, mapM_ is just traverse_, specialized to Monad.

fix :: (a -> a) -> a

fix f is the least fixed point of the function f, i.e. the least defined x such that f x = x.

For example, we can write the factorial function using direct recursion as

>>> let fac n = if n <= 1 then 1 else n * fac (n-1) in fac 5
120

This uses the fact that Haskell’s let introduces recursive bindings. We can rewrite this definition using fix,

>>> fix (\rec n -> if n <= 1 then 1 else n * rec (n-1)) 5
120

Instead of making a recursive call, we introduce a dummy parameter rec; when used within fix, this parameter then refers to fix’s argument, hence the recursion is reintroduced.

void :: Functor f => f a -> f ()

void value discards or ignores the result of evaluation, such as the return value of an IO action.

Using ApplicativeDo: 'void as' can be understood as the do expression

do as
   pure ()

with an inferred Functor constraint.

Examples

Replace the contents of a Maybe Int with unit:

>>> void Nothing
Nothing
>>> void (Just 3)
Just ()

Replace the contents of an Either Int Int with unit, resulting in an Either Int ():

>>> void (Left 8675309)
Left 8675309
>>> void (Right 8675309)
Right ()

Replace every element of a list with unit:

>>> void [1,2,3]
[(),(),()]

Replace the second element of a pair with unit:

>>> void (1,2)
(1,())

Discard the result of an IO action:

>>> mapM print [1,2]
1
2
[(),()]
>>> void $ mapM print [1,2]
1
2

ap :: Monad m => m (a -> b) -> m a -> m b

In many situations, the liftM operations can be replaced by uses of ap, which promotes function application.

return f `ap` x1 `ap` ... `ap` xn

is equivalent to

liftMn f x1 x2 ... xn

liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r

Promote a function to a monad, scanning the monadic arguments from left to right (cf. liftM2).

liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r

Promote a function to a monad, scanning the monadic arguments from left to right (cf. liftM2).

liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r

Promote a function to a monad, scanning the monadic arguments from left to right (cf. liftM2).

liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r

Promote a function to a monad, scanning the monadic arguments from left to right. For example,

liftM2 (+) [0,1] [0,2] = [0,2,1,3]
liftM2 (+) (Just 1) Nothing = Nothing

liftM :: Monad m => (a1 -> r) -> m a1 -> m r

Promote a function to a monad.

when :: Applicative f => Bool -> f () -> f ()

Conditional execution of Applicative expressions. For example,

when debug (putStrLn "Debugging")

will output the string Debugging if the Boolean value debug is True, and otherwise do nothing.

(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1

Same as >>=, but with the arguments interchanged.

class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where

Monads that also support choice and failure.

Minimal complete definition

Nothing

Methods

mzero :: m a

The identity of mplus. It should also satisfy the equations

mzero >>= f  =  mzero
v >> mzero   =  mzero

The default definition is

mzero = empty

mplus :: m a -> m a -> m a

An associative operation. The default definition is

mplus = (<|>)

Instances

MonadPlus []

Since: base-2.1

Defined in GHC.Base

Methods

mzero :: [a]

mplus :: [a] -> [a] -> [a]

MonadPlus Maybe

Since: base-2.1

Defined in GHC.Base

Methods

mzero :: Maybe a

mplus :: Maybe a -> Maybe a -> Maybe a

MonadPlus IO

Since: base-4.9.0.0

Defined in GHC.Base

Methods

mzero :: IO a

mplus :: IO a -> IO a -> IO a

MonadPlus Option

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

mzero :: Option a

mplus :: Option a -> Option a -> Option a

MonadPlus STM

Since: base-4.3.0.0

Defined in GHC.Conc.Sync

Methods

mzero :: STM a

mplus :: STM a -> STM a -> STM a

MonadPlus ReadP

Since: base-2.1

Defined in Text.ParserCombinators.ReadP

Methods

mzero :: ReadP a

mplus :: ReadP a -> ReadP a -> ReadP a

MonadPlus P

Since: base-2.1

Defined in Text.ParserCombinators.ReadP

Methods

mzero :: P a

mplus :: P a -> P a -> P a

MonadPlus (U1 :: Type -> Type)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

mzero :: U1 a

mplus :: U1 a -> U1 a -> U1 a

MonadPlus f => MonadPlus (Rec1 f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

mzero :: Rec1 f a

mplus :: Rec1 f a -> Rec1 f a -> Rec1 f a

(Monad m, Error e) => MonadPlus (ErrorT e m)

Defined in Control.Monad.Trans.Error

Methods

mzero :: ErrorT e m a

mplus :: ErrorT e m a -> ErrorT e m a -> ErrorT e m a

(Monad m, Monoid e) => MonadPlus (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

mzero :: ExceptT e m a

mplus :: ExceptT e m a -> ExceptT e m a -> ExceptT e m a

MonadPlus m => MonadPlus (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mzero :: ReaderT r m a

mplus :: ReaderT r m a -> ReaderT r m a -> ReaderT r m a

(MonadPlus f, MonadPlus g) => MonadPlus (f :*: g)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

mzero :: (f :*: g) a

mplus :: (f :*: g) a -> (f :*: g) a -> (f :*: g) a

(MonadPlus f, MonadPlus g) => MonadPlus (Product f g)

Since: base-4.9.0.0

Defined in Data.Functor.Product

Methods

mzero :: Product f g a

mplus :: Product f g a -> Product f g a -> Product f g a

MonadPlus f => MonadPlus (M1 i c f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

mzero :: M1 i c f a

mplus :: M1 i c f a -> M1 i c f a -> M1 i c f a

class MonadTrans (t :: (Type -> Type) -> Type -> Type)

The class of monad transformers. Instances should satisfy the following laws, which state that lift is a monad transformation:

• lift . return = return

• lift (m >>= f) = lift m >>= (lift . f)

Minimal complete definition

lift

Instances

MonadTrans (ErrorT e)

Defined in Control.Monad.Trans.Error

Methods

lift :: Monad m => m a -> ErrorT e m a

MonadTrans (ExceptT e)

Defined in Control.Monad.Trans.Except

Methods

lift :: Monad m => m a -> ExceptT e m a

MonadTrans (ReaderT r)

Defined in Control.Monad.Trans.Reader

Methods

lift :: Monad m => m a -> ReaderT r m a

asks

Arguments

:: MonadReader r m

=> (r -> a)

The selector function to apply to the environment.

-> m a

Retrieves a function of the current environment.

class Monad m => MonadReader r (m :: Type -> Type) | m -> r where

See examples in Control.Monad.Reader. Note, the partially applied function type (->) r is a simple reader monad. See the instance declaration below.

Minimal complete definition

(ask | reader), local

Methods

ask :: m r

Retrieves the monad environment.

local

Arguments

:: (r -> r)

The function to modify the environment.

-> m a

Reader to run in the modified environment.

-> m a

Executes a computation in a modified environment.

reader

Arguments

:: (r -> a)

The selector function to apply to the environment.

-> m a

Retrieves a function of the current environment.

Instances

MonadReader r m => MonadReader r (MaybeT m)

Defined in Control.Monad.Reader.Class

Methods

ask :: MaybeT m r

local :: (r -> r) -> MaybeT m a -> MaybeT m a

reader :: (r -> a) -> MaybeT m a

MonadReader r m => MonadReader r (ListT m)

Defined in Control.Monad.Reader.Class

Methods

ask :: ListT m r

local :: (r -> r) -> ListT m a -> ListT m a

reader :: (r -> a) -> ListT m a

MonadReader r (ZIO r e)

Defined in ZIO.Trans

Methods

ask :: ZIO r e r

local :: (r -> r) -> ZIO r e a -> ZIO r e a

reader :: (r -> a) -> ZIO r e a

Monad m => MonadReader r (ReaderT r m)

Defined in Control.Monad.Reader.Class

Methods

ask :: ReaderT r m r

local :: (r -> r) -> ReaderT r m a -> ReaderT r m a

reader :: (r -> a) -> ReaderT r m a

(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)

Defined in Control.Monad.Reader.Class

Methods

ask :: WriterT w m r

local :: (r -> r) -> WriterT w m a -> WriterT w m a

reader :: (r -> a) -> WriterT w m a

(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)

Defined in Control.Monad.Reader.Class

Methods

ask :: WriterT w m r

local :: (r -> r) -> WriterT w m a -> WriterT w m a

reader :: (r -> a) -> WriterT w m a

MonadReader r m => MonadReader r (StateT s m)

Defined in Control.Monad.Reader.Class

Methods

ask :: StateT s m r

local :: (r -> r) -> StateT s m a -> StateT s m a

reader :: (r -> a) -> StateT s m a

MonadReader r m => MonadReader r (StateT s m)

Defined in Control.Monad.Reader.Class

Methods

ask :: StateT s m r

local :: (r -> r) -> StateT s m a -> StateT s m a

reader :: (r -> a) -> StateT s m a

MonadReader r m => MonadReader r (IdentityT m)

Defined in Control.Monad.Reader.Class

Methods

ask :: IdentityT m r

local :: (r -> r) -> IdentityT m a -> IdentityT m a

reader :: (r -> a) -> IdentityT m a

MonadReader r m => MonadReader r (ExceptT e m)

Since: mtl-2.2

Defined in Control.Monad.Reader.Class

Methods

ask :: ExceptT e m r

local :: (r -> r) -> ExceptT e m a -> ExceptT e m a

reader :: (r -> a) -> ExceptT e m a

(Error e, MonadReader r m) => MonadReader r (ErrorT e m)

Defined in Control.Monad.Reader.Class

Methods

ask :: ErrorT e m r

local :: (r -> r) -> ErrorT e m a -> ErrorT e m a

reader :: (r -> a) -> ErrorT e m a

MonadReader r ((->) r :: Type -> Type)

Defined in Control.Monad.Reader.Class

Methods

ask :: r -> r

local :: (r -> r) -> (r -> a) -> r -> a

reader :: (r -> a) -> r -> a

MonadReader r' m => MonadReader r' (ContT r m)

Defined in Control.Monad.Reader.Class

Methods

ask :: ContT r m r'

local :: (r' -> r') -> ContT r m a -> ContT r m a

reader :: (r' -> a) -> ContT r m a

(Monad m, Monoid w) => MonadReader r (RWST r w s m)

Defined in Control.Monad.Reader.Class

Methods

ask :: RWST r w s m r

local :: (r -> r) -> RWST r w s m a -> RWST r w s m a

reader :: (r -> a) -> RWST r w s m a

(Monad m, Monoid w) => MonadReader r (RWST r w s m)

Defined in Control.Monad.Reader.Class

Methods

ask :: RWST r w s m r

local :: (r -> r) -> RWST r w s m a -> RWST r w s m a

reader :: (r -> a) -> RWST r w s m a

newtype ReaderT r (m :: Type -> Type) a

The reader monad transformer, which adds a read-only environment to the given monad.

The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

Constructors

ReaderT

Fields

• runReaderT :: r -> m a

Instances

Monad m => MonadReader r (ReaderT r m)

Defined in Control.Monad.Reader.Class

Methods

ask :: ReaderT r m r

local :: (r -> r) -> ReaderT r m a -> ReaderT r m a

reader :: (r -> a) -> ReaderT r m a

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

Defined in Control.Monad.Error.Class

Methods

throwError :: e -> ReaderT r m a

catchError :: ReaderT r m a -> (e -> ReaderT r m a) -> ReaderT r m a

MonadTrans (ReaderT r)

Defined in Control.Monad.Trans.Reader

Methods

lift :: Monad m => m a -> ReaderT r m a

Monad m => Monad (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

(>>=) :: ReaderT r m a -> (a -> ReaderT r m b) -> ReaderT r m b

(>>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b

return :: a -> ReaderT r m a

Functor m => Functor (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

fmap :: (a -> b) -> ReaderT r m a -> ReaderT r m b

(<$) :: a -> ReaderT r m b -> ReaderT r m a

MonadFix m => MonadFix (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mfix :: (a -> ReaderT r m a) -> ReaderT r m a

MonadFail m => MonadFail (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

fail :: String -> ReaderT r m a

Applicative m => Applicative (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

pure :: a -> ReaderT r m a

(<*>) :: ReaderT r m (a -> b) -> ReaderT r m a -> ReaderT r m b

liftA2 :: (a -> b -> c) -> ReaderT r m a -> ReaderT r m b -> ReaderT r m c

(*>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b

(<*) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m a

Contravariant m => Contravariant (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

contramap :: (a -> b) -> ReaderT r m b -> ReaderT r m a

(>$) :: b -> ReaderT r m b -> ReaderT r m a

MonadZip m => MonadZip (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mzip :: ReaderT r m a -> ReaderT r m b -> ReaderT r m (a, b)

mzipWith :: (a -> b -> c) -> ReaderT r m a -> ReaderT r m b -> ReaderT r m c

munzip :: ReaderT r m (a, b) -> (ReaderT r m a, ReaderT r m b)

MonadIO m => MonadIO (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

liftIO :: IO a -> ReaderT r m a

Alternative m => Alternative (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

empty :: ReaderT r m a

(<|>) :: ReaderT r m a -> ReaderT r m a -> ReaderT r m a

some :: ReaderT r m a -> ReaderT r m [a]

many :: ReaderT r m a -> ReaderT r m [a]

MonadPlus m => MonadPlus (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mzero :: ReaderT r m a

mplus :: ReaderT r m a -> ReaderT r m a -> ReaderT r m a

type Reader r = ReaderT r Identity

The parameterizable reader monad.

Computations are functions of a shared environment.

The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

runReader

Arguments

:: Reader r a

A Reader to run.

-> r

An initial environment.

-> a

Runs a Reader and extracts the final value from it. (The inverse of reader.)

mapReader :: (a -> b) -> Reader r a -> Reader r b

Transform the value returned by a Reader.

• runReader (mapReader f m) = f . runReader m

withReader

Arguments

:: (r' -> r)

The function to modify the environment.

-> Reader r a

Computation to run in the modified environment.

-> Reader r' a

Execute a computation in a modified environment (a specialization of withReaderT).

• runReader (withReader f m) = runReader m . f

mapReaderT :: (m a -> n b) -> ReaderT r m a -> ReaderT r n b

Transform the computation inside a ReaderT.

• runReaderT (mapReaderT f m) = f . runReaderT m

withReaderT

Arguments

:: forall r' r (m :: Type -> Type) a. (r' -> r)

The function to modify the environment.

-> ReaderT r m a

Computation to run in the modified environment.

-> ReaderT r' m a

Execute a computation in a modified environment (a more general version of local).

• runReaderT (withReaderT f m) = runReaderT m . f

fork :: Unexceptional m => UIO () -> m ThreadId

Mirrors forkIO, but re-throws errors to the parent thread

• Ignores manual thread kills, since those are on purpose.
• Re-throws async exceptions (SomeAsyncException) as is.
• Re-throws ExitCode as is in an attempt to exit with the requested code.
• Wraps synchronous PseudoException in async ChildThreadError.

forkFinally :: Unexceptional m => UIO a -> (Either PseudoException a -> UIO ()) -> m ThreadId

Mirrors forkFinally, but since the body is UIO, the thread must terminate successfully or because of PseudoException

bracket :: Unexceptional m => UIO a -> (a -> UIO ()) -> (a -> UIO c) -> m c

When you're doing resource handling, PseudoException matters. You still need to use the bracket pattern to handle cleanup.

unsafeFromIO :: Unexceptional m => IO a -> m a

You promise there are no exceptions but PseudoException thrown by this IO action

runEitherIO :: Exception e => UIO (Either e a) -> IO a

Re-embed UIO and possible exception back into IO

fromIO'

Arguments

:: (Exception e, Unexceptional m)

=> (SomeNonPseudoException -> e)

Default if an unexpected exception occurs

-> IO a

-> m (Either e a)

Catch any e in an IO action, with a default mapping for unexpected cases

data PseudoException

Not everything handled by the exception system is a run-time error you can handle. This is the class of unrecoverable pseudo-exceptions.

Additionally, except for ExitCode any of these pseudo-exceptions you could never guarantee to have caught. Since they can come from anywhere at any time, we could never guarentee that UIO does not contain them.

Constructors

ProgrammerError ProgrammerError

Mistakes programmers make

ExternalError ExternalError

Errors thrown by the runtime

Exit ExitCode

Process exit requests

Instances

Show PseudoException

Defined in UnexceptionalIO

Methods

showsPrec :: Int -> PseudoException -> ShowS

show :: PseudoException -> String

showList :: [PseudoException] -> ShowS

Exception PseudoException

Defined in UnexceptionalIO

Methods

toException :: PseudoException -> SomeException

fromException :: SomeException -> Maybe PseudoException

displayException :: PseudoException -> String

data ProgrammerError

Pseudo-exceptions caused by a programming error

Partial functions, error, undefined, etc

Constructors

TypeError TypeError

ArithException ArithException

ArrayException ArrayException

AssertionFailed AssertionFailed

ErrorCall ErrorCall

NestedAtomically NestedAtomically

NoMethodError NoMethodError

PatternMatchFail PatternMatchFail

RecConError RecConError

RecSelError RecSelError

RecUpdError RecSelError

Instances

Show ProgrammerError

Defined in UnexceptionalIO

Methods

showsPrec :: Int -> ProgrammerError -> ShowS

show :: ProgrammerError -> String

showList :: [ProgrammerError] -> ShowS

Exception ProgrammerError

Defined in UnexceptionalIO

Methods

toException :: ProgrammerError -> SomeException

fromException :: SomeException -> Maybe ProgrammerError

displayException :: ProgrammerError -> String

data ExternalError

Pseudo-exceptions thrown by the runtime environment

Constructors

CompactionFailed CompactionFailed

FixIOException FixIOException

AsyncException SomeAsyncException

BlockedIndefinitelyOnSTM BlockedIndefinitelyOnSTM

BlockedIndefinitelyOnMVar BlockedIndefinitelyOnMVar

Deadlock Deadlock

NonTermination NonTermination

Instances

Show ExternalError

Defined in UnexceptionalIO

Methods

showsPrec :: Int -> ExternalError -> ShowS

show :: ExternalError -> String

showList :: [ExternalError] -> ShowS

Exception ExternalError

Defined in UnexceptionalIO

Methods

toException :: ExternalError -> SomeException

fromException :: SomeException -> Maybe ExternalError

displayException :: ExternalError -> String

data SomeNonPseudoException

Every SomeException but PseudoException

Instances

Show SomeNonPseudoException

Defined in UnexceptionalIO

Methods

showsPrec :: Int -> SomeNonPseudoException -> ShowS

show :: SomeNonPseudoException -> String

showList :: [SomeNonPseudoException] -> ShowS

Exception SomeNonPseudoException

Defined in UnexceptionalIO

Methods

toException :: SomeNonPseudoException -> SomeException

fromException :: SomeException -> Maybe SomeNonPseudoException

displayException :: SomeNonPseudoException -> String

data UIO a

Like IO, but throws only PseudoException

Instances

Monad UIO

Defined in UnexceptionalIO

Methods

(>>=) :: UIO a -> (a -> UIO b) -> UIO b

(>>) :: UIO a -> UIO b -> UIO b

return :: a -> UIO a

Functor UIO

Defined in UnexceptionalIO

Methods

fmap :: (a -> b) -> UIO a -> UIO b

(<$) :: a -> UIO b -> UIO a

MonadFix UIO

Defined in UnexceptionalIO

Methods

mfix :: (a -> UIO a) -> UIO a

Applicative UIO

Defined in UnexceptionalIO

Methods

pure :: a -> UIO a

(<*>) :: UIO (a -> b) -> UIO a -> UIO b

liftA2 :: (a -> b -> c) -> UIO a -> UIO b -> UIO c

(*>) :: UIO a -> UIO b -> UIO b

(<*) :: UIO a -> UIO b -> UIO a

Unexceptional UIO

Defined in UnexceptionalIO

Methods

lift :: UIO a -> UIO a

class Monad m => Unexceptional (m :: Type -> Type)

Monads in which UIO computations may be embedded

Minimal complete definition

lift

Instances

Unexceptional IO

Defined in UnexceptionalIO

Methods

lift :: UIO a -> IO a

Unexceptional UIO

Defined in UnexceptionalIO

Methods

lift :: UIO a -> UIO a

Unexceptional (EIO e)

Defined in ZIO.Trans

Methods

lift :: UIO a -> EIO e a

Unexceptional (ZIO r e)

Defined in ZIO.Trans

Methods

lift :: UIO a -> ZIO r e a

newtype ChildThreadError

Async signal that a child thread ended due to non-async PseudoException

Constructors

ChildThreadError PseudoException

Instances

Show ChildThreadError

Defined in UnexceptionalIO

Methods

showsPrec :: Int -> ChildThreadError -> ShowS

show :: ChildThreadError -> String

showList :: [ChildThreadError] -> ShowS

Exception ChildThreadError

Defined in UnexceptionalIO

Methods

toException :: ChildThreadError -> SomeException

fromException :: SomeException -> Maybe ChildThreadError

displayException :: ChildThreadError -> String

data UIO a

Like IO, but throws only PseudoException

Instances

Monad UIO

Defined in UnexceptionalIO

Methods

(>>=) :: UIO a -> (a -> UIO b) -> UIO b

(>>) :: UIO a -> UIO b -> UIO b

return :: a -> UIO a

Functor UIO

Defined in UnexceptionalIO

Methods

fmap :: (a -> b) -> UIO a -> UIO b

(<$) :: a -> UIO b -> UIO a

MonadFix UIO

Defined in UnexceptionalIO

Methods

mfix :: (a -> UIO a) -> UIO a

Applicative UIO

Defined in UnexceptionalIO

Methods

pure :: a -> UIO a

(<*>) :: UIO (a -> b) -> UIO a -> UIO b

liftA2 :: (a -> b -> c) -> UIO a -> UIO b -> UIO c

(*>) :: UIO a -> UIO b -> UIO b

(<*) :: UIO a -> UIO b -> UIO a

Unexceptional UIO

Defined in UnexceptionalIO

Methods

lift :: UIO a -> UIO a

run :: MonadIO m => UIO a -> m a

Re-embed UIO into MonadIO

fromIO :: forall (m :: Type -> Type) a. Unexceptional m => IO a -> ExceptT SomeNonPseudoException m a

Catch any exception but PseudoException in an IO action