Safe Haskell	None
Language	Haskell2010

Bluefin.Writer

Contents

Handle
Handlers
Effectful operations

Synopsis

data Writer w (e :: Effects)
runWriter :: forall w (es :: Effects) r. Monoid w => (forall (e :: Effects). Writer w e -> Eff (e :& es) r) -> Eff es (r, w)
execWriter :: forall w (es :: Effects) r. Monoid w => (forall (e :: Effects). Writer w e -> Eff (e :& es) r) -> Eff es w
tell :: forall (e :: Effects) (es :: Effects) w. e :> es => Writer w e -> w -> Eff es ()

Documentation

In most cases you'll probably prefer Stream to Writer, but Writer can still be useful in some cases, for example with Data.Monoid.Any to determine whether an event ever occurred.

Handle

data Writer w (e :: Effects) #

Instances

Instances details

e :> es => OneWayCoercible (Writer w e :: Type) (Writer w es :: Type)
Instance details Defined in Bluefin.Internal Methods oneWayCoercibleImpl :: OneWayCoercibleD (Writer w e) (Writer w es) #
Handle (Writer w)
Instance details Defined in Bluefin.Internal Methods handleImpl :: HandleD (Writer w) # mapHandle :: forall (e :: Effects) (es :: Effects). e :> es => Writer w e -> Writer w es #
(TypeError ('Text "Writer cannot be cloned. Perhaps you want an STM channel?") :: Constraint) => CloneableHandle (Writer w)
Instance details Defined in Bluefin.Internal.CloneableHandle Methods cloneableHandleImpl :: CloneableHandleD (Writer w) #

Handlers

runWriter #

Arguments

:: forall w (es :: Effects) r. Monoid w
=> (forall (e :: Effects). Writer w e -> Eff (e :& es) r)	͘
-> Eff es (r, w)

>>> getAny $ snd $ runPureEff $ runWriter $ \w -> do
      -- Non-empty list (the tell event does happen)
      for_ [1 .. 10] $ \_ -> tell w (Any True)
True

execWriter #

Arguments

:: forall w (es :: Effects) r. Monoid w
=> (forall (e :: Effects). Writer w e -> Eff (e :& es) r)	͘
-> Eff es w

>>> getAny $ runPureEff $ execWriter $ \w -> do
      -- Non-empty list (the tell event does happen)
      for_ [1 .. 10] $ \_ -> tell w (Any True)
True

>>> getAny $ runPureEff $ execWriter $ \w -> do
      -- Empty list (the tell event does not happen)
      for_ [] $ \_ -> tell w (Any True)
False

Effectful operations

tell #

Arguments

:: forall (e :: Effects) (es :: Effects) w. e :> es
=> Writer w e
-> w	͘
-> Eff es ()

>>> getAny $ runPureEff $ execWriter $ \w -> do
      -- Non-empty list (the tell event does happen)
      for_ [1 .. 10] $ \_ -> tell w (Any True)
True