Modulepolysemy-1.9.2.0Haskell2010

Polysemy.Writer

Contents

Effect
Actions
Interpretations
Interpretations for Other Effects

Synopsis

data Writer
value tell
value listen
value pass
value censor
value runWriter
value runLazyWriter
value runWriterAssocR
value runLazyWriterAssocR
value runWriterTVar
value writerToIOFinal
value writerToIOAssocRFinal
value writerToEndoWriter
value outputToWriter

Packagepolysemy-1.9.2.0
Exports14
LanguageHaskell2010
LicenceBSD-3-Clause
SourceWriter.hs

Effect

datadata Writer o (m :: Type -> Type) a where

Source#

An effect capable of emitting and intercepting messages.

Constructors

Tell :: o -> Writer o m ()
Write a message to the log.
Listen :: m a -> Writer o m a
Return the log produced by the higher-order action.
Pass :: m (o -> o, a) -> Writer o m a
Run the given action and apply the function it returns to the log.

Actions

valuetell :: Member (Writer o) r => o -> Sem r ()

Write a message to the log.

valuelisten :: Member (Writer o) r => Sem r a -> Sem r (o, a)

Return the log produced by the higher-order action.

valuepass :: Member (Writer o) r => Sem r (o -> o, a) -> Sem r a

Run the given action and apply the function it returns to the log.

valuecensor :: Member (Writer o) r => (o -> o) -> Sem r a -> Sem r a

Source#

Interpretations

valuerunWriter :: Monoid o => Sem (Writer o ': r) a -> Sem r (o, a)

Source#

Run a Writer effect in the style of WriterT (but without the nasty space leak!)

valuerunLazyWriter :: Monoid o => Sem (Writer o ': r) a -> Sem r (o, a)

Source#

Run a Writer effect in the style of WriterT lazily.

Warning: This inherits the nasty space leak issue of WriterT! Don't use this if you don't have to.

valuerunWriterAssocR :: Monoid o => Sem (Writer o ': r) a -> Sem r (o, a)

Source#

Like runWriter, but right-associates uses of <>.

This asymptotically improves performance if the time complexity of <> for the Monoid depends only on the size of the first argument.

You should always use this instead of runWriter if the monoid is a list, such as String.

valuerunLazyWriterAssocR :: Monoid o => Sem (Writer o ': r) a -> Sem r (o, a)

Source#

Like runLazyWriter, but right-associates uses of <>.

This asymptotically improves performance if the time complexity of <> for the Monoid depends only on the size of the first argument.

You should always use this instead of runLazyWriter if the monoid is a list, such as String.

Warning: This inherits the nasty space leak issue of WriterT! Don't use this if you don't have to.

valuerunWriterTVar

:: (Monoid o, Member (Final IO) r)
=> TVar o
-> Sem (Writer o ': r) a
-> Sem r a

Source#

Transform a Writer effect into atomic operations over a TVar through final IO.

valuewriterToIOFinal

:: (Monoid o, Member (Final IO) r)
=> Sem (Writer o ': r) a
-> Sem r (o, a)

Source#

Run a Writer effect by transforming it into atomic operations through final IO.

Internally, this simply creates a new TVar, passes it to runWriterTVar, and then returns the result and the final value of the TVar.

Beware: Effects that aren't interpreted in terms of IO will have local state semantics in regards to Writer effects interpreted this way. See Final.

valuewriterToIOAssocRFinal

:: (Monoid o, Member (Final IO) r)
=> Sem (Writer o ': r) a
-> Sem r (o, a)

Source#

Like writerToIOFinal. but right-associates uses of <>.

This asymptotically improves performance if the time complexity of <> for the Monoid depends only on the size of the first argument.

You should always use this instead of writerToIOFinal if the monoid is a list, such as String.

Beware: Effects that aren't interpreted in terms of IO will have local state semantics in regards to Writer effects interpreted this way. See Final.

valuewriterToEndoWriter

:: (Monoid o, Member (Writer (Endo o)) r)
=> Sem (Writer o ': r) a
-> Sem r a

Source#

Transform a Writer o effect into a Writer (Endo o) effect, right-associating all uses of <> for o.

This can be used together with raiseUnder in order to create -AssocR variants out of regular Writer interpreters.

Interpretations for Other Effects

valueoutputToWriter :: Member (Writer o) r => Sem (Output o ': r) a -> Sem r a

Source#

Transform an Output effect into a Writer effect.