runWriter -package:monad-logger

Unwrap a writer computation as a (result, output) pair. (The inverse of writer.)

Unwrap a writer computation as a (result, output) pair. (The inverse of writer.)

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

Encapsulation of a writer computation, providing the accumulated output. Typical usage in arrow notation:

proc p -> do
...
(result, output) <- (|runWriter cmd|)

Run a Writer effect and return the final value along with the final output.

Run a Writer effect with a Monoidal log, applying a continuation to the final log and result.

runWriter k (pure a) = k mempty a

runWriter k (tell w) = k w ()

runWriter k (listen (tell w)) = k w (w, ())

runWriter k (censor f (tell w)) = k (f w) ()

Run a Writer effect with a Monoidal log, producing the final log alongside the result value.

runWriter (tell w) = pure (w, ())

runWriter (pure a) = pure (mempty, a)

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

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

Unwrap a writer computation. (The inverse of writerT.)

Run WriterT in the base monad Since 1.0.11

Run WriterT in the base monad Since 1.0.11

Run WriterT in the base monad

A variant of runWriterTVar where an STM action is used instead of a TVar to commit tells.

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.

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

Run the Writer effect and return the final value along with the final output (via Effectful.Writer.Static.Local).

Run the Writer effect and return the final value along with the final output (via Effectful.Writer.Static.Shared).

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.

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