Bluefin.Writer

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)

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