Control.Monad.Freer.Writer

Writer effects, for writing/appending values (line count, list of messages, etc.) to an output. Current value of Writer effect output is not accessible to the computation.

Using http://okmij.org/ftp/Haskell/extensible/Eff1.hs as a starting point.

Documentation

data Writer w r where

Writer effects - send outputs to an effect environment.

Constructors

Tell :: w -> Writer w ()

tell :: forall w effs. Member (Writer w) effs => w -> Eff effs ()

Send a change to the attached environment.

runWriter :: forall w effs a. Monoid w => Eff (Writer w ': effs) a -> Eff effs (a, w)

Simple handler for Writer effects.