Control.Monad.Freer.Writer

Writer effects, for writing changes to an attached environment.

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

Documentation

data Writer o x where

Writer effects - send outputs to an effect environment

Constructors

Writer :: o -> Writer o ()

tell :: Member (Writer o) r => o -> Eff r ()

Send a change to the attached environment

runWriter :: Eff (Writer o : r) a -> Eff r (a, [o])

Simple handler for Writer effects