A monad transformer that allows recording the results of monadic actions and allows replaying them later so that the application can resume from the same point.
Results of a RecorderT computation are recorded in a running journal
using the record combinator. A computation can be paused at any point
using the pause primitive returning a Recording that can be used to
restart the computation from the same point later. When the recording is
replayed, the record combinator returns the previously recorded result of
the computation from the journal being replayed instead of actually running the
computation again.
import Control.Monad.IO.Class (liftIO)
import Control.Monad.Trans.Recorder (runRecorderT, record, pause, Paused(..), blank)
import Control.Exception (catch)
main = do
recording <- (runRecorderT blank computation >> return blank)
`catch` \(Paused r) -> return r
putStrLn "Computation paused, resuming again with recorded logs"
runRecorderT recording computation
return ()
where
computation = do
x1 <- record $ liftIO $ return 1
record $ liftIO $ print ("A", x1)
x2 <- record $ liftIO $ return 2
record pause
record $ liftIO $ print ("B", x1, x2)This package is inspired by the logging implementation in the transient
package by Alberto G. Corona. Related packages: