Sequence.hs

{-# LANGUAGE TupleSections #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module Control.Monad.Schedule.Sequence where

-- base
import Control.Arrow ((>>>))
import Control.Monad.IO.Class
import qualified Data.List.NonEmpty as NonEmpty

-- transformers
import Control.Monad.Trans.Class

-- monad-schedule
import Control.Monad.Schedule.Class

-- | Any monad can be trivially scheduled by executing all actions sequentially.
newtype SequenceT m a = SequenceT { unSequence :: m a }
  deriving (Functor, Applicative, Monad, MonadIO)

instance MonadTrans SequenceT where
  lift = SequenceT

-- | Execute all actions in sequence and return their result when all of them are done.
--   Essentially, this is 'sequenceA'.
instance Monad m => MonadSchedule (SequenceT m) where
  schedule = sequenceA >>> fmap (, [])