Trans.hs

{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE RecordWildCards #-}
module LiveCoding.LiveProgram.Monad.Trans where

-- base
import Data.Data

-- transformers
import Control.Monad.Trans.State.Strict

-- essence-of-live-coding
import LiveCoding.LiveProgram
import LiveCoding.Cell.Monad.Trans

-- | Remove a stateful effect from the monad stack by supplying the initial state.
--   This state then becomes part of the internal live program state,
--   and is subject to migration as any other state.
--   Live programs are automatically migrated to and from applications of 'runStateL'.
runStateL
  :: (Data stateT, Monad m)
  => LiveProgram (StateT stateT m)
  ->                     stateT
  -> LiveProgram                m
runStateL LiveProgram { .. } stateT = LiveProgram
  { liveState = State { stateInternal = liveState, .. }
  , liveStep = \State { .. } -> do
      (stateInternal, stateT) <- runStateT (liveStep stateInternal) stateT
      return State { .. }
  }