Use MTL: Accum, State, SelectT, ContT

[kamil-adam]

• Use AccumT for (w -> m (a, w)) parser:
  • https://hackage.haskell.org/package/mtl-2.3.1/docs/Control-Monad-Accum.html
• Use StateT for (s -> m (a, s)) parser:
  • https://hackage.haskell.org/package/mtl-2.3.1/docs/Control-Monad-State-Strict.html#t:State
• Use SelectT for ((a -> m r) -> m a) selecting:
  • https://hackage.haskell.org/package/transformers-0.5.6.2/docs/Control-Monad-Trans-Select.html#t:SelectT
• Use ContT for (a -> m r) -> m r continuation:
  • https://hackage.haskell.org/package/transformers-0.5.6.2/docs/Control-Monad-Trans-Cont.html#t:ContT

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• Change name Unit to Automaton