Refactor cellStep using StateT and lenses?

[turion]

Recently (#57) it has come up again that in essence, the Cell constructor could also be declared as:

data Cell m a b = forall s . Data s => Cell
  { cellState :: s
  , cellStep :: a -> StateT s m b
  }

Is this a good idea?

Advantages

• Potential conceptual clarification
• Code reuse from transformers
  • This might resolve some strictness issues
  • Simplifies and clarifies a lot of implementations where state is manually threaded right now

Disadvantages

• One more level of indirection
• Tying to a specific transformer and library

Work to do

• Use lenses (https://hackage.haskell.org/package/lens-5.0.1/docs/Control-Lens-Zoom.html#v:zoom) to implement the different cell manipulation functions
• Check whether the article still works with such changes