I love how this is done in Software Transactional Memory (STM) in Haskell. There, the transaction code happens in its own type (monad), and there is an explicit conversion function called `atomically :: STM a -> IO a`, which carries out the transaction.

This means that the transaction becomes its own block, clearly separated, but which can reference pure values in the surrounding context.

    do
       …
       some IO stuff 
       …
       res <- atomically $ do
          …
          transaction code
          which can reference
          results from the IO above
          …
       …
       More IO code using res, which is the result of the transaction
       …