[exceptione]

What do you mean with 'cannot'? We have this in [0]

  unsafePerformIO :: IO a -> a 

Do you mean "cannot do with safety guarantee"? Strangely enough, the haskell docs use the same language as you:

  The ST monad allows for destructive updates, but is escapable (unlike IO). 

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0. https://hackage.haskell.org/package/base-4.21.0.0/docs/Syste...