Thanks. I know that "pure" is not thread-safe. I'm quite happy to consider the expressivity of Haskell's monadic approach to effects in a sequential setting first -- much easier to reason about. I wonder if anybody has investigated this expressivity problem. If not, there's an interesting problem waiting to be tackled.
I don't see the problem. Pure code being automatically thread-safe is a boon. I would much rather be unable to write thread-unsafe code without noticing (and able to when I deliberately decide to).
My interest is in proving expressivity results. Such proofs are much easier in a sequential setting. Indeed, at this point I don't even have a strong intuition what exactly the expressivity limitations of Haskell's monadic effect control are.
