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by dllthomas 3397 days ago
That sounds about right.

At the shallowest level, we can't pass `m ()` to forkIO unless m ~ IO, 'cause the types don't match.

But beyond that, there is the question of how that extra context would be passed through. For something like ReaderT this is straightforward. But consider StateT - `set` in one thread can't be visible in the other.