Separate from whether or not we actually want this -- is it feasible? Here's my situation. When working on parallel programming libraries in Haskell there are very often unsafe operations one wants to do within an otherwise pure model. For example, Accelerate currently violates safe haskell because it trusts the user to provide an associative function to parallel "fold". No associativity, no referential transparency. The solution is to put fold in a separate namespace and mark that module as Unsafe. Likewise for certain monad-par operations that are unsafe. But this factoring can have a serious impact. Not only are extra modules required, but extra type classes as well. For example, if Accelerate is ever refactored for "Safe Haskell" then the following ParAccelerate type class probably should be as well: https://github.com/simonmar/monad-par/blob/5cc656bc45dc473d7a185ec99bb156192... I.e. ParAccelerate & ParAccelerateUnsafe for the "unsafeHybrid" operation. But this starts to be death by a thousand organizational factorings! - The package, abstract-par-accelerate, is already factored out from abstract-par just to avoid an unnecessary Accelerate dependency (which used to mean CUDA errors). (And *another* factoring is possibly warranted for whether or not the module depends on accelerate-io.) - The file would be separate to mark it as Safe Haskell. - The type class ParAccelerateUnsafe would be separate so as to put it in a separate file. What's a possible solution? If, in addition to "Safe" and "Unsafe" modules, there were "Partially Safe" modules, which exported a mix of safe and unsafe identifiers, then this could all be much cleaner. The simple rule is that any reference whatsoever to an unsafe identifier disqualifies the client code. For example, in the above ParAccelerate type class we would mark the unsafeHybrid binding with something like {-# UNSAFE unsafeHybrid #-}. We wouldn't even have to factor it out of the type class. Likewise, Accelerate could mark "fold" as unsafe (providing safe variants as well) without introducing module namespace bloat and confusion. What do you think? -Ryan