Re: Proposal: GHC.Generics marked UNSAFE for SafeHaskell

Also, I'm not really sure this is a bug, per se. In my opinion when you allow for some sort of generic operations (whether via GHC.Generics or Data), it's roughly equivalent to exporting all the constructors. I don't see how it would work otherwise. But since there's precedent for Typeable, maybe Generics should be restricted in SafeHaskell as well. On Mon, Oct 7, 2013 at 1:05 AM, John Lato wrote:

Well, no. Presumably the example shouldn't compile at all. That message is more an indication that the demonstration is working as intended.

On Mon, Oct 7, 2013 at 12:31 AM, Carter Schonwald < carter.schonwald@gmail.com> wrote:

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i assume https://github.com/JohnLato/safe-bugtest/blob/master/Main.hs#L13should say putStrLn "Should print \"Pos (2)\""

rather than -2?

On Mon, Oct 7, 2013 at 1:23 AM, Carter Schonwald < carter.schonwald@gmail.com> wrote:

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ooo, thats illuminating.

thanks for cooking that up

On Mon, Oct 7, 2013 at 1:13 AM, John Lato wrote:

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On Sun, Oct 6, 2013 at 10:14 PM, Ryan Newton wrote:

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On Sun, Oct 6, 2013 at 6:28 PM, Ganesh Sittampalam wrote:

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- Referential transparency: e.g. no unsafePerformIO

- Module boundary control: no abstraction violation like Template

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Haskell and GeneralizedNewtypeDeriving - Semantic consistency: importing a safe module can't change existing code, so no OverlappingInstances and the like

Is this change necessary to preserve the existing properties, or are

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you hoping to add a new one?

I'm not currently aware of ways to break these invariants *just* with GHC.Generics. Hmm, but I would like to know why it is marked trustworthy and not inferred-safe...

How about this demo repo? https://github.com/JohnLato/safe-bugtest

I'm really not a safe haskell expert, but I believe this is a demonstration of using GHC.Generics to violate a module's abstraction boundaries with SafeHaskell enabled.

If I'm incorrect, I would appreciate if somebody could explain my error. If, however, I'm correct, then I think that Ryan's proposal of marking GHC.Generics Unsafe is the best way to remedy the problem.

A possible stumbling block may involve base and package-trust, but I'm not certain of the current status.

John L.

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