The reasoning is outlined in the user manual here: http://www.haskell.org/ghc/docs/7.4.1/html/users_guide/safe-haskell.html#saf... Basically, these modules will compile without error if they were to be compiled with -XSafe enabled. Thus, they are safe-inferred. The check does not scrutinize individual functions in any way; all of SH works on the level of module boundaries, as well as packages (whether or not to enforce package trust when compiling clients.) As to why they are safe-inferred, considering they are importing primitive libraries/modules, and the module inlinePerformIO lives in should be marked unsafe, well, I don't know. This is just a simple check, and anything more powerful would likely be considerably more complex and difficult to get right. They should be marked as -XUnsafe since their use in a safe program could cause crashes. It's likely not a conscious choice that this is the case, as much as it is probably an oversight. Many of the core libraries have needed refactoring/changes at the module level due to Safe Haskell (and hence there is now a proliferation of *.Unsafe and *.Safe modules, a la ForeignPtr.) I do not know if the next major version of the ByteString library (0.10) or array has marked these as unsafe or not. They should be if not. Perhaps someone else who's more aware of the new Safe Haskell design can comment further. On Tue, May 8, 2012 at 3:03 PM, Francesco Mazzoli wrote:

Why are http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Data... and http://hackage.haskell.org/packages/archive/array/0.4.0.0/doc/html/Data-Arra... Safe-inferred?

The first one uses inlinePerformIO, so it clearly shouldn't be marked as Safe. Maybe Safe Haskell doesn't check that function? The second is a bit messier since it uses unboxed types and primitive operations... But they clearly should be marked as Unsafe, and it surprises me that Safe Haskell is that relaxed when checking for safe functions.

Francesco.

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