safe vs. unsafe (Was: Haskell Platform proposal: Add the vector package)

John Lato jwlato at
Mon Jul 16 02:15:38 CEST 2012

> On Sat, Jul 14, 2012 at 3:16 AM, Henning Thielemann <
> lemming at> wrote:
>> On Fri, 13 Jul 2012, Brandon Allbery wrote:
>>  And now I'm having a "so what's the point?" moment?  All this effort so
>>> we can just mark random stuff as
>>> Trusted anyway?
>> Today we have 'unsafePerformIO'. So if we praise the merits of Haskell's
>> strong type system and then mention 'unsafePerformIO' the audience will ask
>> "so what's the point of type safety then?" Well, the point is that
>> unsafePerformIO is strongly discouraged and every use of it should be
>> considered carefully.
> We've just been told *not* to consider carefully for purposes of marking a
> module as Trustworthy; an argument based on considering carefully is not
> relevant.

I think the idea here is that, as a package author, it's okay to just
throw Trustworthy anywhere ghc can't infer Safe on its own.  As a
package user, if you care about Safe Haskell, it's your responsibility
to audit/consider carefully to determine if Trustworthy code is
something you're willing to include in your codebase.

John L.

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