Re: [Haskell-cafe] Why purely in haskell?

On Thu, 10 Jan 2008, David Roundy wrote:

On Thu, Jan 10, 2008 at 08:10:57PM +0000, Sebastian Sylvan wrote:

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On Jan 10, 2008 8:06 PM, Ketil Malde wrote:

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"David Roundy" writes:

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I just want to point out that unsafePerformIO is at the core of the (safe) bytestring library. As SPJ et al pointed out, this is crucial functionality, and is only unsafe if unsafely used.

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In Modula-3 modules using hacks must be explicitly marked as UNSAFE. See http://www.cs.purdue.edu/homes/hosking/m3/reference/unsafe.html Maybe this is also an option for Haskell?

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I don't think this is a good idea.

I think the point is (should be) to mark functions unsafe when they may be unsafe to /use/,

I think using the IO monad for this works well...

Would you suggest moving head and tail into the IO monad?

I'm afraid we are talking about different notions of 'safe'. Modula-3's 'safe' means no "segmentation fault", but program abortion due to ASSERT is still allowed. Ported to Haskell this means: 'head' and 'tail' are safe, but not total. I've seen function definitions like 'safeHead', that I would have named 'maybeHead'. For running untrusted code this means: I think it is ok that the program aborts with an error or runs into an infinite loop and must be terminated after a time-out, but it is not ok, that it overwrites some memory area or deletes some files, because unsafePerformIO was invoked.