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

On Wed, 9 Jan 2008, David Roundy wrote:

On Jan 9, 2008 4:21 PM, Don Stewart wrote:

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anton:

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OTOH, the freedom to change things on the fly can be nice to have, and if used with "great responsibility" (mainly an understanding of what's safe to do and what isn't), the downside can be vanishingly small.

It can be small, unless you need to have any kind of static assurance (say for high assurance software, or for new kinds of optimisations, or if you want to reorder code in the compiler for parallelism).

Then the downside to arbitrary, untracked effects in the system is huge.

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.

Indeed, there are hacks and they are some times necessary. The good thing about Haskell is, that hacks look like hacks. 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? Wouldn't this also simplify http://www.haskell.org/haskellwiki/Safely_running_untrusted_Haskell_code ?