[Haskell-cafe] Just for a laugh...

Andrew Coppin andrewcoppin at btinternet.com
Fri Jun 1 14:39:32 EDT 2007

David Roundy wrote:
> On Fri, Jun 01, 2007 at 07:28:07PM +0100, Andrew Coppin wrote:
>> David Roundy wrote:
>>> Note also that you can use unsafePerformIO to safely get pure functions
>>> doing both these operations.
>> I've always been puzzled by this one... how does unsafePerformIO 
>> circumvent the type system? I don't understand.
> It's a primitive.  You couldn't implement it unless you're the
> compiler-writer.  But it's a necesary primitive, if you wish to build
> efficient data types.  You just need to carefully audit everywhere that
> unsafePerformIO is used.

No, I mean... how could you use unsafePerformIO to perform a typecast? I 
don't see a way to do that.

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