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

[Andrew Coppin]

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.