On 06 October 2004 11:36, Josef Svenningsson wrote:
> Simon Marlow wrote:
>
>> On 06 October 2004 00:53, John Meacham wrote:
>>
>>
>>
>>> This seems like it could be nicely generalized such that all
>>> enumeration types unbox to the unboxed integer of their offset. so
>>>
>>> data Perhaps = Yes | Maybe | No
>>>
>>> can unbox to an Int# with 0# == Yes 1# == Maybe and 2# == No.
>>>
>>>
>>
>> Yes, a strict enumeration should be implemented as an Int#, both in
>> the strictness analyser and also when you {-# UNPACK #-} a
>> constructor field. This is something we'd like to try, but haven't
>> got around to it yet. Maybe a good bite-sized project for a budding
>> GHC hacker? :-)
>>
>>
>>
> Would it really be correct to translate it to Int#? AFAIK, unboxed
> values may not contain bottom while a data type most certainly can. I
> would imagine translating it to Int, and then relying on GHC's
> optimiser to optimize this into Int# whenever possible.
Note I said a *strict* enumeration. You're right that in general it
wouldn't be correct to implement Bool by Int#. Only when the strictness
analyser has determined that a function argument of enumeration type is
strict, or the programmer has added a strictness annotation to a
constructor field.
Certainly right now you can use Int everywhere instead of enumeration
types, and perhaps get better performance because GHC will unbox the Int
whenever possible.
Cheers,
Simon
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