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