Re: deprecating

On 23/10/12 02:36, Simon Marlow wrote:
>> I think it means "I require at least rank-2 types".
>>
>> To clarify, I think it's OK if a compiler accepts a program marked
>> "Rank2Types" and incorrectly not marked "RankNTypes" when it actually
>> requires rank-n types.
>
> I don't think I understand why you would want an extension flag to 
> mean "at least" rather than "at most".  No other extension flag works 
> that way.  If you take that view to its logical conclusion, we would 
> never need to specify any extension flags at all.
>
> Rank2Types is only useful if it really means rank-2 types, which it 
> apparently doesn't, so I'm quite happy to deprecate it.  We don't have 
> to actually remove it for a long time, since the cost of maintaining 
> one flag that is a synonym for another flag is small.

Sorry, you're right. It means "I require at most rank-2 types"

Program A is marked "Rank2Types" and not "RankNTypes" and uses only 
rank-1 types.
Program B is marked "Rank2Types" and not "RankNTypes" and uses only 
rank-1 & rank-2 types.
Program C is marked "Rank2Types" and not "RankNTypes" and uses rank-3 types.

The compiler MUST accept A & B. It SHOULD reject C, but since GHC can't 
tell the difference, it's acceptable if it accepts it.

-- Ashley