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
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