> What you suggest would be fine with me. Presumably ExplicitForall would be 
> implied by RankNTypes and the other extensions?

Yes, that's the idea. Rank2Types, RankNTypes, PolymorphicComponents,
ScopedTypeVariables and LiberalTypeSynonyms would all imply
ExplicitForall.

> There is a danger of having too *many* choices. 
> (http://www.joelonsoftware.com/items/2006/11/21.html)  In particular, you 
> might consider making ScopedTypeVariables synonymous with ExplicitForAll.  
> Once you have given up the keyword, it seems a shame not to allow lexically 
> scoped type variables!

While I agree with you (and Joel) in principle, I think this is the
wrong level to hold that discussion. I think the long-term solution
should be to keep the registered extensions cleanly separated, and
instead supply extension *groups* as a way to limit choice.
-fglasgow-exts has fit that niche admirably for a long time, I think a
lot of people just use that without thinking twice about what
particular extensions they actually use, and nothing wrong with that.
I think the move towards LANGUAGE pragmas instead of compiler options
is a good one from a standardisation and implementation point of view,
but to avoid tedium and unnecessary choice for the programmer I
strongly feel that extension groups need to be introduced at this
level too. But as I said, that's for a different discussion...

> On ExistentialQuantification, I personally think we should deprecate the 
> entire construct, suggesting GADT-style syntax instead.

+1, though I was afraid to suggest something that radical. I might
write a separate proposal for that then, to keep the discussion here
focused on ExplicitForall.

> If you can form a consensus, go for it.

Alright, let's set an actual discussion period of 2 weeks for
ExplicitForall. If there is no opposition by then, we can add
ExplicitForall to the registered extensions in cabal as a first step.

Cheers,

/Niklas
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