Re: a reliable way of dropping levity args?

Levity is very simple:

data Levity = Lifted | Unlifted

And that's it, as far as Levity is concerned. The weird thing is TYPE, whose type is Levity -> TYPE 'Lifted. (Yes. TYPE's type mentions TYPE.) The * of yore is now spelled TYPE 'Lifted. The # of yore is now spelled TYPE 'Unlifted. * and # really are just type synonyms. (See them for yourself in GHC.Types.hs.) There is some discussion on wiki:NoSubKinds, but it may be a bit out of date. And, yes, a more obvious function to drop levity arguments (to unboxed tuples, presumably) is a good idea. Richard On Jan 28, 2016, at 8:30 PM, Ömer Sinan Ağacan wrote:

Ahh, levity is type of kinds, right? For some reason I thought kinds are now levities (or whatever it's called). This makes sense. I just tried and I think it works, thanks.

2016-01-28 19:39 GMT-05:00 Richard Eisenberg :

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On Jan 28, 2016, at 5:48 PM, Ömer Sinan Ağacan wrote:

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| Just (tc, args) <- splitTyConApp_maybe ty , isUnboxedTupleTyCon tc = pprTrace "elimUbxSumRepTypes" (text "orig args:" <+> ppr args $$ text "dropWhile isLevityTy args = " <+> ppr (dropWhile isLevityTy args)) $ concatMap go (drop (length args `div` 2) args)

You want (dropWhile (isLevityTy . typeKind) args). isLevityTy simply checks if its argument is exactly `Levity`.

Does that work?

Richard