Re: a reliable way of dropping levity args?

I finally had some time to have another look. I have this line in my compiler pass: | 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) This is one of the outputs: elimUbxSumRepTypes orig args: ['Lifted, 'Lifted, 'Lifted, String, String, String] dropWhile isLevityTy args = ['Lifted, 'Lifted, 'Lifted, String, String, String] Am I doing this wrong? 2016-01-25 7:30 GMT-05:00 Richard Eisenberg :

As discussed on IRC, your approach below looks right to me: dropWhile (isLevityTy . idType) args. But you then said this wasn't working for you. What does (map idType args) say?

Richard

On Jan 24, 2016, at 8:58 PM, Ömer Sinan Ağacan wrote:

...

Hi all,

I'm looking for a reliable way of dropping levity args from TyCon applications. When I know that a particular TyCon gets some number of levity args, I can just drop the args manually (for example, I can drop the first half of arguments of a tuple TyCon application) but the code looks fragile (what happens if I use a different TyCon in the future) and confusing to the reader because it looks like this:

drop (length args `div` 2) args

Ideally it'd look like this:

dropWhile isLevityArg args

Now, there's a function called isLevityTy, but I don't understand what it's supposed to do. This doesn't do anyting to 'Boxed and 'Unboxed arguments:

dropWhile (isLevityArg . idType) args

Any ideas on this?

Thanks..