| I'm working on unlifted newtypes. | | In MkId.mkDataConWorkId, I see | | > mkDataConWorkId wkr_name data_con | > | isNewTyCon tycon | > = mkGlobalId (DataConWrapId data_con) wkr_name wkr_ty nt_work_info | > | otherwise | > = mkGlobalId (DataConWorkId data_con) wkr_name wkr_ty alg_wkr_info | | Why is a newtype worker called a wrapper (DataConWrapId)? Note that some | newtype constructors have separate wrappers (which is relatively new). | This doesn't appear to be hurting anything right now, but it's odd, and | there's no commentary on this.
That is indeed odd, I agree. Some points * Newtypes can have wrappers: see Note [Data con wrappers and GADT syntax] in MkId.hs * The "worker" for a newtype data constructor is just a function with a compulsory unfolding, of form (\x. x |> co), where co is the newtype coercion. * I agree that it's not right to describe the "worker" for a newtype data constructor as a "DataConWrapId"; after all, it may have a wrapper too (see previous bullet). * Bu not is it rigt to call it a regular DataConWorkId. Those are *data* constructors, head normal forms, very very special. The kosher thing would be to create a NewtypeWorkId. But that's seems a terrible fiddle, because these things are inlined compulsorily so they never exist for long. Maybe it should just be a vanilla Id. While there are a few places where we do test for data-con-wrap-ids -- eg in isImplicitId -- but remember that these things are inlined so aggressively that we will only see them very briefly. Or leave it as-is, with the above commentary as a Note -- that might be the easiest thing! Might you make a little patch? Simon | -----Original Message----- | From: Richard Eisenberg <r...@cs.brynmawr.edu> | Sent: 25 May 2019 11:50 | To: Simon Peyton Jones <simo...@microsoft.com> | Subject: newtype workers | | Hi Simon, | | I'm working on unlifted newtypes. | | In MkId.mkDataConWorkId, I see | | > mkDataConWorkId wkr_name data_con | > | isNewTyCon tycon | > = mkGlobalId (DataConWrapId data_con) wkr_name wkr_ty nt_work_info | > | otherwise | > = mkGlobalId (DataConWorkId data_con) wkr_name wkr_ty alg_wkr_info | | Why is a newtype worker called a wrapper (DataConWrapId)? Note that some | newtype constructors have separate wrappers (which is relatively new). | This doesn't appear to be hurting anything right now, but it's odd, and | there's no commentary on this. | | Thanks, | Richard _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
