If I replace it with
mkHsForAllTy :: HsExplicitFlag -> [LHsTyVarBndr RdrName] -> LHsContext
RdrName -> LHsType RdrName -> HsType RdrName
-- Smart constructor for HsForAllTy
-- mkHsForAllTy exp tvs (L _ []) ty = mk_forall_ty exp tvs ty
mkHsForAllTy exp tvs (L _ []) ty = HsForAllTy exp Nothing (mkHsQTvs tvs) (L
noSrcSpan []) ty
mkHsForAllTy exp tvs ctxt ty = HsForAllTy exp extra (mkHsQTvs tvs)
cleanCtxt ty
where -- Separate the extra-constraints wildcard when present
(cleanCtxt, extra)
| (L l HsWildcardTy) <- ignoreParens (last (unLoc ctxt)) = (init
`fmap` ctxt, Just l)
| otherwise = (ctxt, Nothing)
ignoreParens (L _ (HsParTy ty)) = ty -- TODO:AZ We lose the
annotation here
ignoreParens ty = ty
I get the following errors in the stage 2 compile (only first 3 shown here)
libraries/ghc-prim/GHC/Classes.hs:52:19:
Malformed instance: (Eq a, Eq b) => Eq (a, b)
libraries/ghc-prim/GHC/Classes.hs:53:19:
Malformed instance: (Eq a, Eq b, Eq c) => Eq (a, b, c)
libraries/ghc-prim/GHC/Classes.hs:54:19:
Malformed instance: (Eq a, Eq b, Eq c, Eq d) => Eq (a, b, c, d)
Alan
On Fri, Apr 10, 2015 at 12:14 AM, Simon Peyton Jones
Hmm. I’m not sure what the motivation is either. Try dropping it out and see if anything goes wrong.
Simon
*From:* ghc-devs [mailto:ghc-devs-bounces@haskell.org] *On Behalf Of *Alan & Kim Zimmerman *Sent:* 09 April 2015 22:15 *To:* ghc-devs@haskell.org *Subject:* Collapsing HsForAllTy, again
With the help of Jan Stolarek I tracked down the HsForAllTy flattening to `HsTypes.mk_forall_ty`.
This function takes any nested HsForAllTy's where the top one does not have a context defined, and collapses them into a single one.
I do not know what the motivation for this is, and if it perhaps speeds up or simplifies further compilation.
But now that API Annotations have arrived, making sure we do not lose the annotations for the sub-HsForAllTy causes significant gymnastics in the parser [1].
So my question is, is there a good reason to continue doing this, given the trade-off in parser complexity.
Regards
Alan