Collapsing HsForAllTy, again
Alan & Kim Zimmerman
alan.zimm at gmail.com
Fri Apr 10 07:01:52 UTC 2015
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)
where -- Separate the extra-constraints wildcard when present
| (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
ignoreParens ty = ty
I get the following errors in the stage 2 compile (only first 3 shown here)
Malformed instance: (Eq a, Eq b) => Eq (a, b)
Malformed instance: (Eq a, Eq b, Eq c) => Eq (a, b, c)
Malformed instance: (Eq a, Eq b, Eq c, Eq d) => Eq (a, b, c, d)
On Fri, Apr 10, 2015 at 12:14 AM, Simon Peyton Jones <simonpj at microsoft.com>
> Hmm. I’m not sure what the motivation is either. Try dropping it out
> and see if anything goes wrong.
> *From:* ghc-devs [mailto:ghc-devs-bounces at haskell.org] *On Behalf Of *Alan
> & Kim Zimmerman
> *Sent:* 09 April 2015 22:15
> *To:* ghc-devs at haskell.org
> *Subject:* Collapsing HsForAllTy, again
> With the help of Jan Stolarek I tracked down the HsForAllTy flattening to
> 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 .
> So my question is, is there a good reason to continue doing this, given
> the trade-off in parser complexity.
>  https://phabricator.haskell.org/D833
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