Re: Ambiguous occurence error, despite use of DuplicateRecordFields (worked with ghc 8.10.7, not with 9.6.4)

Hi Tom,

The code can be found here:
https://github.com/AmpersandTarski/Ampersand/blob/upgrade-ghc/src/Ampersand/Core/ParseTree.hs

The idea is that I have several data definitions each with a field named
`pos`. I have a class that conveniently gets that field from whatever
instance. This used to work, but now is broken:

data Foo = Foo
   { pos :: !Origin,
     ... other fields
   }
data Bar = Bar
    { pos :: !Origin,
     ... other fields
   }

class Traced a where
   origin :: a -> Origin

instance Traced Foo where
  origin = pos

instance Traced  Bar  where
  origin = pos

Of course I could rewrite the instance definitions something like

instance Traced Foo where
  origin (Foo{pos = p} = p

but that looks ugly, and it feels strange.

Thanks for replying



Op di 9 apr 2024 om 12:38 schreef Tom Ellis <
[email protected]>:

> Hello Han,
>
> Would it be possible to produce a minimal example that demonstrates
> the problem?  Or at the very least share the code?  It's very hard to
> know where to start diagnosing.  (Although perhaps someone else knows
> without having to see code.)
>
> At a wild guess, have you been hit by this?
>
> > As of GHC 9.4.1, selector names have to be entirely unambiguous
> > (under the usual name resolution rules), while for record updates,
> > there must be at most one datatype that has all the field names
> > being updated.
>
>
> https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/duplicate_record_fields.html#extension-DuplicateRecordFields
>
> Tom
>
>
>
> On Tue, Apr 09, 2024 at 12:18:14PM +0200, Han Joosten wrote:
> > Hi all,
> >
> > I am currently migrating a Haskell project that uses ghc 8.10.7 to ghc
> > 9.6.4.
> >
> > Using the new version, I get errors like
> >
> > ~~~.haskell
> > Ambiguous occurrence ‘pos’
> > It could refer to
> >    either the field ‘pos’ of record ‘PClassify’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1265:5
> >        or the field ‘pos’ of record ‘PPurpose’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1186:5
> >        or the field ‘pos’ of record ‘P_ViewSegment’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1129:5
> >        or the field ‘pos’ of record ‘P_ViewD’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1080:5
> >        or the field ‘pos’ of record ‘P_IdentDf’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:1024:5
> >        or the field ‘pos’ of record ‘P_BoxItem’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:981:9
> >        or the field ‘pos’ of record ‘TemplateKeyValue’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:959:5
> >        or the field ‘pos’ of record ‘BoxHeader’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:947:5
> >        or the field ‘pos’ of record ‘P_SubIfc’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:934:9
> >        or the field ‘pos’ of record ‘P_Interface’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:899:5
> >        or the field ‘pos’ of record ‘P_Population’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:870:9
> >        or the field ‘pos’ of record ‘P_Rule’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:806:5
> >        or the field ‘pos’ of record ‘PairViewSegment’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:740:9
> >        or the field ‘pos’ of record ‘P_NamedRel’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:591:5
> >        or the field ‘pos’ of record ‘PAtomPair’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:467:5
> >        or the field ‘pos’ of record ‘Pragma’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:415:5
> >        or the field ‘pos’ of record ‘P_Relation’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:408:5
> >        or the field ‘pos’ of record ‘Representation’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:339:5
> >        or the field ‘pos’ of record ‘PConceptDef’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:268:5
> >        or the field ‘pos’ of record ‘P_Pattern’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:209:5
> >        or the field ‘pos’ of record ‘Role’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:185:5
> >        or the field ‘pos’ of record ‘P_RoleRule’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:172:5
> >        or the field ‘pos’ of record ‘P_Enforce’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:152:5
> >        or the field ‘pos’ of record ‘MetaData’,
> >           defined at
> > /workspaces/AmpersandNamespace/src/Ampersand/Core/ParseTree.hs:136:5
> >
> > Previously, it was totally fine to have different data types each have a
> > field with the same name, as long as you used `DuplicateRecordFields`
> >
> > I have searched the migration documentation but I couldn't find any clue
> on
> > why this has been changed or how to deal with it. I probably missed it.
> > Any help is mostly appreciated!
> >
> > Thanks for reading
> > Cheers,
> > Han Joosten
>
> > _______________________________________________
> > Haskell-Cafe mailing list
> > To (un)subscribe, modify options or view archives go to:
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> > Only members subscribed via the mailman list are allowed to post.
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

_______________________________________________
Haskell-Cafe mailing list
To (un)subscribe, modify options or view archives go to:
http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
Only members subscribed via the mailman list are allowed to post.