[Haskell-cafe] Ambiguous occurence error, despite use of DuplicateRecordFields (worked with ghc 8.10.7, not with 9.6.4)
Tom Ellis
tom-lists-haskell-cafe-2023 at jaguarpaw.co.uk
Tue Apr 9 12:17:47 UTC 2024
I see, thanks. So it does look like my wild guess was correct. GHC
will no longer disambiguate ambiguous field selectors. Perhaps you're
supposed to use OverloadedRecordDot for this (I'm not sure, I don't
use it myself).
Tom
On Tue, Apr 09, 2024 at 01:57:48PM +0200, Han Joosten wrote:
> 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
>
> Op di 9 apr 2024 om 12:38 schreef Tom Ellis <
> tom-lists-haskell-cafe-2023 at jaguarpaw.co.uk>:
> > 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
> >
> > 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
> >
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