#16323: Cannot deduce X error with X provided in TypeFamilies ---------------------------------+---------------------------------------- Reporter: pjljvdlaar | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Deriving Operating System: Windows | Architecture: Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | ---------------------------------+---------------------------------------- Comment (by pjljvdlaar): replacing data by newtype give slightly different errors {{{Eq (Ref a)}}} is also required. Adding this to the definition, i.e. {{{#!hs newtype (Referable a, Eq (Ref a), Ord (Ref a), Hashable (Ref a)) => RefMap a = RefMap { -- | the HashMap toHashMap :: HashMap.Map (Ref a) a } deriving (Eq, Ord, Show, Read) }}} still give the same errors for newtype (yet different from data): {{{ C:\TorXakis\sys\txs-basics\src\TorXakis\Test.hs:20:43: error: * Could not deduce (Eq (Ref a)) arising from the 'deriving' clause of a data type declaration from the context: Eq a bound by the deriving clause for `Eq (RefMap a)' at src\TorXakis\Test.hs:20:43-44 Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself * When deriving the instance for (Eq (RefMap a)) | 20 | } deriving (Eq, Ord, Show, Read) | ^^ C:\TorXakis\sys\txs-basics\src\TorXakis\Test.hs:20:47: error: * Could not deduce (Ord (Ref a)) arising from the 'deriving' clause of a data type declaration from the context: Ord a bound by the deriving clause for `Ord (RefMap a)' at src\TorXakis\Test.hs:20:47-49 Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself * When deriving the instance for (Ord (RefMap a)) | 20 | } deriving (Eq, Ord, Show, Read) | ^^^ C:\TorXakis\sys\txs-basics\src\TorXakis\Test.hs:20:52: error: * Could not deduce (Ord (Ref a)) arising from the 'deriving' clause of a data type declaration from the context: (Show a, Referable a) bound by the deriving clause for `Show (RefMap a)' at src\TorXakis\Test.hs:20:52-55 Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself * When deriving the instance for (Show (RefMap a)) | 20 | } deriving (Eq, Ord, Show, Read) | ^^^^ C:\TorXakis\sys\txs-basics\src\TorXakis\Test.hs:20:58: error: * Could not deduce (Ord (Ref a)) arising from the 'deriving' clause of a data type declaration from the context: (Read a, Referable a) bound by the deriving clause for `Read (RefMap a)' at src\TorXakis\Test.hs:20:58-61 Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself * When deriving the instance for (Read (RefMap a)) | 20 | } deriving (Eq, Ord, Show, Read) | ^^^^ -- While building package txs-basics-0.1.0.0 using: C:\sr\setup-exe-cache\x86_64-windows-integersimple\Cabal- simple_Z6RU0evB_2.0.1.0_ghc-8.2.2.exe --builddir=.stack-w ork\dist\67675594 build lib:txs-basics --ghc-options " -ddump-hi -ddump- to-file" Process exited with code: ExitFailure 1 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16323#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler