#10570: Too restrictive liberate coverage condition -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Description changed by danilo2: Old description:

Hello! Let's look at this small example:

{{{haskell class ConsByIdx2 x a m cls | x -> m where consByIdx2 :: x -> a -> m cls

instance ConsByIdx2 Int a Proxy cls where consByIdx2 _ _ = Proxy }}}

It fails to compile with the following error:

{{{haskell Illegal instance declaration for ‘ConsByIdx2 Int a Proxy cls’ The liberal coverage condition fails in class ‘ConsByIdx2’ for functional dependency: ‘x -> m’ Reason: lhs type ‘Int’ does not determine rhs type ‘Proxy’ In the instance declaration for ‘ConsByIdx2 Int a Proxy cls’ }}}

But Int determines the Proxy in a nice way.

New description: Hello! Let's look at this small example: {{{ class ConsByIdx2 x a m cls | x -> m where consByIdx2 :: x -> a -> m cls instance ConsByIdx2 Int a Proxy cls where consByIdx2 _ _ = Proxy }}} It fails to compile with the following error: {{{ Illegal instance declaration for ‘ConsByIdx2 Int a Proxy cls’ The liberal coverage condition fails in class ‘ConsByIdx2’ for functional dependency: ‘x -> m’ Reason: lhs type ‘Int’ does not determine rhs type ‘Proxy’ In the instance declaration for ‘ConsByIdx2 Int a Proxy cls’ }}} But Int determines the Proxy in a nice way. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10570#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10570: Too restrictive liberate coverage condition -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by danilo2): * status: new => closed * resolution: => invalid -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10570#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10570: Terrible error message with fundeps and PolyKinds -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"2d06a9f19d5b3ab8c3ff0b24f508c15bedae99d2/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="2d06a9f19d5b3ab8c3ff0b24f508c15bedae99d2" Improve error message for fundeps Improve error message fundeps, especially when PolyKinds means that the un-determined variables are (invisible) kind variables. See Trac #10570. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10570#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10570: Terrible error message with fundeps and PolyKinds -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.1 Resolution: fixed | Keywords: FunDeps Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => FunDeps -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10570#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler