#2456: For higher kinds, instance declarations need quantification in the context -------------------------------+-------------------------------------------- Reporter: ronwalf | Owner: Type: feature request | Status: new Priority: normal | Milestone: _|_ Component: Compiler | Version: 6.9 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: x86 Failure: None/Unknown | Difficulty: Unknown Testcase: | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- Changes (by morabbin): * failure: => None/Unknown * os: MacOS X => Unknown/Multiple Comment: Once one adds {{{ {-# LANGUAGE OverlappingInstances, TypeOperators, StandaloneDeriving, MultiParamTypeClasses, FlexibleInstances, DeriveDataTypeable #-} }}} 7.6.1 yields: {{{ 1 of 1] Compiling DerivingError ( DerivingError.hs, interpreted ) DerivingError.hs:81:1: Duplicate type signature: DerivingError.hs:81:1-33: $tExpr :: Data.Data.DataType DerivingError.hs:80:1-35: $tExpr :: Data.Data.DataType DerivingError.hs:81:1: Duplicate type signature: DerivingError.hs:81:1-33: $cIn :: Data.Data.Constr DerivingError.hs:80:1-35: $cIn :: Data.Data.Constr }}} Is this the expected behavior? Type system question: do we know that all of these extensions play nicely in a type-theoretic sense? Is the argument that, since they're all expressible in System F_C, we're okay? -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/2456#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler