#15052: DeriveAnyClass instances may skip TypeError constraints -------------------------------------+------------------------------------- Reporter: jcpetruzza | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: | CustomTypeErrors Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by jcpetruzza): Let's forget about the program in comment:1, I understand what GHC is doing there and I agree it is the expected behaviour. :) The issue is only shown in the program of comment:5. In this program ** `C` has an empty context**, so writing {{{#!haskell data TS = TSL | TSR deriving (Gen.Generic, C) }}} and writing {{{#!haskell data TS = TSL | TSR deriving (Gen.Generic) instance C TS }}} should have the same result, but it doesn't. The first form is accepted, the second one is rejected (as expected). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15052#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler