#7066: isInstance does not work for compound types -------------------------------------+------------------------------------ Reporter: edsko | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Template Haskell | Version: 7.4.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by mojojojo): I just got hit by this issue. I would expect {{{ isInstance clss typs }}} to return True if and only if I can safely generate code (in my Template Haskell code) that relies on 'typs' being an instance of 'clss'. In the example above, I can not safely generate code that relies on a Show instance for (Int, A) because there is no Show instance for A. I expected exactly the same. That's why I believe that the current behaviour of the function is unintuitive to say the least. The documentation has no info concerning such behaviour either. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7066#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler