The fact that using `dataToTag#` directly produces incorrect results is
#15696: Derived Ord instance for enumerations with more than 8 elements seems to be incorrect -------------------------------------+------------------------------------- Reporter: mrkkrp | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.6.2 Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:16 RyanGlScott]: perhaps not terribly surprising... Except that we have special code to make sure that always happens regardless. The STG Simon pasted looks right from that standpoint: it always applies `dataToTag#` under a case on its argument. So my bet is that Simon is right: something is going wrong in code generation or the RTS. Side note: it looks like I was wrong about tagging large types. I believe there was some talk of that, but it doesn't look like it's happened as yet. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15696#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler