#15627: Absent unlifted bindings -------------------------------------+------------------------------------- Reporter: sgraf | Owner: (none) Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 8.4.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #9279 #4328 | Differential Rev(s): #11126 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgraf): We need the `Eq` instance of `Literal` when deriving `Eq AltCon`. That's OK, we have `eqType` for that. However, there's also an instance `Ord AltCon` that is a little shady (sic): {{{ -- This instance is a bit shady. It can only be used to compare AltCons for -- a single type constructor. Fortunately, it seems quite unlikely that we'll -- ever need to compare AltCons for different type constructors. -- The instance adheres to the order described in [CoreSyn case invariants] instance Ord AltCon where compare (DataAlt con1) (DataAlt con2) = ASSERT( dataConTyCon con1 == dataConTyCon con2 ) compare (dataConTag con1) (dataConTag con2) compare (DataAlt _) _ = GT compare _ (DataAlt _) = LT compare (LitAlt l1) (LitAlt l2) = compare l1 l2 compare (LitAlt _) DEFAULT = GT compare DEFAULT DEFAULT = EQ compare DEFAULT _ = LT }}} I will not try and remove that instance, I think it's probably needed somewhere. Questions: 1. How would I implement `cmpType`, which I'd need for a faithful `cmpLit` function? 2. In the likely case the answer to 1) is "don't", then does sound ignoring the `MachNull` type in comparisons OK? E.g. `cmpType (MachNull _) (MachNull_) = EQ`. Makes `Ord AltCon` a little more shady than it already is, but still seems in line with the invariant "only use on AltCons of same type constructor". Also, `cmpType` and `eqType` might then disagree. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15627#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler