#16246: GHC HEAD-only Core Lint error with unboxed equality (Non-CoVar has coercion type) -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #15648 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): We need the distinction -- if ordinary `Id`s could represent coercions, then nothing is stopping us from having non-terminating coercions, which would kill the type system. (Note that we don't force `CoVar`s when casting by them, as they're computationally irrelevant.) But, there is nothing harmful (or useful, I think) about ordinary `Id`s that have coercion types. As these are not `CoVar`s, they cannot be used in casts (or anywhere else). But I don't see them causing any harm. So, all I'm really worried about is the possibility that someone, somewhere checks whether {{{tyConAppTyCon (idType id) `hasKey` eqPrimTyConKey}}} (or something) instead of checking `isCoVar id`. If we don't ever do that, then an `Id` with a coercion type is just fine. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16246#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler