#14111: strange error when using data families with levity polymorphism and unboxed sums and data families -------------------------------------+------------------------------------- Reporter: carter | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: 13737 | Blocking: Related Tickets: #14457 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): There is precedent with the strategy in comment:21. Note the arity check toward the top of `tcFamTyPats`. This check is fully redundant, but it gives a nice arity error (simple to understand!) instead of an obscure kind error. So, I would say to go with comment:21, with a comment (not sure if it needs a Note) explaining why do the eager check outside of `checkValidDataCon`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14111#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler