#16140: Cannot create type synonym for quantified constraint without ImpredicativeTypes -------------------------------------+------------------------------------- Reporter: Ashley Yakeley | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): This is an interesting question. When written to the left of an `=>`, the parentheses delimit a list that is inlined. However, in a type synonym, you're really building a tuple. So GHC's behavior here is just a manifestation of this internal design... but the design shouldn't leak this way. I would classify it as a bug, yes. It's unclear to me how to solve it, though, especially because GHC struggles to tell constraint tuples apart from normal ones. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16140#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler