#14609: Per-instance UndecidableInstances -------------------------------------+------------------------------------- Reporter: ryanreich | Owner: (none) Type: feature request | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by AntC): Replying to [ticket:14609 ryanreich]:
Can (or why can't) this also be done for UndecidableInstances?
It can and should; and there's almost certainly a proposal somewhere; or a comment on a ticket on (say) overlaps or FunDeps. See also this [https://people.cs.kuleuven.be/~tom.schrijvers/portfolio/haskell2017a.html recent paper] It's a symptom of Functional Dependencies not getting much love recently/perhaps getting phased out in favour of Type Families. And a great deal of nervousness that GHC's implementation of UndecidableInstances is [https://ghc.haskell.org/trac/ghc/ticket/10675#comment:15 bogus] -- which to me argues we should encourage a per-instance pragma, to limit the bogusness. Perhaps we should try to root out the bogusness: [https://github.com/ghc- proposals/ghc-proposals/pull/56 properly] -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14609#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler