#14292: Coercing between constraints of newtypes -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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 goldfire): Ryan is, as usual, spot on. The need for `-XIncoherentInstances` in Ryan's example was a deliberate design choice to discourage non-nominally roled classes. And the extension name is accurate: you're using instances in a fundamentally incoherent (but still type-safe) way. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14292#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler