#9526: Add missing Generic instances in base -------------------------------------+------------------------------------- Reporter: nh2 | Owner: dreixel Type: feature request | Status: closed Priority: normal | Milestone: Component: Core Libraries | Version: 7.8.3 Resolution: wontfix | Keywords: Generics Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #10512 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * related: => #10512 Comment: Sorry, my bad. I linked the wrong issue. It should be #10512, where `Generic` instances were proposed for `Int32` and `Word64`. The resolution of that issue is wontfix, and in GHC 8.0, the `Generic` instances for `Char`, `Float`, `Double`, and `Int` [https://ghc.haskell.org/trac/ghc/ticket/10512#comment:7 will be removed]. Pedro outlines the reasons for not including `Generic` instances for primitive types [https://ghc.haskell.org/trac/ghc/ticket/10512#comment:3 here]. Basically, `Generic` instances are intended for inspecting the structure of regular, structured algebraic data types until you get down to the "leaves" of a data structure. The leaves only require //ad hoc// instances of the base class, not of `Generic`. Moreover, the previous `Generic` instances base types were lying to users. Previously, we had something like this: {{{#!hs type Rep Char = D1 D_Char (C1 C_Char (S1 NoSelector (Rec0 Char)) }}} But according to the rules of how `Generic` operates, that would suggest that `data Char = Char Char`, which is absolutely not the case. To avoid this dishonesty, we decided to remove the offending instances altogether. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9526#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler