#14331: Overzealous free-floating kind check causes deriving clause to be rejected -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler (Type | Version: 8.2.1 checker) | Resolution: | Keywords: deriving Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | deriving/should_compile/T14331 Blocked By: | Blocking: 15376 Related Tickets: #15376 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Visible kind application adds another layer of screwball-ery to the mix: {{{#!hs {-# LANGUAGE GeneralizedNewtypeDeriving #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeApplications #-} module Bug where import Data.Kind class Cat (cat :: k -> k -> Type) instance Cat (->) newtype Fun1 a b = Fun1 (a -> b) deriving (Cat @k) }}} {{{ $ ~/Software/ghc/inplace/bin/ghc-stage2 --interactive Bug.hs -ddump-deriv -fprint-explicit-kinds GHCi, version 8.7.20190105: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) ==================== Derived instances ==================== Derived class instances: instance Bug.Cat @* Bug.Fun1 where Derived type family instances: Ok, one module loaded. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14331#comment:68 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler