#12102: “Constraints in kinds” illegal family application in instance (+ documentation issues?) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #13780 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): In GHC HEAD (as of commit 2257a86daa72db382eb927df12a718669d5491f8), you get the following error when compiling the original program: {{{ $ inplace/bin/ghc-stage2 --interactive ../Bug.hs GHCi, version 8.7.20181129: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( ../Bug.hs, interpreted ) ../Bug.hs:15:1: error: • Illegal constraint in a kind: forall a. (IsTypeLit a ~ 'True) => a -> * • In the data type declaration for ‘T’ | 15 | data T :: forall a. (IsTypeLit a ~ 'True) => a -> * where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^... }}} Which would suggest that this issue is now moot. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12102#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler