#13795: :kind! is not expanding type synonyms anymore --------------------------------------+--------------------------------- Reporter: Hjulle | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Linux Architecture: x86_64 (amd64) | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+--------------------------------- Given {{{#!hs type A = () :kind! A }}} Expected result: {{{#!hs A :: * = () }}} Actual result: {{{#!hs A :: * = A }}} ---- Some IRC conversation on the topic (on #ghc): {{{ 23:37 < hjulle> :kind! does not seem to expand type synonyms for me (in GHC 8.0.2), it just prints them verbatim. Does anyone else have this problem? Example: "type A = ()" ":kind! A" will print out "A :: * = A" (which is not very helpful). 23:40 < hjulle> Is this a bug? The documentation (https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ghci.html #ghci-cmd-:kind) explicitly states that :kind! should expand type synonyms, so I think yes? 23:57 < RyanGlScott> hjulle: That's absolute a bug. File a ticket! 23:57 < RyanGlScott> *absolutely 23:58 < RyanGlScott> Moreover, I know why that's happening 23:59 < RyanGlScott> Internally, :kind! uses the normalise_type function to reduce type families: http://git.haskell.org/ghc.git/blob/e77b9a2069bca9018f989d7c4f54da099e3ab215... 23:59 < RyanGlScott> But see the comment there Day changed to 07 jun 2017 00:00 < RyanGlScott> -- Try to not to disturb type synonyms if possible 00:01 < RyanGlScott> So fixing this would just be a matter of calling coreView afterwards (which expands type synonyms) 00:02 < RyanGlScott> er, actually, expandTypeSynonyms is even better: http://git.haskell.org/ghc.git/blob/e77b9a2069bca9018f989d7c4f54da099e3ab215... }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13795 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler