#15806: Impredicativity behavior in `:k` command in GHCi -------------------------------------+------------------------------------- Reporter: ningning | Owner: ningning Type: bug | Status: merge Priority: normal | Milestone: 8.6.2 Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #14859 | Differential Rev(s): Phab:D5265 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"c4a876d5f99554e87400946dd26ca11819d11673/ghc" c4a876d5/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="c4a876d5f99554e87400946dd26ca11819d11673" Fix `:k` command: add validity checking Summary: This patch fixes #15806, where we found that the `:k` command in GHCi misses a validity checking for the type. Missing validity checking causes `:k` to accept types that are not validated. For example, `:k (Maybe (forall a. a -> a))` (incorrectly) returns `*`, while impredictivity of type instantiation shouldn't be allowed. Test Plan: ./validate Reviewers: simonpj, goldfire, bgamari Reviewed By: bgamari Subscribers: rwbarton, carter GHC Trac Issues: #15806 Differential Revision: https://phabricator.haskell.org/D5265 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15806#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler