#13962: GHCi allows unsaturated type family -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: wontfix | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #12089, #16013 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * related: #12089 => #12089, #16013 Comment: Note that we opted to disallow unsaturated type synonyms/families in GHCi when not at the top level in commit [https://gitlab.haskell.org/ghc/ghc/commit/6b70cf611e5ddc475edaa54b893d209906... 6b70cf611e5ddc475edaa54b893d20990699ddb8]: {{{ commit 6b70cf611e5ddc475edaa54b893d20990699ddb8 Author: Ryan Scott <ryan.gl.scott@gmail.com> Date: Tue Jan 8 07:37:18 2019 -0500 Be pickier about unsaturated synonyms in :kind Summary: We currently permit any and all uses of unsaturated type synonyms and type families in GHCi's `:kind` command, which allows strange interactions like this one: ``` > :set -XTypeFamilies -XPolyKinds > type family Id (a :: k) > type instance Id a = a > type Foo x = Maybe > :kind! Id Foo ``` This is probably a stretch too far, so this patch moves to disallow unsaturated synonyms that aren't at the top level (we still want to allow `:kind Id`, for instance). We do this by augmenting `GhciCtxt` with an additional `Bool` field to indicate if we are at the outermost level of the type being passed to `:kind` or not. See `Note [Unsaturated type synonyms in GHCi]` in `TcValidity` for the full story. Test Plan: make test TEST=T16013 Reviewers: goldfire, bgamari Reviewed By: goldfire Subscribers: simonpj, goldfire, rwbarton, carter GHC Trac Issues: #16013 Differential Revision: https://phabricator.haskell.org/D5471 }}} See #16013. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13962#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler