Re: [GHC] #12468: GADTs don't refine hole types

#12468: GADTs don't refine hole types -------------------------------------+------------------------------------- Reporter: benjamin.hodgson | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #11325 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"433b80dec1cfef787fc1327a9eada1791b11c12e/ghc" 433b80d/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="433b80dec1cfef787fc1327a9eada1791b11c12e" Ensure that insolubles are fully rewritten I was alerted to this by Trac #12468 and #11325. We were treating insolubles (and "hole" constraints are treated as insoluble) inconsistently. In some places we were carefully rewriting them e.g. Note [Make sure that insolubles are fully rewritten] in TcCanonical. But in TcSimplify we weren't feeding them into the solver. As a result, "hole" constraints were not being rewritten, which some users found confusing, and I think rightly so. This patch also fixes a bug in TcSMonad.emitInsoluble, in which two different "hole" constriants could be treated (bogusly) as duplicates, thereby losing one. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12468#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler