#10100: Bogus "redundant constraint" warning with functional dependencies -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): Humph. In one sense the constraint IS redundant: you simply don't need the evidence (dictionary) for `Add a b ab` to create evidence for `Add (Succ a) b (Succ ab)`. But you want nevertheless to allow this (or not warn about it), because you want to prove things like `Add (Succ Zero) beta (Succ Zero)`, by unifying `beta := Zero`. That won't happen unless you generate the constraint `Add Zero beta Zero`. Hmm, well I suppose we should suppress the warnings where there are functional dependencies. I'll work on it. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10100#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10100: Bogus "redundant constraint" warning with functional dependencies -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: simonpj Type: bug | Status: merge Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | typecheck/should_compile/T10100 | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => merge * testcase: => typecheck/should_compile/T10100 Comment: I've fixed this and added the example as a test. Merge to 7.10 Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10100#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10100: Bogus "redundant constraint" warning with functional dependencies -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: simonpj Type: bug | Status: closed Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_compile/T10100 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"4293a80a3ea835412737911bcb2a6703e9af378b/ghc" 4293a80a/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="4293a80a3ea835412737911bcb2a6703e9af378b" Accommodate API change in transSuperClasses In this patch commit 6eabb6ddb7c53784792ee26b1e0657bde7eee7fb Author: Simon Peyton Jones Date: Tue Dec 15 14:26:13 2015 +0000 Allow recursive (undecidable) superclasses I changed (transSuperClasses p) to return only the superclasses of p, but not p itself. (Previously it always returned p as well.) The use of transSuperClasses in TcErrors.warnRedundantConstraints really needs 'p' in the result -- but I faild to fix this call site, and instead crippled the test for Trac #10100. This patch sets things right * Accomodates the API change * Re-enables T10100 * And thereby fixes Trac #11474 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10100#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler