#10011: The Data instance for Ratio violates internal invariants. -------------------------------------+------------------------------------- Reporter: ekmett | Owner: ekmett Type: bug | Status: new Priority: normal | Milestone: Component: Core | Version: 7.10.1-rc1 Libraries | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I found this when Simon was cleaning up unused dependencies in {{{ https://phabricator.haskell.org/rGHCc409b6f30373535b6eed92e55d4695688d32be9e... }}} The Data instance for Ratio just uses the raw `(:%)` constructor and doesn't check that the result is reduced to normal form. It strikes me that the fix is to add back the Integral constraint on the Data instance and to use `(%)` rather than `(:%)` in the `gfoldl` and `gunfold` code. This restores the invariant and matches the behavior of "virtual constructors" we've used to patch up such problems elsewhere. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10011 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler