#10011: The Data instance for Ratio violates internal invariants. -------------------------------------+------------------------------------- Reporter: ekmett | Owner: ekmett Type: bug | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 7.10.1-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Description changed by ekmett: Old description:
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.
New description: 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#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler