#4485: Unexplained change in type-inference + OverlappingInstances in ---------------------------------+------------------------------------------ Reporter: JeremyShaw | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.0.1 RC1 Keywords: | Testcase: Blockedby: | Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: GHC rejects valid program ---------------------------------+------------------------------------------ Changes (by nibro):
* cc: niklas.brob...@… (added) Comment: The intended intuition is that whenever we come upon an unconstrained use of `genElement`, which produces some `XMLGenT m1 (XML m1)` where we can't resolve `m1`, but where we are within the context of some `XMLGen m` that we're embedding it in, default to `m1` = `m`. In other words, I would expect that the third alternative above defaulted to whenever we cannot actually infer that `m1` = `Identity`. Reading up on the documentation again, maybe this is exactly what IncoherentInstances does after all? What worries me is that IncoherentInstances might cause the third alternative to be chosen "too early", but maybe that's just superstition. -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4485#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler _______________________________________________ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs