Re: Bug: GHC hangs rather than reporting an occurs check error

On Thu, Mar 20, 2008 at 02:38:56AM -0400, Bryan Donlan wrote:

I've found a case where GHC will hang (consuming more and more memory) when it should report an occurs check error. The test case is at http://fushizen.net/~bd/kaos-ghc.loop.tgz - the error in question is that the arguments in the StateT instance for HOLift are reversed like so:

-instance HOLift m (StateT s m) where +instance HOLift (StateT s m) m where

I haven't looked at this in detail, but you have enabled the UndecidableInstances extension, so it's not necessarily a bug if the type checker goes into a loop. Thanks Ian