Actually, I just solved the problem... I think... In my original code, I had the newtype: newtype FilterState t => Filter t a = Filter (ContextMatch t a) deriving (Functor, Monad, MonadReader Email, MonadState Bool, MonadIO) I was trying to confirm that it actually was the `deriving ... MonadState Bool ...` part that was causing the problem, and then I realized, it's not `MonadState Bool` I want, it's `MonadState t`. Upon changing that, everything compiles fine and ghc hums along happily. Should I still submit a bug report for a bad error message? /Joe On Nov 12, 2009, at 12:58 PM, Joe Fredette wrote:
Okay, so -- I feel totally awesome -- I never found a GHC bug before... and a Haskell Celebrity responded to my post! *swoons* :)
Serious question now, There's a fair amount of definitely irrelevant code (like the definition of the `Email` type, etc), should I post that in the report too (assuming it doesn't work in 6.12 or I can't get 6.12 working to try it)?
Thanks,
/Joe
On Nov 12, 2009, at 4:07 AM, Simon Peyton-Jones wrote:
| [1 of 3] Compiling Network.HackMail.Email.ParseEmail ( Network/ | HackMail/Email/ParseEmail.hs, interpreted ) | [2 of 3] Compiling Network.HackMail.Email.Email ( Network/HackMail/ | Email/Email.hs, interpreted ) | [3 of 3] Compiling Network.HackMail.Filter.Filter ( Network/ HackMail/ | Filter/Filter.hs, interpreted ) | *** Exception: No match in record selector Var.tcTyVarDetails
This is a bug in GHC without a doubt.
It's possible that it's fixed in 6.12 -- can you try the release candidate? If it is not fixed, or if it's too hard for you to try, can you submit a Trac bug report please? (Include your code, and instructions for how to reproduce.
Thanks
Simon