Re: Haskell Platform call for consensus: add transformers and revise the mtl package to depend on it

On Thu, Nov 04, 2010 at 08:36:24PM -0500, Jeremy Shaw wrote:

I intend to upload a new version of happstack 0.5 which has the proper constraints. And happstack 6 will be migrated to transformers/monads-fd.

mtl-2.0.0.0 is now a copy of what monads-fd was, and monads-fd is now a deprecated stub re-exporting mtl-2.0.0.0. So you'll want to migrate to transformers/mtl-2. But in your case, on line 578 of src/Happstack/Server/SimpleHTTP.hs: getFilter m = WebT $ ErrorT $ fmap lft $ getFilter (runErrorT $ unWebT m) If you replace fmap with liftM, it will build with both old and new versions of the mtl package.