mtl library in HEAD?

Kathleen Fisher kathleen.fisher at
Thu Sep 2 18:20:56 EDT 2010

Got it working.  Thanks!

On Sep 2, 2010, at 12:44 AM, Don Stewart wrote:

> malcolm.wallace:
>>> The library installs fine with earlier versions of Haskell.  Is there 
>>> something wrong with my installation, or is this a new  
>>> incompatibility?  If the latter, is a corrected version of the mtl  
>>> library going to be available soon?  Alternatively, how can I fix it?
>> Yes, this is a new incompatibility.  The instance in question recently  
>> moved from the mtl package to the base package, after discussion on this 
>> list.
>> Until the next release of ghc/base/mtl, it will be necessary to use the 
>> HEAD versions of all of them (not merely the HEAD of ghc).
> And indeed ,the inverse patch has been applied to mtl,
>    Fri Jul 30 17:40:34 CEST 2010  Ross Paterson <ross at>
>      *  move Monad and MonadFix instances for Either to base (proposal #4159)
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