make it build with versions of base before and after 4.3
authorRoss Paterson <ross@soi.city.ac.uk>
Fri, 3 Sep 2010 11:33:58 +0000 (11:33 +0000)
committerRoss Paterson <ross@soi.city.ac.uk>
Fri, 3 Sep 2010 11:33:58 +0000 (11:33 +0000)
commit64b7aa5d518419f79f2406835f2e6d7eb358d2da
tree217eb67245f42d823474a63fbf08540965d8092a
parentf8a26ee9666c9c5edfaa6f44e4a73aa2c528852b
make it build with versions of base before and after 4.3

The Monad and MonadFix instances for Either moved to base-4.3, and
lost their Error constraints.  Test the version of base to either
supply the instances here or use the ones from base.
Control/Monad/Error.hs
mtl.cabal