Resolving dependencies...
Configuring exceptional-0.1.2.0...
Building exceptional-0.1.2.0...
Preprocessing library exceptional-0.1.2.0...
[1 of 1] Compiling Control.Exceptional ( Control/Exceptional.hs, dist/build/Control/Exceptional.o )

Control/Exceptional.hs:45:24:
    Couldn't match expected type ‘Either String a’
                with actual type ‘Exceptional a’
    Relevant bindings include
      x :: a (bound at Control/Exceptional.hs:45:19)
      toEither :: Exceptional a -> Either String a
        (bound at Control/Exceptional.hs:44:1)
    In the expression: Success x
    In an equation for ‘toEither’: toEither (Success x) = Success x
Failed to install exceptional-0.1.2.0
cabal: Error: some packages failed to install:
exceptional-0.1.2.0 failed during the building phase. The exception was:
ExitFailure 1