Christian, This did the trick for me when I built Happy (just yesterday): LALR.lhs: change line 24 from > import Data.Array hiding (bounds) into > import Data.Array ProduceCode.lhs: change line 31 from > marray_indices a = Data.Array.MArray.indices a into > marray_indices a = range (bounds a) That should make you(r) Happy again. ;) HTH, Stefan