[Haskell-beginners] better way to create Array defined on all indices

I'd like to have an Array indices values (see http://haskell.org/onlinereport/array.html) defined on [minBound::indices ... maxBound::indices]. The attached does this; however, it also allows duplicate definitions (e.g. in the attached, the value for Term index is defined twice). Is there a better way to do this? Maybe a way that doesn't use all the contexts? Also, is there a way to do it so that the value associated with an index is not redefined? In effect, I'm making a map, but using an Array as the implementation because, I guess, it would be a bit faster. TIA.