Jeff φ wrote:
However, my implementation of SmartArray requires me to create an instance of a selector class to tell the compiler whether the type is boxed or unboxed. I'm hoping to avoid creating instances of the selector class for every possible type. I'd be grateful for any suggestions.
Using ghc-6.8.2 I get test.hs:30:0: Functional dependencies conflict between instance declarations: instance [overlap ok] SmartArraySelector UArray Bool -- Defined at test.hs:30:0-46 instance [overlap ok] SmartArraySelector Array e -- Defined at test.hs:49:0-40 [more of the same for the other classes omitted] The offending lines are instance SmartArraySelector UArray Bool where vs. instance SmartArraySelector Array e where Note that it explicitly says 'overlap ok' but the functional dependencies cannot be fulfilled. You defined class (IArray a e) => SmartArraySelector a e | e -> a Your generic instance says that it determines the 'a' type for /all/ types 'e' as 'Array'. This conflicts with the other instance which says it determines the 'a' for the specific type 'Bool' as 'UArray'. That leaves the question how to achieve what you want, for which unfortunately I have no answer. Cheers Ben