Re: [Haskell-cafe] Library for overloaded indexing (a la (!))

However, the purpose of this was for syntactic simplicity, which I think it's hard to argue Lens provides in this case. "^? ix" isn't exactly user-friendly, and it only provides a substitute for "!?", not "!". (Or at least, I couldn't figure out how to get "!" behavior cleanly.)

Look at the type: [1,2,3,4] ^. ix 2 :: (Num a, Monoid a) => a It typechecks, but the result must be a Monoid that has a Num instance. There are Product and Sum wrappers for Num (because the identity element can be either 0 or 1, depending on mappend, which can be + or *). So, this works fine: getSum $ [1,2,3,4] ^. ix 2 => 3 getSum $ [1,2,3,4] ^. ix 42 => 0