If you presume the user knows the type of (+) which I think is kind of fair. Ideally though it would be: (+) has no instance for (Num [Integer]) The the

If you presume the user knows the type of (+) which I think is kind of fair. Ideally though it would be: (+) has no instance for (Num [Integer]) The the improvement the GHC team made is already huge for those that have at least heard of Num, which I'd guess is anyone who's went through a Haskell tutorial.