Example will not compile

[aleklisi]

https://docs.riak.com/riak/kv/2.0.4/developing/app-guide/advanced-mapreduce/#reduce-function-examples
This

fun(ValueList, _Arg) ->
  [lists:foldl(fun erlang:'+'/2, 0, List)]
end.

will not compile, because List is unbound. Unless List is defined somewhere prior, but since it is not written, I assume it is not.
It should look like this:

fun(ValueList, _Arg) ->
  [lists:foldl(fun erlang:'+'/2, 0, ValueList)]
end.