As a previous C++ and Erlang programmer, polymorphism on return type was the hardest thing for me to internalize. Like, I could repeat the words, but I didn't "

As a previous C++ and Erlang programmer, polymorphism on return type was the hardest thing for me to internalize. Like, I could repeat the words, but I didn't "grok" it for the longest time. I wish there was some standard way of emphasizing this. (Might help with the Monad tutorial jungle, too, as that's the implementation linchpin)