The one-letter variables are all type parameters, and pretty much every programming language uses one-letter variables for type parameters. And I can't think of a better syntax for "functions from a to b" than (a → b). In a Java-ish syntax it'd look like:

    interface Functor {
        <T, U> Self<U> fmap(Self<T>, Function<T, U>);
    }

which is just torture. What would it look like in your ideal syntax?

Give the types useful names, like everything else. Recently I did a review for a new peer and was pleasantly surprised that they used proper names for generic arguments. At first I stumbled of course, because I wasn't used to generic arguments being longer than a few characters but I think it helped the readability a lot.

    interface Functor {
        <Source, Target> Self<Target> fmap(Self<Source>, Function<Source, Target>);
    }

Same code, but you get an additional hint of what's going on.

Alright, that's fine, but the person I replied to was complaining that "Haskell folks love arrows and one letter variable names", and my point was that most programmers love one letter variable names in this context.