> The Visitor pattern mostly addresses the shortcomings of the type system (i.e no "match" statement).
The visitor pattern addresses doing multiple dispatch in a single dispatch language.
> The Command pattern, in its most basic form, could also be considered as implementing 1st class functions by wrapping them into objects.
BTW, that's not really true; first class functions are not a replacement for commands. Commands are about turning behavior into state so it can be stored and executed, potentially replayed for example, at a later time. Commands aren't just functions, even languages that have first class functions still use the OO command pattern when doing things that benefit from command patterns.
> Commands are about turning behavior into state so it can be stored and executed, potentially replayed for example, at a later time.
First-class functions plus partial application do that trivially. (First-class functions provide the ability to store a generic command, partial application let's you get a specific instance with local state that can be “replayed” against a different external state object.)
Again, you're missing the point of the command pattern. It is not replaceable by a first class function. I'm well aware of what first class functions are, what they can and can't do, and yes in the most trivial cases at run-time only where only a single action is required of the command, they can be used instead of a command pattern.
Many times commands come with multiple actions, to allow execution and rollback, require being able to be serialized to disk to database and replayed later, or are used to better organize and plug in extension commands to large code bases. None of these cases are amenable to first class functions.
The command pattern isn't just a hack around not having first class functions, we still use command even when first class functions are available. You aren't going to extend Photoshop with a new filter using a first class function; you're going to write a plugin which is a command pattern for filter execution.
Stop trying to tell me what first class functions can do, I'm fully aware, I use them every day and have for nearly 20 years. You aren't talking to some kid who never heard of functional programming.
The visitor pattern addresses doing multiple dispatch in a single dispatch language.
> The Command pattern, in its most basic form, could also be considered as implementing 1st class functions by wrapping them into objects.
BTW, that's not really true; first class functions are not a replacement for commands. Commands are about turning behavior into state so it can be stored and executed, potentially replayed for example, at a later time. Commands aren't just functions, even languages that have first class functions still use the OO command pattern when doing things that benefit from command patterns.