"Depending on the context, the idea of a hash table with a prototype may be a contradiction in terms. For instance, if by "hash table" we refer to exactly the hash table implementation Racket has today, then it simply has no prototypes. :-p
There are contexts where it does make sense, particularly when talking about hypothetical languages, but if a single language tried to make sense of every idea people had for it, it'd be pretty darn bloated. ^_^"
How so? JavaScript and Lua both add prototypes to tables/objects. It's possible to implement it in Arc right now, it's just not possible to make them blend seamlessly into the language, which is one thing I plan to fix with Arubic.
A prototype isn't defined by it's implementation, it's defined by it's idea. You could define an alist or plist to be a prototype, or an AVL tree, or who knows what else. Heck, I was using functions to represent prototypes earlier. :P There are only two requirements for prototypes in my mind: message passing, and, when data is not found in the data structure, it will check it's parent rather than failing[1].
To put it another way, you can use delegation and message passing to implement the concept of prototypes. And since we're talking about Arubic here, I can implement prototypes with just about any compound data type. :P
So when I mentioned prototypes, I was referring to the fact that it is indeed possible to give inheritance to hash tables, and so although you're right that structs are not the same as hash tables (at least in Racket), I'm pointing out that they could be the same, which is the direction I'm going in Arubic.
Actually, you could probably treat hash tables as prototypes in Racket too, but you would need to use special functions to access them:
(proto-get foo 'bar)
(proto-set foo 'bar 'qux)
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"Actually, they do. A Racket struct can implement the 'prop:procedure structure type property to specify how it should behave when called like a procedure.
In fact, it can also implement 'prop:dict to behave like a dictionary. Hash tables and association lists are other things that can be used as dictionaries."
Ah, I see, so it's basically a bigger and more complicated version of the message passing in Arubic. I still prefer Arubic. :P
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* [1]: Technically speaking, you could implement prototypes by copying the data, rather than using delegation... but when I refer to prototypes, it is referring to the delegation-based model, as that's what JavaScript and Lua use.
Also, I do draw a distinction between classes and prototypes, even though both use message passing and inheritance. The distinction isn't a very huge one, though. Instances inherit from a class, and a class inherits from other classes. Interestingly enough, it's possible to emulate classes using prototypes, but not possible to emulate prototypes using (static) classes... thus you could say that prototypes are a superset of classes.
It is possible to emulate prototypes in a language with dynamic classes though, like Python. It just requires you to create a new class at runtime, then create a new instance. So every class would have precisely one instance. This is still kinda kludgy, though... for instance, Python requires some special properties to be defined on classes... you can't add them to instances.
