oopThere are three things in EO (and the 𝜑-calculus which we based it on): data, atoms, and objects. There is a dataization function, which puts all three together in order to make an EO program alive. Here is how it works together with Java, for example.
Let’s say we are making an online shop where items are being shipped to different countries and we must calculate shipment costs based on the customer’s location. We create an abstract object that represents shipment costs:
[customer] > cost-of-shipment
if. > @
customer.country.eq "US"
9.99
24.99
Then, let’s say we have an abstract object customer-in-mysql, which represents the customer’s information in the MySQL database. To make a specific customer jeff we make a copy of customer-in-mysql, specifying the ID of the customer as 42:
customer-in-mysql 42 > jeff
The closed object jeff is the customer we are looking for. We assume that it has the country child object, which is needed by the cost-of-shipment.
Now, we make a copy of the cost-of-shipment and then add it to the product price in order to calculate how much a customer has to pay:
cost-of-shipment jeff > x
x.add > total
product.price
Here, the x is a new object, a copy of cost-of-shipment. Then, we take the child abstract object add from it and make a copy, giving product.price object to it as an attribute. We name the created copy as total. Then, we print the total price:
QQ.io.stdout > app
QQ.txt.sprintf
"Your total is %f" total
All these manipulations don’t make the number print yet. They are all object declarations. We’ve declared one abstract object cost-of-shipment and a few closed objects: jeff, x, total and app.
Now the most interesting part, which we call dataization. It’s a process of turning an object into data. The data is something that doesn’t have any child objects and is the simplest element of the computing platform, where EO software is being compiled. You may think that in the example above 42 and "US" are data. They are not. They are also objects and we can write this, for example:
42.add 5 > z
"US".length > len
The data behind these objects is not visible for us at the level of EO program. The data is inside the 42 object. Only the runtime of the specific platform can dig it out through the dataization mechanism. If you compile the EO code to Java, you will get a class EOapp (derived from the app object), which can be dataized like this:
import org.eolang.phi.Data;
EOapp app = new EOapp();
Boolean data = new Dataized(app).take(Boolean.class);
The method take() will take the object app and will try to ask it to turn itself as data. The object stdout will redirect this request to the object sprintf, which will ask the object total the same thing: what data do you have? The object total is the object x.add. If we look at what x is, we’ll see that it’s a copy of our own abstract object cost-of-shipment, which doesn’t have the child object add! However, it does have a child object @, which is a “catch-all” object: the request to get add will land there.
The object bound to the attribute @ is the copy of if:
if. > @
customer.country.eq "US"
9.99
24.99
It will take the customer.country.eq, dataize it in order to get boolean data, and then, depending on this data, return either 9.99 or 24.99. Either one of them has the attribute add, which will be used to construct a new object, with an argument product.price. The result will be used by the Dataized Java class in order to continue the process of dataization. Finally, the sum of two numbers will be dataized to a Java floating-point number.
The dataization of customer.country.eq is happening inside the runtime and is not visible at the level of EO. The object eq is called an atom, since it’s an atomic element of the language—it has to be implemented in Java, not in EO. There are other atoms in the example above: if, sprintf, add, stdout, and length. They all are implemented in Java.
Thus, we construct objects first, either through abstraction (declaring new abstract objects) or through application (making copies of abstract objects). Next, we dataize one of the objects and the entire composition of objects starts to “live,” trying to turn itself into data.
