Mathematics and Computation

I have added another language, called Boa, to the Programming Languages Zoo. It is an object-oriented language with the following features:

• integers and booleans as base types,
• first-class functions,
• dynamically typed,
• objects are extensible records with mutable fields,
• there are no classes, instead we can define “prototype” objects and extend them
  to create instances.

In many respects the language is a bit like a combination of Python and Javascript, which explains its name. It was interesting to see the students’ reaction to the language. The only object-oriented language they knew previously was java, so the lack of classes bothered them. They were amused by the fact that since “everything is an object” we can extend an integer with a function to get an object which behaves both as an integer and as a function (we did not learn about intersection types), like this:

Boa> let x = 42 with (fun x -> x + 1000)
x = 42 with <fun>
Boa> x + 10
52
Boa> x 17
1017
Boa> x x
1042

Isn’t that cute?