Declaring

Namespaces are a programming language construction that allows us to package related definitions together. A canonical example of a namespace is a data type and associated operations over it (e.g. stacks or queues). The rest of the program can access these definitions in a regular way, providing maintainability, reusability and safety.

By contrast, a record cannot package type definitions together with values: namespaces can, but records are values and namespaces are not values: this is where design comes into play: do we want to create a kind of library, which we use for other tasks, or do we want to compute? If the former, we would probably use a namespace; if the latter, an record.

For a concrete example, we could create a namespace that packages a type that represents amounts in a particular currency together with functions that manipulate these amounts: constants, addition, subtraction, etc.

Namespaces are introduced using the keyword namespace, and type and value definitions are grouped within a block opened by "{" and closed by "}". Namespace names must start with a capital letter.

For example, the following code defines a module Euro that packages together a type, called t, together with an operation add that sums two values of the given currency, as well as coins for one and two euros.

namespace Euro {

export type t = nat;

export const add = (a: t, b: t) : t => a + b;

export const one: t = 1n;

export const two: t = 2n;

};

In this example you will also notice how all definitions are prefixed by the keyword export: this enables access to them from outside the namespace.