# Modularity¶

Modularity is the essence of programming and the first line of offense against programs that threaten to become unwieldy. Avalon provides two simple tools to assist you in creating modular programs.

## The import statement¶

The first thing to do is to spread a program into separate files so as to avoid having one huge monolithic program. This is done by creating packages which are just files containing Avalon programs and ending with the extension .avl like any other Avalon program.

Let us consider that one has created a package localed at ./stdlib/algorithms.avl then this package can be imported by using the following:

-- every public declaration inside the package can be used after a successful import
import stdlib.algorithms


## Namespaces¶

Even after we have separated programs into small manageable packages, there is still the threat of name collision. This is resolved by using namespaces. Namespaces allow the same name to be used in two packages without colliding so long as that name happens to be in two different packages. Of course, if the same name is reused twice in the same namespace in two different packages that are imported simultaneously, a collision wil occur. It is thus the responsibility of the programmer to manage their namespace to avoid name collisions.

A namespace is created by the following syntax.

-- import statements must figure outisde of a namespace
import io

-- your namespace declarations go here
namespace Ns -/
-- type declarations come here

-- global variables come here

-- function declarations come here
/-

-- you can have two namespaces in the same package
namespace Wh -/

/-


Attention

Import statements must occur outside of namespace declarations.

Note

You can have two namespaces in the same package.

Tip

You can choose to indent the declarations inside a namespace (or not).

One might ask what happens when we don’t declare a namespace. If no namespace is provided, then all your declarations go into the global namespace which is the namespace without a name.

-- the global namespace
-- this is the same as not declaring a namespace at all
namespace -/
/-


Note

The __main__ function must always occur in the global namespace.

Attention

As a convection, namespace names are in PascalCase. This is not enforced by the compiler but makes for very readable code.

### Using declarations inside a namespace¶

A declaration inside a namespace is used by preprending it with the namespace name. Imagine the Io namespace that contain the println function. To use this function, one does the following:

import io
import math

-[ <namespace>.<declaration> is how a namespaced declaration is used ]-

-- using a namespaced function
Io.println("Hello World!")

-- using a namespaced variable
Math.PI