Modules

A namespace is a set of functions or scripts that can "see" the same objects.

In Julia, namespaces are created by modules.

A module is created by

julia> module Foo
            export g
         f(x) = x ^ 2;
            g(x) = x / 2;
       end
Main.Foo

Even what you run in the REPL lives in a module called Main.

This is why the module that we just created is Main.Foo (not just Foo).

It is a sub-module of Main.

To access the objects inside of Foo we need to import the module:

# We did not import `Foo`, so we get an error.
julia> f(2)
ERROR: UndefVarError: f not defined
Stacktrace:
 [1] top-level scope at REPL[3]:1

# This imports `Foo`
julia> using .Foo
julia> Foo.f(2)
4

We still cannot just type f(2) because Foo did not export f

Only objects that are exported can be called without the module name as a qualifier.

julia> g(2)
1

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