module - encapsulate MATLAB package into a name space module

This function encapsulates a package directory into a module, simplifying
function access without altering the MATLAB path. To understand how
modules are useful, consider the following multi-directory project.
./main.m % main routine
./+GUI % graphical user interface package (functions A, B, ...)
./+GUI/+graphics % low level graphics package (functions 1, 2, ...)
Package functions are normally accessed with a prefix:
[...]=GUI.functionA(...); % function A in GUI package
[...]=GUI.functionB(...); % function B in GUI package
[...]=GUI.graphics.function1(...); % function 1 in graphics sub-package
[...]=GUI.graphics.function2(...); % function 2 in graphics sub-package
indicating where the function resides with respect to the top of the
package (highest directory that starts with a '+'). Prefixes are fine
for top-down access (though they can become quite long) and can be
eliminated with MATLAB's "import" function, although importing a package
can create name space confusion without warning. The bigger problem is
that prefixes are required for function calls at the same level. For
example, functionA must access functionB as 'GUI.functionB' (or import
the GUI package); similiarly, function1 must access function2 as
'GUI.graphics.function2'. This requirement makes it difficult to use
standardized libraries in user-developed packages because intra-library
calls must be modified manually. Package tree revisions are particularly
difficult, requiring manual corrections throughout the project.

Modules avoid this unpleasantness by storing functions as handles inside
a structure. For example, the following code loads the GUI package into
a module called 'local' for use in the main routine.
local=module('GUI'); % use this from functions in ./
[...]=local.functionA(...);
Sub-packages can also be accessed.
local2=module('GUI.graphics');
[...]=local2.function1(...);
Module definitions are location specific. The following code illustrates
accessing the graphics package from inside the GUI package.
graphics=module('graphics'); % use this from functions in ./+GUI
[...]=graphics.function1(...);
When no package is specified, the module is created where it is called.
This permits function1 to access function2 without knowing anything about
higher package levels.
name=module(); % access calling function's directory (*)
[...]=name.function2(...);
This last example seems trivial, but MATLAB's implementation of packages
breaks the traditional rule where functions can see other functions
inside the same directory.
(*) Modules defined without an explicit package name reference the lowest
entry point of the package hierarchy, skipping class directories.

Some upfront effort is needed to use modules, so it is recommended only
for large projects. Behind the scenes, modules are merely automatic
constructions of the package prefix, and as such all features that
support packages (such as classes) should work within modules. Remember,
modules are only valid as long as the top package is visible to MATLAB!
In the preceeding examples, this means the directory containing 'main.m'
and +GUI must be on the MATLAB path

For situations where similar modules are constantly being created, such
as graphical user interfaces, it *might* be worthwhile to create
persistent modules:
function some_function(varargin)
persistent name
if isempty(name)
name=module;
end
or use global modules where necessary (standard warnings apply).
Finally, all calls to package functions should use parenthesis:
module_name.function_name(); % always use parenthesis!
even if the underlying function has no inputs. Omitting the parenthesis
will return the function handle instead of evaluating the function.