Organizing modules in packages

Modules to be imported can be grouped in packages.

Package basics

Structuring your sources is important for maintenance, readability, reusability and deployment.

Modules can be grouped by packages, based on the directory structure of source files. A source tree starts at a top-dir, with package sub-directories containing modules:

top-dir/
|-- mylibs/                   -- package: mylibs
|   |-- myutils/              -- package: mylibs.myutils
|   |   |-- fileutils.4gl
|   |   |-- sqlutils.4gl
|       ...
|-- webserv/                  -- package: webserv
|   |-- stock.4gl
|   |-- shipment.4gl
|       ...
... 
|-- starter.4gl               -- main programs
|-- reports.4gl

A sequence of directories defines a package-path. In a package-path, package names are separated by a dot. In the above structure, the package-path "mylibs.myutils" corresponds to the directory path "mylibs/myutils", relative to "top-dir".

Use simple regular identifiers for package and module names, using ASCII characters. Do not use names such as "1mod", "forêt", "module-1.4gl".

Declaring a module for a package

In order to indicate that a module belongs to a package, use the PACKAGE instruction at the top of the module source.

In the following example, the module fileutils.4gl is declared as a module of the mylibs.myutils package:

PACKAGE mylibs.myutils

PUBLIC FUNCTION getSubDirs(path STRING) RETURNS ...
    ...
END FUNCTION

Importing package modules

Importing a module from a package is achieved by specifying the package-path in the IMPORT FGL instruction, followed by a dot and the module name:

IMPORT FGL mylibs.myutils.fileutils

PUBLIC FUNCTION file_browser(defpath STRING) RETURNS (INTEGER,STRING)
    DEFINE dirs DYNAMIC ARRAY OF STRING
    CALL mylibs.myutils.fileutils.getSubDirs(defpath) RETURNING dirs
    ...
END FUNCTION

The package name specified after IMPORT FGL is a package-path, that must reflect the directory path based on the top-dir of the sources, using dots as separators. For example, to import the "fileutils" module from the top-dir/mylibs/myutils directory, use:

IMPORT FGL mylibs.myutils.fileutils

All modules of a package can be imported by using the .* syntax:

IMPORT FGL mylibs.myutils.*

When a module under a package wants to import a sibling module, specify the full package-path in IMPORT FGL:

This is fileutils.4gl, from the mylibs.myutils package, in top-dir/mylibs/myutils:

PACKAGE mylibs.myutils

PUBLIC FUNCTION getSubDirs(path STRING) RETURNS ...
    ...
END FUNCTION

This is sqlutils.4gl, from the same mylibs.myutils package/directory:

PACKAGE mylibs.myutils

IMPORT FGL mylibs.myutils.fileutils

PUBLIC FUNCTION findConfigFile(path STRING) RETURNS STRING
    ...
    CALL mylibs.myutils.fileutils.getSubDirs("/opt/myapp") RETURNING ...
    ...
END FUNCTION

Module aliases

To simplify the source code when a package-path is long, define module aliases with the AS keyword:

IMPORT FGL mylibs.myutils.fileutils AS fu
...
    CALL fu.getSubDirs(defpath) RETURNING dirs

Note that the alias provided with IMPORT FGL … AS … is a module alias. There is no way to define a package-path alias.

Finding modules with FGLLDPATH

For compilation and at runtime, a root-path defined in the FGLLDPATH environment variable will be used to find a package module as root-path/package-path/module-name[.4gl|.42m].

FGLLDPATH typically contains the top-dir of the package path.

For example, with the following package/directory structure:

top-dir/
|-- mylibs/
|   |-- myutils/
|   |   |-- fileutils.4gl
|   |   |-- sqlutils.4gl
|-- app1/
|   |-- main.4gl

FGLLDPATH can be defined to top-dir, to find modules from the mylibs.myutils package, when compiling main.4gl in the app1 directory:

$ cd top-dir
$ export FGLLDPATH=$PWD
$ cd app1
$ fglcomp -M --verbose main.4gl
[parsing top-dir/mylibs/myutils/fileutils.4gl]
[building mylibs/myutils/fileutils]
[writing top-dir/mylibs/myutils/fileutils.42m]
[parsing top-dir/mylibs/myutils/sqlutils.4gl]
[building mylibs/myutils/sqlutils]
[writing top-dir/mylibs/myutils/sqlutils.42m]
[parsing main.4gl]
[building main]
[writing main.42m]