You create a module simply by starting your program code with a module/1 directive. This should usually be placed at the beginning of the source file and looks like
As a rule, the module name should be chosen to be the same as the file’s base name (the file name without directory/folder and suffix/extension part). For example, the module mymodule might be contained in a file mymodule.ecl.
Anything you define in your module is by default local to that module.
A definition is made available to the outside world by exporting it. All the exports of a module together form the module’s interface. Exporting is done with the export/1 directive, which can take different forms depending on the kind of the exported item.
Predicates are exported as follows:
:- export p/2. p(X,Y) :- ...
Structures are exported by defining them with an export/1 instead of a local/1 directive, e.g.,
:- export struct(book(author,title,publisher)).
And the same holds for operators and other syntax settings:
:- export op(500, xfx, before). :- export chtab(0'$, lower_case). :- export syntax_option(no_array_subscripts). :- export macro(pretty/1, tr_pretty/2, ).
All these declarations are valid locally in the module where they appear and in every module that imports them.
Initialization goals are exported as follows:
:- export initialization(writeln("I have been imported")).
Unlike the other declarations above, an exported initialization/1 directive is not executed locally in they module where it appears, but only in the context of the module where it gets imported.1
In order to use a definition that has been exported elsewhere, it has to be imported. Often it is desirable to import another module’s interface as a whole, i.e., everything it exports. This is achieved by an import/1 directive of the form
:- import amodule.
If the module is in a file and has to be compiled first, then use_module/1 can be used, which is a combination of ensure_loaded/1 (see chapter 6) and import/1:
If the module is a library in one of ECLiPSe’s library directories, then it can be loaded and imported by
or simply using lib/1 as in
It is also possible to import only a part of another module’s interface, using an import-from directive
:- import p/2 from amodule.
Note that this is the only form of import that can refer to a module that has not yet been loaded, and therefore allows a restricted form of circularity in the import structure.
For a given predicate name and arity the following rules hold: