What to do to make use of the calculus module in a new command-line tool.


§1. Status. The calculus module provided as one of the "services" suite of modules, which means that it was built with a view to potential incorporation in multiple tools.

By convention, the modules considered as "services" have no dependencies on other modules except for foundation and other "services" modules.

§2. Importing the module. We'll use the term "parent" to mean the tool which is importing calculus, that is, which will include its code and be able to use it. As with any imported module,

Import: somepath/calculus

§3. Using callbacks. Shared modules like this one are tweaked in behaviour by defining "callback functions". This means that the parent might provide a function of its own which would answer a question put to it by the module, or take some action on behalf of the module: it's a callback in the sense that the parent is normally calling the module, but then the module calls the parent back to ask for data or action.

The parent must indicate which function to use by defining a constant with a specific name as being equal to that function's name. A fictional example would be

    @d EXPRESS_SURPRISE_CALCULUS_CALLBACK Emotions::zowie

    =
    void Emotions::zowie(text_stream *OUT) {
        WRITE("Zowie!\n");
    }

The calculus module has only a few callbacks and all are optional. The following alphabetical list has references to fuller explanations:

§4. In addition, the following value can optionally be defined: