.. _section-Built-in Libraries and Types, Modules, and XSB predicates:

Built-in Libraries and Types, Modules, and XSB predicates
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We have already encountered some built-in types, like \\date and \\boolean. Flora also has a number of built-in operations on these types. The full list of built-in types and the operations on them can be found in the chapter “Primitive Data Types” in the Flora-2 manual [#Flora2-Manual]_. It is worthwhile to familiarize yourself with this chapter. For example, to get the year component out of a \\date object, one can do:

.. code-block:: flora

    ?date[ year -> ?year ]@\basetype

The @ operator tells Flora that the property is defined in a *module*, whose name follows the @. All operations on the built-in types are found in the \\basetype module. The @\ *module* syntax should follow directly after the frame.

All Flora content is contained in a module. A module is a runtime or in-memory notion; not a file-based notion. A file (or statement) can be loaded into different modules at runtime. By default, the “main” module is used. It is possible for a user to define other modules. We have generally found this to be more problematic than useful, and module support is not heavily tested in **Sunflower**. We recommend not defining your own modules, and thus only using the @ syntax to call pre-defined modules.

Besides the \\basetype module, two other modules are good to know about: \\io and \\prolog.

The \\io module, as its name implies, allows you to do to certain I/O operations. One common use of it is to print text to the console, as debugging statements inside rules. For example,

.. code-block:: flora

    ?Person [ thirdCousin -> ?ThirdCousin ] :-
      ?Person [ grandparent -> ?Grandparent1 ] \and
      ?ThirdCousin [ grandparent -> ?Grandparent2 ] \and
      fmt_write('checking whether %S is %S\s first cousin\n',
       f2(?Grandparent2,?Grandparent1))@\io,
      ?Grandparent1 [ firstCousin -> ?Grandparent2].

The f2 function is an arbitrary function symbol needed to contain the arguments to fmt\_write. Note that Flora produces a warning if you use e.g. f everywhere, with different numbers of arguments. Therefore, we tend to use f followed by the number of arguments, such as f2 for a two-argument container in this case. See the chapter “Flora-2 System Modules” in the Flora-2 manual [#Flora2-Manual]_ for more details.

Finally, the \\prolog module allows you to call XSB predicates from Flora. This opens up the use of XSB’s (more extensive) built-in library. See the section “Calling Prolog from Flora-2” in the Flora-2 manual [#Flora2-Manual]_, and the XSB manual [#XSB-Manual]_ for the list of XSB’s built-in predicates. However, we recommend using Flora predicates whenever possible. For most users, there should be no need to call XSB predicates.


.. [#Flora2-Manual] Kifer, Michael, Guizhen Yang, Wan Hui, and Chang Zhao. 2014. *Flora-2: User's Manual*. 1.0. Stony Brook University, Stony Brook: Department of Computer Science.



.. [#XSB-Manual] Sagonas, K, Terrance Swift, David S Warren, Juliana Freire, Prasad Rao, Hassan Davulcu, and Steve Dawson. 1998. *The XSB Programmer's Manual (Version 1.8)*. Stony Brook, NY: Department of Computer Science, SUNY at Stony Brook.