The World and the Court.

The world inside hwut is a database of variables, passed events, functions, and event handlers. It exists in paralell to the test. It’s state is maintained by events and variables. Events float into the world from the application. Variables are set and adapted as a consequence of rules. The rules are maintained inside the court. The rules are defined in a language called ‘Joy’ which is explained in the following paragraphs.

In Joy information is processed in terms of objects, operations, and control structures. There are two types of objects: Events and variables. Events are objects that appear at a certain time and trigger a court review. A court review goes through all active rules and may detect broken rules. Variables maintain data. The data may be plain passive data such as names or numbers, but may also be functions. To help to maintain data, container types for lists and dictionaries are also available. The following enumeration provides a short overview over variable types.

Numbers

Numbers can be specified in decimal, hexadecimal if preceeded by 0x, octal if preceeded by 0o, or binary if preceeded by 0b. Only decimal numbers can be used as floating point numbers. Example:

x = 0b1000.1010;    # Assign 0x8A to variable x
z = 0o777;          # Assign 0x1FF to variable z
y = 0x4711;

Boolean

The keywords true and false may be used to describe boolean constants. Example:

x = true;
y = false;

Strings

Strings are specified by their traditional quote bracketting, such as in "hello world!".

x = “This is a string”;

Lists

A list is a data container that stores objects in a sequence. Objects in the sequence can be addressed only by iteration or (position) index. A list is specified by a comma seperated list in ‘[‘ ‘]’ brackets. Example:

x = [1, 2, 3];
y = [];

List have member functions which help to operate on them, as they are

.pop() .insert() .size() .count() .delete()

Elements of lists can be iterated over in ‘for in’ expressions or accessed via the index, such as in

x = my_list[23];

which accesses element ‘23’ in my_list.

Maps

A map is a data container that can match a string, a boolean, or a number to another object. That is, objects are refered to by a key (string, boolean, or number). Example:

x = { "Otto": 17, "Fritz": 12, };

Elements in maps can be accessed with the same operator, i.e.:

x = my_map["Otto"];

catches what is associated with “Otto” from the map.

There are special variables in the world starting with a dollar sign.

$INIT

$INIT is the event of initialization. It appears before any other event is processed. It is particularily useful to setup an initialization in the rules, such as:

on $INIT: {
     my_dict = {};
     error_n = 0;
     ...
}

The $INIT event appears minus one jiffy before zero time. By default this is -10e-6.

$time

$time which provides the current time. It may be used for conditions or to measure time spans, etc.

$time_alert

Inside a rule which is subject to ‘awake’ and ‘sleep’ the special variable $time_alert tells for how long the rule has been awake in a row.

Events can be referred to by their plain name. That is, if there is an event X sent from test application it can be referred to in the world as X. That is, if the test application reports an event:

0.123: TRIGGER;

then this event can be referred in the world as TRIGGER. An expression of an event name evaluates to true only at the exact instance when it occurrs. It evaluates to false at any other time. Adornments to events can either be accessed by indexing or by name. Example::

0.123: TRIGGER(x=12, y=13, label="line");

In the world, the adornments or members of TRIGGER can be accesssed by . followed by a member name. That is, TRIGGER.x, TRIGGER.y, and TRIGGER.label result in the contents 12, 13, and "line". Any event X in the database has three special members that can be accessed.

X.time

delivers the value of $time at the moment when the event occurred the last time.

X.count

gives the number of times that the event ‘X’ has occurred.

Events can be raised to have the meaning of state entries. This happens by means of the state_machine keyword, for example:

state_machine BED, HOME, WORK;

in TheDude example would define the state entries BED, HOME, and WORK. Once, this is done transition events can be referred. That is:

WORK->HOME;

referres to the instance in time when HOME is reported after WORK. The world does not get confused by other events which do not belong to the state machine, so that an event list reported as:

...
0.123: WORK;
0.153: COFFEE_SHOP;
0.231: GAS_STATION;
0.712: HOME;
...

would still trigger the transition event WORK->HOME, because COFFEE_SHOP and GAS_STATION do not belong to the same state machine. Behind the scenes the state_machine statement constructs an internal state machine, registers its admissible states and tracks the state transitions.