Rules¶

Rules result in verdicts and trigger changes to the world. Verdicts are a result of conditions and changes in the world are result of commands. This section first discusses the syntax of conditions and commands. Rules can be constraint in different ways by other condition which are discussed in section XXX. To collect rules in manageable units they can be located in name spaces which can be frozen and unfrozen. Name spaces are discussed in section YYY. To write more sophisticated tests HWUT provides data structures such as dictionaries and lists. The data structures together with functions are discussed in section ZZZ.

Condition

A condition maps the setting of variables of the world to a truth value of ‘true’ or ‘false’.

The syntax of conditions is oriented towards traditional conventions as they are set by C, Java and the like. That is, the operators > and >= stand for ‘greater’ and ‘greater or equal’, < and <= represent ‘lesser’ and ‘lesser or equal’. == stands for ‘is equal and != stands for not equal. Conditions can be grouped by the normal brackets ( and ). Mathematical operators such as +, -, *, /, and % (modulo) may be used at ease. The binary operators << and >> perform a left and right shift operation. x**y stands for x power y. ++x and x++ pre and post increment while --x x-- pre and post decrement.

Not so traditional, is the negation of a condition done by a prefix of not. Conditions can be combined by the boolean operators and and or. An expression A in B, where B is a list, is true if and only if A is an element of the list. If B is a dictionary, then the expression is true if and only if A is a key into the dictionary. A more deliberate discussion on lists and dictionaries in a later section. The and, or, not, and the in operator are in the style of Python.

The following shows a condition that combines some comparison operators in grouped conditions containing also the not and in operators.:

(x % 2 == 0) or (x in exceptions and not (name in ["Otto", "Fritz]))


An event name by itself means that the event has occurred. This condition is true if x is even (remainder of x/2 = 0), or it is in the list of exceptions and lesser than db_size. A condition is already a rule and produces a verdict of true or false. A single awake rule producing a verdict of false lets the test fail.

Command

A command sends an event to the world, changes the setting of its variables or writes some logging output.

The syntax to send an event, is simple. It requires the keyword send followed by the event description as explained in the previous section. For example:

send BUTTON(state="up", color="red");


sends an event called BUTTON along with its state variables state set to ‘up’ and color set to ‘red’. Another useful command is the print command. By means of this command additional information may be printed which may help to analyze why certain rules triggered or how they derived their verdict. For example:

print "slept_hour_n = ", slept_hour_n


will print the term slept_hour_n together with its value and a terminating ! to the trace, such as

... 53.000: << slept_hour_n = 4! >> ...

The print function cannot handle format strings. It is kept rather simple. Its purpose is to support debugging by the display of values which may be relevant to rules.

Scalar variables may be set or modified by the assignment operator = or its variants +=, -=, *=, /=, <<= assign left shifted, >>= assign right shifted, &= for assign logical and, |= for assign logical or, and ^= assign logical exclusive or. The following fragment shows some examples.:

x     = 0;
y    += y + (0x21 << 1);
speed = acceleration * (t**2);


Let us now define a first couple of rules for TheDude. For that, some syntax knowledge is pre-fetched, while its detailed discussion follows in later chapters. First, by using on we can constrain rules to the moment when an event occurs. Second, with once rules can be constraint to the moment when a condition becomes true. The if keyword signalizes an implication. That is, its consequences are executed if and only if its condition is true.

Let us assume, that TheDude should work at least five but never more than nine hours. His work place is only open from 7am to 5pm. Thus, TheDude shall not be in the state of WORK beyond these hours. We define:

on WORK: {
WORK.w >= 5 and WORK.w <= 9;              # work 5 to 9 hours
($time % 24 >= 7) and ($time % 24 <= 17); # office open: 7am-5pm
}


The curly brackets define a list of conditions. Since it follows on WORK: it is only evaluated at the moment when the event WORK appears. Then, this fragment checks whether the accumulated amount of work complies to its limits and if the global time is in the borders of the office time. The % operator is used to get the time in the frame of one day. Let us now specify that TheDude shall sleep at least 5 hours each night.:

once $time % 24 > 7: { # Night is over. print "7o'clock: slept_hour_n = ", slept_hour_n, ";"; slept_hour_n >= 6; # He must have slept 5 hours. slept_hour_n = 0; # Reset } once$time % 6 == 0:
# Every six hours print the day time.
print "Day time = ", $time % 24, ";"; on BED: if ($time % 24 > 20) or ($time % 24 < 7): # Night slept_hour_n += 1;  That is, when it is seven o’clock in the morning, we check whether five hours of sleep have been accumulated. During the night, from 8pm to 7pm in the morning each hour the slept_hour_n is incremented by one when TheDude is in BED. Rules are totally independent of the programming language of the unit under test. It is HWUT’s own little language to describe temporal logic rules. Assumed that the former rules are stored in dude.tlr (extension ‘.tlr’ for temporal logic rules) the first HWUT test file can be finalized. The example usage program must be extended with a response to --hwut-info as a command line argument. The Perl test program becomes #! /usr/bin/env perl use TheDude; if( "--hwut-info" == shift ) { printf("TheDude: Temporal Logic Tests;\n"); printf("LOGIC: dude.tlr;\n"); exit; }$joe = TheDude::new();
for($time=0;$time < 1000; ++$time) { if( TheDude::on_clock($joe, $time) ) { printf("%02i: BUZZ!\n",$time % 24);
}
printf("%02i: %s(nfs=%0.1f, w=%s);\n", $time % 24,$joe->{state}, $joe->{need_for_sleep},$joe->{work_time});
}


If the test is stored in test.pl, a call on the command line

> hwut ld test.pl

lets HWUT perform its temporal logic test and display the traces on the screen. The above example, delivers:

0.000000: BED(nfs=4.0, w=0.0)
0.000000: << Day time = 0.0; slept_hour_n = 1.0; >>
1.000000: BED(nfs=3.0, w=0.0)
2.000000: BED(nfs=2.0, w=0.0)
3.000000: BED(nfs=1.0, w=0.0)
4.000000: BED(nfs=0.0, w=0.0)
5.000000: BED(nfs=-1.0, w=0.0)
6.000000: BUZZ
6.000000: << Day time = 6.0; slept_hour_n = 6.0; >>
6.000000: HOME(nfs=0.0, w=0.0)
7.000000: BUZZ
7.000000: << 7'oclock: slept_hour_n = 6.0; >>
7.000000: WORK(nfs=0.5, w=0.0)
8.000000: WORK(nfs=1.5, w=1.0)
...


With the current rule set no errors appear. Adding the constraint that at work the need for sleep shall not be greater than 9, i.e.:

on WORK:
WORK.nfs < 9;


results in a broken rules which is then reported in the trace:

...
35.000000: WORK(nfs=6.0, w=4.0)
36.000000: WORK(nfs=7.0, w=5.0)
36.000000: << Day time = 12.0; slept_hour_n = 0.0; >>
37.000000: WORK(nfs=8.0, w=6.0)
38.000000: WORK(nfs=9.0, w=7.0)
dude.tlr:14: rule broken.
OUT/test.pl.txt:44: at this point.
...


HWUT reports the location of the broken rule in a ‘gcc’ compiler output format, so that editors can jump onto it by a click and/or a push of return. Further, it documents that the error occured at line 44 of the list of events.