div

[oja...@gmail.com]

I was looking in the language definition and saw that 'div' was a keyword. I'm pretty sure its some kind of relational operator, but is there any documentation of what it means or how to use it?

[Maarten Gmail]

Ojaneeo,

Div is the “div” operator, with a definition of the modulus, remainder, or integer division, operator:

http://www.irietools.com/iriepascal/progref319.html

http://mathbits.com/MathBits/Java/DataBasics/Mathoperators.htm

Maarten.

On Dec 1, 2015, at 4:35 PM, oja...@gmail.com wrote:

I was looking in the language definition and saw that 'div' was a keyword. I'm pretty sure its some kind of relational operator, but is there any documentation of what it means or how to use it?

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[oja...@gmail.com]

Thanks, Maarten.

Using it as an operator for a precondition, the Brahms compiler seems to want <operand> div <operand> is <truth value>

Do you know why this might be the case? 

When I try to use integers as the operands, it gives me the message:

Illegal type on left hand side in relational comparison 'int'

Am I missing something?

Jane

[Maarten Sierhuis]

Jane,

Yes, I guess you are missing something. "div" is NOT a precondition evaluation-operator, if that's how you are using it. It is a term part of an expression. An expression can be a left-hand or right-hand-side of a precondition with an evaluation-operator in the middle.

Study the BNF for a precondition:

http://ejenta.com/documentation#precondition

Can you provide an example of what you're trying to do?

Maarten.

[oja...@gmail.com]

Definitely! I'm just trying to get familiar with the language, so my example is pretty trivial:

agent DivTest {

attributes:

int x;

int y;

initial_beliefs:

(current.x = 10);

(current.y = 4);

activities:

primitive_activity wait()

{

max_duration: 10;

}

java println(string message) { 

class: "brahms.base.system.PrintlnActivity"; 

}

java printBelief(Concept aboutConcept, string aboutAttribute, string aboutAttributeType) {

class: "brahms.base.system.PrintBeliefActivity";

}

workframes:

workframe wf_divTest

{

repeat: true;

when (

knownval(current.x div current.y  = 2)  //With this, the compiler doesn't like '=', and wants 'is' instead

                                        //If I change it to 'is' then it wants '2' to be 'unknown' 'true' or 'false'

                                        //If I change the '2' to one of those values, it tells me "Illegal type on left hand side in relational comparison 'int'

                                        //which is why I thought 'div' was a relational operator initially

)

do {

wait();

println("BEFORE:   ");

printBelief(current, "x", "attribute");

printBelief(current, "y", "attribute");

conclude((current.x = current.x + 1));

conclude((current.y = current.y + 1));

println("AFTER:     ");

printBelief(current, "x", "attribute");

printBelief(current, "y", "attribute");

[Maarten Sierhuis]

Hi Jane,

I did a quick test, and it seems indeed that the compiler has trouble with the div operator in preconditions. I never use any of Brahms’ math operators in preconditions, since dealing with assignments and evaluations in a precondition is problematic. You can do things easily in the body of a workframe. Here is a simple solution (I use an integer division):

/**
* @author sierhuis
* @version $Revision:$ $Date:$ $Author:$
*/
agent DivTest memberof SystemGroup {

attributes:
int x;
int y;

int z;

initial_beliefs:
(current.x = 10);
(current.y = 4);

(current.z = 2);

workframes:
workframe wf_divTest
{
repeat: true;

when ((current.z = 2))
do {
println("BEFORE: ");
printBelief(current, "z", "attribute");

printBelief(current, "x", "attribute");
printBelief(current, "y", "attribute");
conclude((current.x = current.x + 1));
conclude((current.y = current.y + 1));

conclude((current.z = current.x / current.y));

println("AFTER: ");
printBelief(current, "x", "attribute");
printBelief(current, "y", "attribute");

printBelief(current, "z", "attribute");
}
}
}


Here is another solution (without z as a belief) :

/**
* @author sierhuis
* @version $Revision:$ $Date:$ $Author:$
*/
agent DivTest memberof SystemGroup {

attributes:
int x;
int y;

initial_beliefs:
(current.x = 10);
(current.y = 4);

workframes:
workframe wf_divTest
{
repeat: true;

variables:
forone(int) x;
forone(int) y;
forone(int) z;
when ((x = current.x) and
(y = current.y) and
(z = x / y) and
(z = 2))
do {

println("BEFORE: ");
printBelief(current, "x", "attribute");
printBelief(current, "y", "attribute”);

println_n(“z = %1”, z);

conclude((current.x = current.x + 1));
conclude((current.y = current.y + 1));
println("AFTER: ");
printBelief(current, "x", "attribute");
printBelief(current, "y", "attribute");

println_n(“z = %1”, z);
}
}
}

Maarten Sierhuis, Ph.D.
Founder & CTO, Ejenta

[oja...@gmail.com]

Thanks for the solution, Maarten!