Snippets
FAQ for using SARL + SWI Prolog (with JPL) + Maven
This is a collection of questions/issues that arose from my teaching of Agent Oriented Programming, where I have assessments in SARL and SWI Prolog, all packaged with Apache Maven.
If you think a question is worth putting it here, please let me know, I am happy to add it! THANKS!
- FAQ for using SARL + SWI Prolog (with JPL) + Maven
- ECLIPSE
- IntelliJ
- SWI-PROLOG and Java-SWI JPL Connectivity
- MAVEN
- How do I install a JAR dependency manually?
- How do I tell maven to work offline (not check anything on the internet)?
- Why maven is not downloading the sources of dependencies?
- Error from Google Lirary related to a Java 9 class
- How to assemble my whole SARL application in a JAR file?
- I get "no compiler is provided" error, why?
- Maven can throw lots of warnings and xml messages, how do I filter them?
- How can I pass arguments to Maven? For example, variable java.library.path?
- How to configure testing disabled by default?
- SARL
- SARL is similar to Java but has different syntax in many places, how come?
- Seems my SARL application cannot find JPL!
- Can we document SARL code for JAVADOC?
- How do I control the log-level of the Logging built-in capacity?
- How can we know when an agent has been created fully after being spawn?
- Equality and identity comparison (==, ===, !=, !==) in SARL and checking for null: same as Java ?
- How to return two values? Pairs in SARL
- I cannot pass data to the Initialize of a Behaivor, occurrence.parameters is always empty!
- Cannot access agent owner of a skill in Initialize behavior, why?
- SARL is giving lots of WARNINGS at compile time, how can I avoid them?
- I cannot define a static field in an agent tye declaration (agent, skill, behavior), why?
- Can I make SARL wait in the execution on some thread?
- Emitting events and spawning agents in "on Intialize" behaviors: be careful!
- Strange error in CLI when using occurence on left hand side of assignments
ECLIPSE
We use ECLIPSE to develop SARL applications.
How do I make ECLIPSE know about environment variables (e.g., SARL_VERSION
)?
I can imagine there are other ways, but the way I made it work is by starting ECLIPSE from CLI with the variable exported already:
$ export SARL_ECLIPSE=0.7.2
$ ./eclipse-sarl
If you find another way that ECLIPSE can gather the environment variables (without re-defining them one by one), let me know!
What plugins are useful to develop on SARL in ECLIPSE?
On the SARL ECLIPSE distribution I install:
- The Markdown Text Editor (to edit
README.md
files) - via Marketplace.. - The Prolog Development Tool (ProDT) - via Marketplace.
- This will require first to install Eclipse Dynamic Language Toolkit (DLTK)
- You can use this update link: http://download.eclipse.org/technology/dltk/updates-dev/latest/
- This will require first to install Eclipse Dynamic Language Toolkit (DLTK)
IntelliJ
We use IntelliJ to develop pure Java applications.
When I run an application I get erro saying no jpl in java.library.path
?
IntelliJ cannot find the native library as it does not have LD_LIBRARY_PATH
set correctly. See next question.
How do I tell IntelliJ about environment variables (like LD_LIBRARY_PATH
)?
You set environment variables (if not set already system-wide) for each run/debug configuration.
Since it is painful to do it manually for each, one should first modify the Templates in "Run/Debug Configuration" to include the environment variables needed, for example LD_PRELOAD
, SWI_HOME_DIR
, and LD_LIBRARY_PATH
.
See this post
For example, modify the JUnit template by just enter this string in "Environment variables":
LD_LIBRARY_PATH=/usr/local/swipl-git/lib/swipl/lib/x86_64-linux/;SWI_HOME_DIR=/usr/local/swipl-git/lib/swipl/;LD_PRELOAD=libswipl.so
Then, create a new Run from the template, and it will already inherit the environment variables.
SWI-PROLOG and Java-SWI JPL Connectivity
When using SWI Prolog from Java I recommend checking:
- The JPL documentation maintained by Paul Singleton, which has information on:
- How to access Java from SWI Prolog code: The Prolog API side of JPL
- HOw to access SWI Prolog from Java code: The JAVA API side of JPL
- The types of queries available: One-shot vs Iterative
- How multi-threading queries work under JPL.
Making JPL work under Mac OS
Please refer to this entry in the JPL documentation. (Note: that is from 2018; it may be fixed in newer versions)
What does +
, -
, ?
mean in predicate specifications?
Check here
What environment variables I should care about (in Linux)?
Basically you need to let the system know which SWI Prolog is installed and you want to use.
Linux
If you are using a Linux distribution install, you would do something like this:
export SWI_HOME_DIR=/usr/lib/swi-prolog/
export LD_LIBRARY_PATH=$SWI_HOME_DIR/lib/x86_64-linux/:$SWI_HOME_DIR/lib/amd64/:$LD_LIBRARY_PATH
export LD_PRELOAD=libswipl.so:$LD_PRELOAD # only if necessary and your app complains
The reason why we have two library paths is that lib/amd64/
is used for SWI 7.6.4, whereas lib/x86_64-linux/
is used in 8.x.x versions.
If, instead, you compiled the SWI from git sources and installed at /usr/local/swipl-git
, you would do something like this:
export SWI_HOME_DIR=/usr/local/swipl-git/lib/swipl/
export LD_LIBRARY_PATH=$SWI_HOME_DIR/lib/x86_64-linux/:$SWI_HOME_DIR/lib/amd64/:$LD_LIBRARY_PATH
export LD_PRELOAD=libswipl.so:$LD_PRELOAD # only if necessary and your app complains
Windows
- A system variable
SWI_HOME_DIR
points to the root of SWI install. - System variable
Path
should include%SWI_HOME_DIR%\bin
and%SWI_HOME_DIR%\lib\jpl.jar
.
My Java/SARL application cannot cannot find JPL!
There could be many reasons and it may depend on the OS you are using.
First of all, make sure you have SWI-Prolog installed, either:
- Stable version 7.6.4 as per standard Linux repository or executable install from SWI page.
- Compiled 8.1.x+ version from swipl-devel repo.
- Note current (Feb 2019) stable 8.0.x version has a problem with
libswipl.so
which makes JPL crash.
- Note current (Feb 2019) stable 8.0.x version has a problem with
Second, make sure you also have the JPL package installed in the system. This is an additional SWI module, it is not part of the core.
- In Windows, it is easy as you can click to install JPL Java<-->SWI interface at installation time.
- You should see
jpl.dll
file in%SWI_HOME_DIR%/bin
andjpl.jar
in%SWI_HOME_DIR%/lib
.
- You should see
- In Linux, you need to make sure
libjpl.so
andjpl.jar
are somewhere! If you cannot find it, then you may need to install JPL.- In Ubuntu, it is provided with package
swi-prolog-java
. - In ARCH, you can generate it and install it using AUR package builder and
swi-prolog-git
package. Running the default PKG build file is enough to get JPL installed. - In MAC, we don't know how to make it work, as there is a glitch in one of the packages built for Mac... :-( [if you make it work, please let me know!]
- In Ubuntu, it is provided with package
Finally, make sure your system is aware of both SWI and JPL by setting the appropiate env variables; see previous above.
If you are using SARL, you may also refer to the instructions of the SARL Prolog Capacity
Why do I need to set LD_PRELOAD=libswipl.so
?
To understand the environment library LD_PRELOAD
check this post and this one about library preloading. Also, check this and this posts.
MAVEN
How do I install a JAR dependency manually?
Suppose your application need version 1.2.0.7.2
of artifact sarl-agtcity-mw
from group id org.bitbucket.ssardina-research
, but for some reason it cannot be gathered automatically from the cloud.
Suppose you can get a hold of that dependency and obtain file sarl-agtcity-mw.jar
. How do you install it in the repo? Here it is:
mvn install:install-file -Dfile=sarl-agtcity-mw.jar -DgroupId=org.bitbucket.ssardina-research \
-DartifactId=sarl-agtcity-mw -Dversion=1.2.0.7.2 -Dpackaging=jar
How do I tell maven to work offline (not check anything on the internet)?
Use the -o
option for offline mode (e.g., mvn -o clean package
): https://www.packtpub.com/mapt/book/application_development/9781785286124/8/ch08lvl1sec81/working-in-offline-mode
Note you will still need to build the system online at least one, so that your system has the chance to get all the dependencies and store them under ~/.m2/
Why maven is not downloading the sources of dependencies?
ECLPSE IDE seems to download all sources by default. To get the sources via CLI: mvn dependency:sources
To state the POM to get all sources (and javadocs) of dependencies, check this post
Error from Google Lirary related to a Java 9 class
The version of the maven-compiler-plugin should not be higher than 3.6.2
because the newer versions are using Java 1.9. And, it may cause problems during the compilation process.
In reality, the maven-compiler-plugin is not mandatory at all in the POM because Maven is supposed to download one when needed for compilation. If you encounter strange error related to the use of an Java 9 class from the Google library, then you have to specify the maven-compiler-plugin in order to avoid it:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.2</version>
<configuration>
<source>${compiler.level}</source>
<target>${compiler.level}</target>
<encoding>${project.build.sourceEncoding}</encoding>
</configuration>
</plugin>
How to assemble my whole SARL application in a JAR file?
You can use maven-assembly-plugin
build pluin:
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>BootMAS</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<!-- EXECUTIONS -->
<executions>
<!-- Assemble an application bundle or distribution from an assembly descriptor. -->
<execution>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
Note that with version 3.1.0
this may take quite longer to compile, as all dependencies are packaged into a single, often large, JAR file.
I get "no compiler is provided" error, why?
Make sure you:
- Have JDK installed in your system (the Java development framework that comes with the compiler
javac
), not just the Java runtime environment JRE. - Your
PATH
environemnt variable points to the directory wherejava
andjavac
of the JDK where installed. - Your
JAVA_HOME
points to the directory where the JDK was installed. Alternative, you will need to specify it in yourpom.xm
; see here .
Maven can throw lots of warnings and xml messages, how do I filter them?
To remove the WARNING mesages:
mvn exec:java | grep -v -e WARNING
mvn clean package | grep -v -e WARNING
To also remove all the print out of xml messages (e.g., the ones thrown by the Massim EIS for the Agents in City game):
mvn exec:java | grep -v -e \<.*> -e WARNING -e '^ sent' -e '^ received'
How can I pass arguments to Maven? For example, variable java.library.path
?
You can use the MAVEN_OPTS
environmnt variable that will apply to all calls to Maven. For example:
export MAVEN_OPTS=-Djava.library.path=/usr/local/swipl-git/lib/swipl/lib/x86_64-linux/
How to configure testing disabled by default?
We use the Maven Surefire Plugin with skipping by default:
<properties>
<skipTests>true</skipTests>
</properties>
<!-- JUNIT testing framework -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<!--<scope>test</scope>-->
</dependency>
<build>
<testSourceDirectory>src/java/org/jpl7/test</testSourceDirectory>
...
<plugin>
<!-- Unit test execution -->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.12.4</version>
<configuration>
<!-- Check this: https://maven.apache.org/surefire/maven-surefire-plugin/examples/skipping-tests.html -->
<skipTests>${skipTests}</skipTests>
</configuration>
</plugin>
....
</build>
Then, we can enable the tests via mvn surefire:test -DskipTests=false
SARL
Many of the answers here are almost verbatim explanations from SARL developer Stéphane Galland to my email enquires :-)
SARL is similar to Java but has different syntax in many places, how come?
Because it uses and builts on XTEND framework.
Seems my SARL application cannot find JPL!
There could be many reasons and it may depend on the OS you are using. You need to have SWI-Prolog, JPL package, and the right environment variables set-up.
Check this question
Can we document SARL code for JAVADOC?
Presumably yes:
http://www.sarl.io/docs/official/faq/SyntaxFAQ.html#1-11-can-we-document-sarl-code-for-javadoc
Additionnally, in later version, a sarldoc
command-line tool for helping will be provided.
In 0.8.6 I was not successful. Check this post: https://groups.google.com/forum/#!topic/sarl/E_mhpFWyBFo
How do I control the log-level of the Logging built-in capacity?
See here.
How can we know when an agent has been created fully after being spawn?
An event AgentSpawned
will be emitted when an agent has been created and can be handled, say by a coordinator, to know the agent is now alive! Fo example:
on AgentSpawned {
info("Agent {0} of type {1} has been created successfully and is now alive!",
occurrence.agentIdentifiers, occurrence.agentType)
}
Equality and identity comparison (==
, ===
, !=
, !==
) in SARL and checking for null: same as Java ?
Check here
I believe the mapping is like this because:
- In Xtend the equals operators (
==
,!=
) are bound toObject.equals
. - Java’s identity equals semantic is mapped to the tripple-equals operators
===
and!==
in Xtend.
Check xtend doc here for more details and SARL doc here.
Note directly from SARL developer (Sept 2018): SARL extends a part of Xtend dialect in order to have benefits of several background features, such as the validation tests for type inheritance. Since Xtend and SARL uses Xbase, a large part of the syntax is the same, especially within the blocks of code. (The rest of the syntax is defined in parallel. SARL was inspired by languages such as Scala, Python and Ruby. Several bugs or incoherencies of Xtend are fixed in SARL.
There is still a bit of an issue inside the Xbase library; check this https://github.com/sarl/sarl/issues/852#issuecomment-420842088
I have created an issue regarding null == value: Issue #854.
According to the associated discussion within the Xbase group #300, the error message will be updated to push the developers to use ===
.
How to return two values? Pairs in SARL
Check here
I cannot pass data to the Initialize of a Behaivor, occurrence.parameters is always empty!
Not anymore an issue from 0.9, has been resolved in this issue.
For versions 0.8.6 or less:
From SARL developer in this post](https://groups.google.com/forum/#!topic/sarl/E0TuX-V123U):
Currently, there is no way to set the occurrence.parameters
values with the current API.
The Initialize
event is fired by the registerBehavior
function. As you could see, this function does not provide a mean for passing initialization parameters.
I think the ability to set the Initialize parameters when registering the behaviors is a missed feature from the SARL API.
You could use the following work around:
behavior MyBehavior {
var initParam : Object[]
new (owner : Agent, initParam : Object*) {
super(owner)
this.initParam = initParam
}
on Initialize {
// Do something with this.initParam
}
}
agent MyAgent {
uses Behaviors
on Initialize {
var beh = new MyBehavior(this, "p1")
beh.registerBehavior
}
}
Note that because registration happens after the creation of the behavior module, the initParam
will be available at time of Initialize
execution.
Cannot access agent owner of a skill in Initialize behavior, why?
Summary in this thread
The owner of the skill is set when the skill is attached to the agent. It means that the owner cannot be known within the constructor of the skill. The function install
is invoked just after the skill is installed into the agent.
So:
new {
super()
assert this.owner === null
}
def install {
assert this.owner !== null
}
Importantly, the initialization (via Initialize
event) is not at creation time (constructor) but when the entity is attached to the agent.
Within SARL developers' perspective, constructor statements should be redefined only if you want to set the value of a field that is final (val
keyword), because it is mandatory regarding the semantic of the val keyword.
Consequently, the best practice is that all initializations should be within the on Initialize
. They should avoid constructor definition.
So, the "clean" way to access the agent owner is in the install
method:
skill SWIJPL_KB_Prolog implements KB_Prolog {
var module_name : String
def install {
module_name = this.owner.ID.toString
}
...
}
SARL is giving lots of WARNINGS at compile time, how can I avoid them?
Check here
I cannot define a static field in an agent tye declaration (agent, skill, behavior), why?
Check here
Can I make SARL wait in the execution on some thread?
Yes, use something like TimeUnit.SECONDS.sleep(5)
Emitting events and spawning agents in "on Intialize
" behaviors: be careful!
Check here
More details on how events and spawnning are processed by the SARL execution engine
When the event e
is received by an agent the following algorithm is applied:
if "on Initialize" is currently running then
add e to a buffer of events.
else if "on Destroy" is currently running then
ignore the event.
else
fire(e)
fi
The function fire(e)
retrieves all the "on E
" and runs them in parallel, and there is a synchronization point after the running of all the "on E
" if E
is Initialize
or Destroy
(for forcing synchronous execution of "on Initialize
" and "on Destroy
"). At the end of the "on Initialize
" (after synchronization point), all the buffered events are fired.
Observe that if the event is fired from within the "on Initialize
", the same algorithm is applied whatever the receiving agent.
Regarding spawn()
, the function runs in two parts:
- First, the spawn agent is created. This part is run in the same thread as the caller of spawn, so the spawn call blocks.
- Once the spawn agent has been created, the initialization process runs within a separated thread from the spawner agent. So, the call
spawn()
is now not locked anymore. Then, the created thread runs all the initialization process, including the synchronous execution of "on Initialize
". Consequently, the "on Initialize
" of the spawn agent will not block the spawn caller.
Strange error in CLI when using occurence on left hand side of assignments
From 0.9.0, there is an error if the SARL compiler has detected an assignment to a field of occurrence. Passing a field of occurrence to a function becomes a warning (See FAQ 0.9).
For older versions:
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