Introduction to SimpleLanguage

To implement your own language, get started by extending an existing language such as SimpleLanguage. SimpleLanguage is a demonstration language built using the Language API. The SimpleLanguage project provides a showcase on how to use the Language APIs for writing your own language. It aims to use most of the available Truffle language implementation framework (henceforth “Truffle”) features, and documents their use extensively with inline source documentation.

The SimpleLanguage demonstration language is licensed under the Universal Permissive License (UPL).

Prerequisites #

  • Maven available in your system.
  • GraalVM installed.
  • The mx tool for the development of GraalVM projects (see below).

Get Started #

  1. Clone the SimpleLanguage repository by running:
     git clone
  2. Execute mvn package from the SimpleLanguage directory to build the language. Before that, verify that native-image is available with your GraalVM installation to avoid a build failure:
     cd simplelanguage
     native-image --version
     mvn package

    The command builds the slnative executable in the simplelanguage/native directory and the sl-component.jar language component.

    You can disable the SimpleLanguage native executable build during the packaging phase by running:

     export SL_BUILD_NATIVE=false
     mvn package
  3. Run SimpleLanguage from the project root directory:
     ./sl language/tests/
  4. To see assembly code for the compiled functions, run:
     ./sl -disassemble language/tests/

IDE Setup #

The Truffle framework provides language-agnostic infrastructure to realize standard IDE features by providing additional APIs. If you would like to experiment with your language and get the benefits of an IDE, consider importing SimpleLanguage as an example.

Eclipse #

The SimpleLanguage teaching project has been tested with Eclipse Neon.2 Release 4.6.2, and Eclipse Oxygen.3A. To import the project directory to the desirable Eclipse environment:

  1. Open Eclipse with a new workspace.
  2. Install the m2e and m2e-apt plugins from the Eclipse marketplace (Help -> Eclipse Marketplace).
  3. Finally, import the SimpleLanguage project from File -> Import -> Maven -> Existing Maven Projects -> browse to the SimpleLanguage directory -> Finish.

NetBeans #

NetBeans provides GUI support for debugging arbitrary languages. To upload SimpleLanguage to NetBeans interface, go to File -> Open Project -> select simplelanguage directory -> check Open Required Projects -> open Project.

IntelliJ IDEA #

The SimpleLanguage project was tested with IntelliJ IDEA. Open IntelliJ IDEA and, from the main menu bar, select File -> Open -> Navigate to and select the simplelanguage directory -> Press OK. All dependencies will be included automatically.

Dump Graphs #

To investigate performance issues, consider using the Ideal Graph Visualizer (IGV) on top of GraalVM. IGV is developed to view and inspect intermediate representation graphs – a language-independent intermediate representation (IR) between the source language and the machine code, generated by the compiler. IGV is free to use.

  1. Set up the mx tool on your computer.
    • Clone the mx repository by running:
       git clone
    • Clone the Graal repository to your work directory:
       git clone
    • Add mx to the PATH environment variable:
       export PATH="/path/to/mx:$PATH"
    • To check whether the installation was successful, run the command:
       mx --version 
  2. Launch IGV with mx:
     mx -p graal/compiler igv
  3. Execute the following from the SimpleLanguage root directory to dump graphs to IGV:
     ./sl -dump language/tests/

This dumps compiler graphs in the IGV format over the network to an IGV process listening on Once the connection is made, you are able to see the graphs in the Outline window. Open a specific graph, search for nodes by name, ID, or by property=value data, and all matching results will be shown. Learn more here.

Debug #

To start debugging the SimpleLanguage implementation with a Java debugger, pass the -debug option to the command-line launcher of your program:

./sl -debug language/tests/

Then attach a Java remote debugger (such as Eclipse) on port 8000.

SimpleLanguage Component for GraalVM #

Languages implemented with the Truffle framework can be packaged as components which later can be installed into GraalVM using the GraalVM Updater tool. Running mvn package in the SimpleLanguage directory also builds a sl-component.jar. This file is the SimpleLanguage component for GraalVM and can be installed by running:

gu -L install /path/to/sl-component.jar

SimpleLanguage Native Image #

A language built with Truffle can be AOT compiled using Native Image. Running mvn package in the SimpleLanguage directory also builds a slnative executable in the native directory. This executable is the full SimpleLanguage implementation as a single native application, and has no need for GraalVM in order to execute SimpleLanguage code. Besides this, a big advantage of using the native executable when compared to running on GraalVM is the greatly faster startup time as shown bellow:

time ./sl language/tests/
== running on org.graalvm.polyglot.Engine@2db0f6b2
Hello World!

real    0m0.405s
user    0m0.660s
sys     0m0.108s

time ./native/slnative
== running on org.graalvm.polyglot.Engine@7fd046f06898
Hello World!

real    0m0.004s
user    0m0.000s
sys     0m0.000s

This snipped shows a timed execution of a “Hello World” program using the sl launcher script, which runs SimpleLanguage on GraalVM, using Native Image. We can see that when running on GraalVM the execution takes 405ms. Since our SimpleLanguage program does just one print statement, we can conclude that almost all of this time is spent starting up GraalVM and initializing the language itself. When using the native executable we see that the execution takes only 4ms, showing two orders of magnitude faster startup than running on GraalVM.

For more information on the native-image tool consider reading the reference manual.

Disable SimpleLanguage Native Image Build #

Building the native executable through Maven is attached to the Maven package phase. Since the native executable build can take a bit of time, we provide the option to skip this build by setting the SL_BUILD_NATIVE environment variable to false like so:

export SL_BUILD_NATIVE=false
mvn package
[INFO] ------------------------------------------------------------------------
[INFO] Building simplelanguage-graalvm-native
[INFO] ------------------------------------------------------------------------
[INFO] --- exec-maven-plugin:1.6.0:exec (make_native) @ simplelanguage-graalvm-native ---
Skipping the native image build because SL_BUILD_NATIVE is set to false.
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------

Run SimpleLanguage with the Newest (Development) version of the Compiler #

To run SimpleLanguage with the development version of the Graal compiler we must build a GraalVM with that compiler. Clone the graal repository ( and follow the instructions in the vm/ file to build a GraalVM.

Once that’s done, point JAVA_HOME to the newly built GraalVM and proceed with normal building and running of SimpleLanguage.

Run SimpleLanguage Using Command Line #

Executing SimpleLanguage code is normally done with the sl script which sets up the necessary command line depending on whether JAVA_HOME points to GraalVM or another JVM installation. The following subsections describe the command line for both cases.

Run SimpleLanguage with GraalVM as JAVA_HOME #

Assuming JAVA_HOME points to the GraalVM installation and that the current working directory is the simplelanguage directory, to run SimpleLanguage one should execute the following command:

$JAVA_HOME/bin/java \
    -cp launcher/target/launcher-22.1.0-SNAPSHOT.jar \
    -Dtruffle.class.path.append=language/target/simplelanguage.jar \ language/tests/

In short, we place the launcher JAR file on the class path and execute its main class, but we inform GraalVM of the presence of SimpleLanguage by using the -Dtruffle.class.path.append option and providing it the path to the fat language JAR file. Having the language on a separate class path ensures a strong separation between the language implementation and its embedding context (in this case, the launcher).

Disable Class Path Separation

NOTE! This should only be used during development.

For development purposes it is useful to disable the class path separation and enable having the language implementation on the application class path (for example, for testing the internals of the language).

The Language API JAR file on Maven Central exports all API packages in its module-info. Apply the --upgrade-module-path option together with -Dgraalvm.locatorDisabled=true and this JAR file to export Language API packages:

-Dgraalvm.locatorDisabled=true --module-path=<yourModulePath>:${truffle.dir} --upgrade-module-path=${truffle.dir}/truffle-api.jar

A sample POM using --upgrade-module-path to export Language API packages can be found in the Simple Language POM.xml file.

Note: Disabling the locator effectively removes all installed languages from the module path as the locator also creates the class loader for the languages. To still use the builtin languages add them to the module-path by pointing the module-path to all needed language homes (for example, $GRAALVM/languages/js).

Other JVM Implementations #

Unlike GraalVM, which includes all the dependencies needed to run a language implemented with Truffle, other JVM implementations need additional JAR files to be present on the class path. These are the Language API and GraalVM SDK JAR files available from Maven Central.

Assuming JAVA_HOME points to a stock JDK installation, and that the current working directory is the simplelanguage directory and the Language API and GraalVM SDK JAR files are present in that directory, one can execute SimpleLanguage with the following command:

$JAVA_HOME/bin/java \
    -cp graal-sdk-22.1.0.jar:truffle-api-22.1.0.jar:launcher/target/launcher-22.1.0-SNAPSHOT.jar:language/target/simplelanguage.jar \ language/tests/

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