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Authoring Languages for LionWeb

LionWeb is an open initiative to enable interoperability among language engineering tools.

Therefore, typically one would:

  • Use one of the tools compatible with LionWeb to author a language
  • Export the language into LionWeb format and import it in other tools

Alternatively, a language can also be defined programmatically using the API provided by LionWeb Java.

Using LionWeb-compatible tools to author languages​

In most real-world use cases, language definitions (or metamodels) are created using dedicated language workbenches or modeling tools. These tools provide expressive, user-friendly environments to author, maintain, and evolve languages.

You may want to consider

  • JetBrains MPS: A powerful projectional editor with LionWeb export support provided through LionWeb MPS.
  • Freon: A lightweight web-based projectional editor, with support for LionWeb provided through LionWeb-Freon-M3.
  • Starlasu: A cross-platform framework for language engineering framework developed by Strumenta.

These tools allow engineers to create languages using their built-in mechanisms and then export them to LionWeb-compatible formats. Once exported, these languages can be:

  • Used in other LionWeb-aware tools.
  • Serialized to formats like JSON and Protobuf
  • Re-imported across the ecosystem.

This workflow maximizes interoperability and reuse, allowing language definitions to move seamlessly across platforms.

Authoring Languages Programmatically​

While most users rely on external tools, it is also possible to author languages programmatically using LionWeb-Java.

Using the API in the core module, you can define metamodels directly in Java code. This gives you the flexibility to:

  • Build metamodels dynamically.
  • Serialize and persist them.
  • Use them in JVM-Based libraries and programs.
  • Export them to LionWeb formats for use elsewhere.

Supported Serialization Formats​

The LionWeb Java implementation supports serialization in:

  • JSON (standard and human-readable)
  • ProtoBuf (compact binary format)

Example: Defining a Language Programmatically​

The following example shows how to define a minimal language with a single concept Task that has a name property.

package com.example;

import io.lionweb.lioncore.java.language.Concept;
import io.lionweb.lioncore.java.language.Language;
import io.lionweb.lioncore.java.language.LionCoreBuiltins;
import io.lionweb.lioncore.java.language.Property;
import io.lionweb.lioncore.java.serialization.JsonSerialization;
import io.lionweb.lioncore.java.serialization.SerializationProvider;
import io.lionweb.lioncore.java.utils.LanguageValidator;

import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;

public class LanguageAuthoringExample {
    public static void main(String[] args) throws Exception {
        // Define the 'Task' concept
        Concept taskConcept = new Concept("Task");
        taskConcept.setID("Task-id");
        taskConcept.setName("Task");
        taskConcept.setKey("Task");
        taskConcept.setAbstract(false);

        // Add a 'name' property
        Property nameProperty = new Property();
        nameProperty.setID("task-name-id");
        nameProperty.setName("name");
        nameProperty.setKey("task-name");
        nameProperty.setType(LionCoreBuiltins.getString());
        taskConcept.addFeature(nameProperty);

        // Define the language container
        Language taskLanguage = new Language();
        taskLanguage.setID("task-id");
        taskLanguage.setKey("task");
        taskLanguage.setName("Task Language");
        taskLanguage.setVersion("1.0");
        taskLanguage.addElement(taskConcept);

        LanguageValidator.ensureIsValid(taskLanguage);

        // Serialize to JSON
        JsonSerialization serialization = SerializationProvider.getStandardJsonSerialization();
        String json = serialization.serializeTreesToJsonString(taskLanguage);
        Files.write(Paths.get("task-language.json"), json.getBytes(StandardCharsets.UTF_8));
    }
}