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Authoring Languages in LionWeb Kotlin

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

While most language definitions are created using high-level tools like MPS, Freon, or StarLasu, LionWeb also supports programmatic language definition — including through the Kotlin API provided by the LionWeb Kotlin libraries.

This approach is useful when:

  • Prototyping or testing language definitions
  • Creating small or generated languages dynamically
  • Using Kotlin-based tooling to generate or manipulate metamodels

Authoring Languages Programmatically in Kotlin​

Using the LionWeb Kotlin API, a language can be constructed through code using a fluent and type-safe DSL built around lwLanguage and related functions.

Below is an example that defines a small language called "Properties", with three concepts:

  • PropertiesPartition (marked as a partition)
  • PropertiesFile
  • Property

It models a structure where a partition contains multiple files, and each file contains multiple properties.

The fluent API take care of the boring details like assigning IDs and keys as needed.

Example: Properties Language in Kotlin​

import io.lionweb.lioncore.java.language.Concept
import io.lionweb.lioncore.java.language.LionCoreBuiltins
import io.lionweb.lioncore.java.serialization.SerializationProvider
import io.lionweb.lioncore.kotlin.Multiplicity
import io.lionweb.lioncore.kotlin.createConcept
import io.lionweb.lioncore.kotlin.createContainment
import io.lionweb.lioncore.kotlin.lwLanguage
import java.io.File

val propertiesPartition: Concept
val propertiesFile: Concept
val property: Concept
val propertiesLanguage =
    lwLanguage("Properties").apply {
        propertiesPartition = createConcept("PropertiesPartition")
        propertiesFile = createConcept("PropertiesFile")
        property = createConcept("Property")

        propertiesPartition.isPartition = true
        propertiesPartition.createContainment("files", propertiesFile, Multiplicity.ZERO_TO_MANY)
        propertiesFile.createContainment("properties", property, Multiplicity.ZERO_TO_MANY)
        property.addImplementedInterface(LionCoreBuiltins.getINamed())
    }

fun main(args: Array<String>) {
    // Save the language to file
    File("properties-language.json").writeText(SerializationProvider.getStandardJsonSerialization().serializeTreesToJsonString(propertiesLanguage))
}

Deriving Languages from Node subclasses​

In LionWeb Kotlin, you can also create Node subclasses and then derive a language from their structure, without having to write it manually. For this, look into the next section.