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How To Create Your Own JVM Language Like Kotlin



The evolution of programming languages has seen the introduction of several languages that run on the Java Virtual Machine (JVM). Kotlin, a modern, expressive language, stands out as a prime example of this innovation. In this article, we delve into the intriguing process of creating your own JVM language, akin to Kotlin. We explore the key steps, tools, and strategies needed to design and implement a language that is not only functional but also user-friendly and powerful.

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Creating a new JVM language involves a deep understanding of the JVM ecosystem, language design principles, and the nuances of existing languages like Java and Kotlin. By following this guide, you’ll gain insights into developing a language that offers unique features, while ensuring seamless integration with the JVM.

The Genesis of a JVM Language

Embarking on the journey of creating a new JVM (Java Virtual Machine) language is both an ambitious and exhilarating venture. This endeavor requires a deep understanding of the JVM ecosystem, thoughtful consideration for language design, and drawing inspiration from existing successful languages such as Kotlin. In this section, we will explore these foundational elements that form the bedrock of developing a JVM language.

Understanding the JVM Ecosystem

The JVM is a pivotal component in the world of Java programming, acting as the execution engine that runs Java bytecodes. It’s crucial to comprehend its architecture, including the class loader, bytecode verifier, JIT compiler, and garbage collector. This understanding ensures that your language can effectively leverage the JVM’s capabilities and maintain compatibility.

Additionally, the JVM ecosystem is not just about Java; it’s a platform for numerous languages like Scala, Groovy, and, of course, Kotlin. Each of these brings unique features and optimizations, showcasing the JVM’s versatility. Familiarizing yourself with how these languages utilize the JVM helps in crafting a language that can stand alongside them.

Key Considerations for Language Design

Language design is an art that balances several factors. Firstly, syntax and semantics are critical. A syntax that is both intuitive and expressive can significantly lower the learning curve, while powerful semantics can enable complex functionalities with simpler constructs.

Another consideration is the type system. Deciding between static and dynamic typing, or perhaps a blend of both, impacts the language’s flexibility and performance. Additionally, memory management, error handling, and concurrency models are aspects that define the language’s characteristics and user experience.

Lastly, interoperability with Java is a factor that can’t be overlooked. A new JVM language should ideally integrate seamlessly with Java, allowing access to the vast array of existing libraries and frameworks in the Java ecosystem.


Syntax forms the surface structure of your language. It’s how the code looks and feels to a developer. When crafting a new JVM language like Kotlin, having an intuitive and expressive syntax is paramount. Let’s illustrate this with an example:

// Kotlin Syntax
fun greet(name: String) {
    println("Hello, $name!")

In this Kotlin code snippet, the syntax is clean and readable. It uses familiar constructs like fun, val, and $name, making it easy for developers to understand and work with.


On the other hand, semantics defines the meaning behind the code. It’s about what the code does and how it behaves when executed. In your language design, powerful semantics can simplify complex tasks. Consider this example:

// Kotlin Semantics
fun calculateSum(numbers: List<Int>): Int {
    var sum = 0
    for (num in numbers) {
        sum += num
    return sum

The semantics of this Kotlin function are clear: it calculates the sum of a list of integers. The language’s semantics allow developers to achieve this functionality using straightforward and concise code.

Balancing syntax and semantics is crucial in creating a language that is both user-friendly and powerful, as demonstrated by Kotlin’s success in the JVM ecosystem.

Inspiration from Existing Languages like Kotlin

Kotlin, a language developed by JetBrains, is an excellent example of a modern JVM language. It offers concise syntax, robust null-safety, and full interoperability with Java. Kotlin’s success lies in its ability to improve upon Java’s verbosity and rigidity, while maintaining familiarity for Java developers.

Studying Kotlin’s approach to common programming challenges, such as handling null values or streamlining data classes, can provide valuable insights. Furthermore, Kotlin’s coroutine support is a testament to how a JVM language can introduce sophisticated features while keeping the syntax user-friendly.

Here’s an example of interoperability between Kotlin and Java:

// Kotlin code
class KotlinClass {
    fun greet() {
        println("Hello from Kotlin!")

// Java code
public class JavaClass {
    public static void main(String[] args) {
        KotlinClass kotlinInstance = new KotlinClass();

In this example, we have a Kotlin class KotlinClass with a method greet(). We then create an instance of KotlinClass in a Java class JavaClass and call the greet() method from Java. This demonstrates how Kotlin and Java can seamlessly work together within the same JVM ecosystem, showcasing the interoperability between the two languages.

The genesis of a JVM language is a complex process that requires a solid grasp of the JVM ecosystem, a thoughtful approach to language design, and learning from the successes and shortcomings of existing languages. By considering these elements, you are laying a strong foundation for a language that not only performs well on the JVM but also resonates with the developer community.

Setting Up Your Development Environment

Creating a new JVM language is a sophisticated task that demands a well-structured development environment. This environment comprises various tools and software crucial for efficient and streamlined development. Moreover, configuring an integrated development environment (IDE) is key to a productive coding experience. Let’s delve into these aspects to set up an optimal environment for JVM language development.

Essential Tools and Software for JVM Language Development

The first step in setting up your development environment is to equip yourself with the essential tools and software. This includes:

Java Development Kit (JDK)

Since you’re developing a language for the JVM, the JDK is indispensable. It includes the Java Runtime Environment (JRE), compilers, and various tools and libraries necessary for Java development. Ensure you have the latest version installed to access the most recent features and optimizations.

Build Tools

Familiarize yourself with build automation tools like Maven or Gradle. These tools are vital for managing project dependencies, automating builds, and streamlining the testing process. They are widely used in the Java ecosystem and offer extensive community support.

Version Control System

A version control system like Git is essential for tracking changes in your language’s codebase, collaborating with other developers, and maintaining a history of your project’s evolution.

Parser Generator

Since you’ll be dealing with language syntax, tools like ANTLR (Another Tool for Language Recognition) or JavaCC (Java Compiler Compiler) are crucial. These tools assist in generating parsers that can interpret the syntax of your new language.

Parser Generator in Action

Imagine you’re designing a new JVM language called “MyLang.” You want MyLang to have a specific syntax for defining functions. Let’s say you want to support function declarations like this:

function add(a: Int, b: Int): Int {
    return a + b;

To parse and understand this syntax, you can leverage a Parser Generator tool like ANTLR or JavaCC.

1. Grammar Definition

You start by defining a formal grammar for your language’s syntax. This grammar describes the structure and rules for valid code in MyLang. Here’s a simplified grammar snippet for the function declaration:

grammar MyLang;

functionDeclaration: 'function' ID '(' parameterList ')' ':' type '{' statement+ '}';

parameterList: parameter (',' parameter)*;

parameter: ID ':' type;

type: 'Int' | 'String' | 'Boolean' | ...;

statement: ...; // Define other language statements here

In this example, you define rules for recognizing a function declaration, parameters, types, and statements in MyLang.

2. Parser Generation

Using your defined grammar, you run the Parser Generator tool (e.g., ANTLR) on your grammar file. The tool generates a parser code in your chosen programming language (e.g., Java, Kotlin).

3. Integration with Compiler

You integrate the generated parser into your language’s compiler. When the compiler processes MyLang code, it uses the parser to break down the code into a structured format that the compiler can work with.

4. Syntax Validation

As developers write MyLang code, they can now use your language’s syntax, including the function declaration syntax shown earlier. When they compile or run their MyLang programs, the parser ensures that the code adheres to the defined syntax rules. If there are syntax errors, the parser can provide informative error messages to help developers correct their code.

By incorporating a Parser Generator tool like ANTLR or JavaCC into your language development workflow, you streamline the process of parsing and interpreting the syntax of your new JVM language, making it easier for developers to write correct code in MyLang.

JVM Profiler

Tools like VisualVM or JProfiler help in monitoring the performance of your language on the JVM. They provide insights into memory usage, CPU load, and other vital metrics that are crucial for optimizing your language’s performance.

Configuring an Integrated Development Environment (IDE)

Choosing and configuring an IDE is a personal choice but significantly impacts productivity. IDEs like IntelliJ IDEA, Eclipse, or Visual Studio Code are popular in the JVM ecosystem. Here are some tips for configuring your IDE:

Setting up a development environment for creating a JVM language involves selecting and configuring the right set of tools and software. This environment is a blend of the Java ecosystem staples and specialized tools for language development. With a properly configured IDE, the process of developing, testing, and debugging your language becomes much more efficient and enjoyable.

Language Design Principles

Designing a new programming language for the JVM is a nuanced and challenging task. It requires a careful balance between creating a syntax that is easy to understand and providing powerful semantics that meet modern programming needs. In this section, we explore the key principles of language design, focusing on how to balance simplicity and power in syntax and semantics, and the importance of incorporating features that cater to contemporary programming requirements.

Syntax and Semantics: Balancing Simplicity and Power

The syntax of a language is its structure or form, while semantics refer to the meaning of the constructs. Achieving a balance between these two is crucial for the success of a new language:

Incorporating Features for Modern Programming Needs

Modern programming has evolved, and new languages need to reflect current and future trends:

The principles of language design for a JVM language involve a delicate balance. The language should be easy enough for beginners to grasp, yet powerful enough for expert developers to perform complex tasks efficiently. Additionally, it should address modern programming challenges and trends, ensuring that it remains relevant and useful in a rapidly evolving tech landscape.

Compiler Construction

The compiler is the heart of any programming language, translating high-level code into machine-readable instructions. In the case of a JVM language, the compiler translates source code into Java bytecode, which can then be executed on the JVM. Understanding the components of a compiler and mastering techniques for efficient bytecode generation are crucial in creating a robust and performant JVM language.

Overview of Compiler Components

A compiler typically consists of several key components, each playing a specific role in the process of translating source code:

  1. Lexer (Lexical Analyzer): This component breaks down the source code into tokens, which are the fundamental building blocks like keywords, operators, identifiers, etc. Lexers strip away comments and whitespace, preparing the raw code for syntactic analysis.

  2. Parser (Syntactic Analyzer): The parser takes tokens from the lexer and forms them into a syntactic structure, often represented as an Abstract Syntax Tree (AST). The AST represents the grammatical structure of the source code, capturing the relationships between different elements in a tree-like form.

  3. Semantic Analyzer: Once the AST is built, the semantic analyzer checks for semantic consistency. This includes verifying type correctness, scope resolution, and other language-specific rules. It ensures that the code not only follows the correct syntax but also makes logical sense.

  4. Intermediate Code Generator: After semantic analysis, the compiler generates an intermediate representation (IR) of the code. This IR is a lower-level representation of the program, which is independent of the machine language but easier to translate into bytecode.

  5. Optimizer: The optimizer improves the intermediate code for performance enhancements. This may involve removing redundant code, optimizing loops, and other techniques to make the bytecode run more efficiently.

  6. Code Generator: The final step is to translate the optimized IR into Java bytecode. This bytecode is what gets executed on the JVM. The code generator must ensure that this bytecode adheres to the JVM specifications for compatibility and performance.

Techniques for Efficient Bytecode Generation

Efficient bytecode generation is essential for the performance of your language on the JVM. Some techniques include:

Constructing a compiler for a new JVM language is a complex but rewarding challenge. It involves building a series of components that together translate high-level code into Java bytecode. By employing efficient techniques in bytecode generation, you can ensure that your language not only runs correctly on the JVM but also does so with optimal performance.

Integrating with the JVM

Integrating a new programming language with the Java Virtual Machine (JVM) is a critical step in its development. This integration ensures that the language can leverage the JVM’s robust architecture and vast ecosystem. Achieving compatibility with JVM standards and effectively utilizing its libraries and frameworks are key aspects of this process. Let’s explore how to effectively integrate a new JVM language.

Ensuring Compatibility with JVM Standards

To ensure that your language works seamlessly with the JVM, adherence to JVM standards is essential:

  1. Bytecode Compliance: The Java bytecode is the instruction set of the JVM. Your compiler should generate bytecode that aligns with the JVM’s specifications. This ensures that the JVM can correctly execute the code produced by your language.

  2. Java Memory Model (JMM) Compliance: The JMM defines how threads interact through memory in Java. Understanding and adhering to this model is crucial for ensuring that multi-threaded applications written in your language behave predictably on the JVM.

  3. Garbage Collection: The JVM has a sophisticated garbage collection mechanism. Designing your language to work well with this mechanism, perhaps by encouraging immutable data structures or effective resource management patterns, can lead to better performance and reliability.

  4. Performance Considerations: The JVM includes Just-In-Time (JIT) compilation and other optimization techniques. Ensuring that your language’s features and idioms are amenable to these optimizations can greatly enhance performance.

Leveraging JVM Libraries and Frameworks

One of the major advantages of creating a JVM language is access to a rich ecosystem of libraries and frameworks:

  1. Java Standard Library: Your language should be able to interact seamlessly with the Java Standard Library. This allows developers using your language to leverage a wide array of functionalities available in Java.

  2. Third-Party Libraries: Java has a vast array of third-party libraries for everything from web development to data science. Ensure that your language can utilize these libraries without cumbersome bridging code or performance penalties.

  3. Frameworks and Tools Integration: Integration with popular Java frameworks and development tools (like Spring, Hibernate, or Maven/Gradle) is essential. This integration not only enriches the development experience but also encourages adoption by allowing your language to fit into existing Java-centric workflows and ecosystems.

  4. Interoperability with Other JVM Languages: Consider how your language will interoperate with other JVM languages like Kotlin, Scala, or Groovy. Smooth interoperability can make your language a more attractive choice for projects already using these languages.

Integrating with the JVM is a multifaceted process that requires a deep understanding of JVM standards and an ability to leverage its extensive library ecosystem. By ensuring compatibility and effective utilization of the JVM’s features, your language can achieve high performance, reliability, and a broad appeal to the Java developer community.

Testing and Debugging Strategies

Effective testing and debugging strategies are crucial for the development of a new JVM language. These strategies ensure the reliability and stability of the language, making it a trustworthy tool for developers. In this section, we will cover the essentials of building a robust testing framework for your language and delve into debugging techniques that are specific to JVM languages.

Building a Robust Testing Framework for Your Language

A comprehensive testing framework is pivotal for validating the functionality and performance of your language. Here’s how you can build one:

  1. Unit Testing: Start with unit tests for individual components of your language, such as the lexer, parser, and compiler. This helps in catching and isolating bugs early in the development process.

  2. Integration Testing: Once unit testing is in place, move on to integration tests. These tests should cover how different parts of your language work together, such as syntax parsing and bytecode generation.

  3. End-to-End Testing: Implement end-to-end tests to simulate real-world scenarios. These tests should cover the entire process from writing code in your language to its execution on the JVM.

  4. Performance Testing: Since your language runs on the JVM, performance testing is crucial. This includes testing for memory usage, CPU efficiency, and speed of execution.

  5. Regression Testing: As your language evolves, regression tests ensure that new changes don’t break existing functionalities. Automated regression tests can be particularly beneficial.

  6. Community-Based Testing: Once your language reaches a certain level of maturity, open it up for community testing. Feedback from real-world users can be invaluable in identifying issues and areas for improvement.

Debugging Techniques Specific to JVM Languages

Debugging a JVM language can be challenging but understanding the JVM’s workings can greatly aid the process:

  1. JVM Debugging Tools: Familiarize yourself with JVM debugging tools like VisualVM or the Java Debugger (JDB). These tools can help you monitor runtime behavior and pinpoint issues.

  2. Logging and Monitoring: Implement comprehensive logging within your language’s runtime. This can provide insights into how your language interacts with the JVM, especially in the case of performance issues or crashes.

  3. IDE Integration: If possible, integrate debugging support into an IDE. This provides a more intuitive interface for developers to debug code written in your language.

  4. Bytecode Analysis: Sometimes, the issue may lie in the generated bytecode. Tools like ASM or Javap can be used to inspect and analyze the generated bytecode for inconsistencies or errors.

  5. Test Cases as Debugging Tools: Encourage the use of comprehensive test cases by developers. Well-designed test cases can help in quickly identifying the source of a bug.

  6. Handling JVM-Specific Exceptions: Equip your language with mechanisms to handle and report JVM-specific exceptions in a way that’s understandable to the user.

Building a robust testing framework and employing effective debugging strategies are key to the development of a stable and reliable JVM language. These practices not only help in maintaining the quality of your language but also in building trust within the developer community.

Community Engagement and Documentation

The success of a new JVM language is not solely dependent on its technical merits; it also hinges significantly on community engagement and comprehensive documentation. Building a vibrant community and providing thorough documentation are essential strategies for encouraging adoption and fostering the growth of your language. In this section, we will discuss how to effectively engage with the community and the critical role of documentation in the adoption of your language.

Fostering a Community for Your Language

Creating a strong community around your JVM language can drive its growth and development:

  1. Open Source Development: Consider making your language open source. This approach can encourage contributions from developers worldwide and foster a sense of ownership and investment in the language’s future.

  2. Online Platforms: Utilize platforms like GitHub, Stack Overflow, or specific forums for your language. These platforms can serve as venues for discussion, problem-solving, and sharing of ideas.

  3. Regular Updates and Engagement: Keep the community informed about developments, updates, and future plans. Regular blog posts, newsletters, or webinars can be effective.

  4. Contributor Recognition: Recognize and appreciate contributions from community members, whether it’s through code contributions, documentation, or helping others. This can motivate ongoing engagement.

  5. Meetups and Conferences: Organizing or participating in meetups, conferences, and hackathons can increase visibility and attract new users and contributors.

  6. Feedback Mechanisms: Implement channels for users to provide feedback and suggestions. This could be through surveys, issue trackers, or discussion forums.

Importance of Comprehensive Documentation in Language Adoption

Well-crafted documentation is vital for the adoption and effective use of your language:

  1. Getting Started Guides: Provide clear, concise, and easy-to-follow guides for beginners. These should include installation instructions, setup procedures, and a simple “Hello, World!” program.

  2. API Documentation: Ensure that all features, libraries, and APIs of your language are thoroughly documented. This documentation should be easily accessible and searchable.

  3. Tutorials and Examples: Offer a range of tutorials and example projects. These resources are invaluable for new users trying to understand the language’s capabilities and best practices.

  4. Best Practices and Style Guidelines: Provide guidelines on best practices and coding styles. This helps in maintaining consistency and quality in code written by the community.

  5. Language Specification: For those interested in the deeper aspects of your language, provide a detailed language specification. This can include syntax definitions, semantic behavior, and compilation details.

  6. Multimedia Resources: Consider offering video tutorials, webinars, or interactive learning resources. These can be especially helpful for visual or hands-on learners.

Fostering a robust community and providing comprehensive documentation are crucial elements in the success of a new JVM language. Engaging with the community helps in building a supportive and collaborative ecosystem, while thorough documentation ensures that users can effectively learn and utilize the language. These elements combined can significantly enhance the adoption and long-term viability of your language.

The Road Ahead: Iteration and Improvement

The development of a JVM language is an ongoing process, requiring continuous iteration and improvement. As technology evolves and user needs change, so must your language. This dynamic process involves regularly refining your language and staying ahead of emerging programming trends. In this section, we’ll explore strategies for evolving your language and aligning it with the ever-changing landscape of programming.

Strategies for Evolving and Refining Your Language

Evolving and refining a programming language is a delicate balance of innovation, user feedback, and technological advancements:

  1. Incorporate User Feedback: Actively seek and incorporate feedback from your language’s user community. This feedback can provide invaluable insights into the language’s usability, performance issues, and desired features.

  2. Regular Updates and Releases: Establish a schedule for regular updates and new releases. This helps in steadily improving the language and keeping the user base engaged with new features and enhancements.

  3. Backward Compatibility: While evolving your language, consider the impact of changes on existing codebases. Strive to maintain backward compatibility to avoid alienating current users.

  4. Performance Optimization: Continuously work on optimizing the performance of your language. This includes improving the efficiency of the compiler, runtime, and the standard library.

  5. Scalability and Security: Regularly update your language to enhance scalability and security. These aspects are crucial for enterprise-level applications and modern software development.

To ensure the relevance and competitiveness of your language, staying abreast of programming trends and user needs is essential:

  1. Follow Technology Trends: Keep an eye on emerging trends in the software industry, such as artificial intelligence, cloud computing, and IoT. Consider how your language can support these technologies.

  2. Community Engagement: Stay engaged with the programming community at large. Participating in forums, conferences, and workshops can provide insights into what developers are looking for in a language.

  3. Adapt to New Paradigms: Be open to adopting new programming paradigms and concepts. For example, if functional programming gains more traction, consider enhancing your language’s functional programming capabilities.

  4. Collaborate with Academia and Industry: Collaborations with academic institutions and industry can drive innovation in your language. These collaborations can also provide early insights into emerging technologies and methodologies.

  5. Cross-Platform Capabilities: Ensure that your language evolves to support cross-platform capabilities. This is increasingly important in a world where applications are expected to run on multiple devices and platforms.

In summary, the road ahead for a JVM language involves constant iteration and improvement, guided by user feedback, technological advancements, and emerging programming trends. Staying responsive to these factors will help your language remain relevant, effective, and popular among its user base. By continually evolving and refining your language, you can ensure its longevity and significance in the programming world.

By following this guide, you’ll be well on your way to creating a JVM language that stands out in the ever-growing world of programming languages, potentially following in the footsteps of successful languages like Kotlin.