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adt4j - Algebraic Data Types for Java
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adt4j - Algebraic Data Types for Java

This library implements Algebraic Data Types for Java.
ADT4J provides annotation processor for @GenerateValueClassForVisitor annotation.
ADT4J generates new class for each @GenerateValueClassForVisitor annotation.

It allows you to easily define custom data types. Like this:

// Define Expression data type
@WrapsGeneratedValueClass(visitor = ExpressionVisitor.class)
// ExpressionBase class will be automatically generated by annotation processor
// You can use any other name instead of ExpressionBase, like VeryLongNameThatYouShouldNeverActuallyUse
class Expression extends ExpressionBase {
  public static void main(String[] args) {
    // Static constructor methods are automatically generated for Expression class
    Expression e = mul(sum(lit(5), lit(1)), lit(2));

    // Reasonable default toString implementation is provided:
    System.out.println(e + " = " + e.eval());

  // This is the required boilerplate for wrapper-class
  Expression(ExpressionBase base) {

  // Example of "pattern-matching"
  int eval() {
    return accept(new ExpressionVisitor<Integer>() {
      Integer lit(int i) {
        return i;
      Integer sum(Expression e1, Expression e2) {
        return e1.eval() + e2.eval();
      Integer mul(Expression e1, Expression e2) {
        return e1.eval() * e2.eval();

  // Actual data-type definition
  // Data type is recursive. No special treatment of recursive definition is required.
  @GenerateValueClassForVisitor(wrapperClass = Expression.class)
  interface ExpressionVisitor<R> {
    @GeneratePredicate(name = "isLiteral");
    R lit(int i);

    R sum(@Getter(name = "leftOperand") Expression e1, @Getter(name = "rightOperand") Expression e2);
    R mul(@Getter(name = "leftOperand") Expression e1, @Getter(name = "rightOperand") Expression e2);



  • Support recursive data types
  • Generate hashCode, equals and toString implementations with value semantics
  • Generate predicates, getters and "updaters" with additional annotations
  • Fully customizable API: custom names and access levels for generated methods
  • Optionally generate Comparable implementation with precise compile-time type-check if it is possible
  • Optionally generate serializable classes with precise compile-time type-check if it is possible
  • Sensible error messages
  • Support generated class extention through standard Java's inheritance.
  • Reasonably fast

Known Issues


ADT4J is under BSD 3-clause license.


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Use maven dependency to use ADT4J:


You can use adt4j-shaded artifact to simplify deployment and to avoid dependencies' conflicts. adt4j-shaded has no dependencies and does not pollute classpath. All java-packages provided by adt4j-shaded are rooted at com.github.sviperll.adt4j package.



See NEWS file.


See Tutorial


$ git clone
$ cd adt4j
$ mvn test

Check for errors and warnings.

ADT4J is built to be compatible with Java 7. See universal-maven-parent project's documentation for instructions about building projects compatible with JDK7.

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