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https://github.com/sviperll/adt4j

adt4j - Algebraic Data Types for Java
https://github.com/sviperll/adt4j

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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](http://en.wikipedia.org/wiki/Algebraic_data_type) 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:



```java

// 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) {

    super(base);

  }



  // Example of "pattern-matching"

  int eval() {

    return accept(new ExpressionVisitor() {

      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)

  @Visitor(resultVariableName="R")

  interface ExpressionVisitor {

    @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);

  }



}

```



Features

--------



 * 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

------------



 * maven-compiler-plugin version 3.2 and later doesn't work nicely with

   annotation processors, see [MCOMPILER-235](https://issues.apache.org/jira/browse/MCOMPILER-235).

   Only clean builds work. Repeated compilation causes duplicate class errors.



 * It is possible to support explicit recursive data-types definitions

   without `selfReferenceVariableName` hack, but

   [javac bug](http://mail.openjdk.java.net/pipermail/compiler-dev/2015-November/009864.html)

   prevents it from working. It works when no type-parameters are used,

   see [IntListVisitor.java example](https://github.com/sviperll/adt4j/blob/master/adt4j-examples/src/main/java/com/github/sviperll/adt4j/examples/IntListVisitor.java.



License

-------



ADT4J is under BSD 3-clause license.



Flattr

------



[![Flattr this git repo](http://api.flattr.com/button/flattr-badge-large.png)](https://flattr.com/submit/auto?user_id=sviperll&url=https%3A%2F%2Fgithub.com%2Fsviperll%2Fadt4j&title=adt4j&language=Java&tags=github&category=software)



Installation

------------



Use maven dependency to use ADT4J:



```xml



  com.github.sviperll

  adt4j

  3.2



```



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.



```xml



  com.github.sviperll

  adt4j-shaded

  3.2



```



Changelog

---------



See [NEWS file](https://github.com/sviperll/adt4j/blob/master/NEWS.md).



Usage

-----



See [Tutorial](https://github.com/sviperll/adt4j/wiki/Tutorial)



Build

-----



    $ git clone [email protected]:sviperll/adt4j.git

    $ cd adt4j

    $ mvn test



Check for errors and warnings.



ADT4J is built to be compatible with Java 7.

See [universal-maven-parent](https://github.com/sviperll/universal-maven-parent) project's documentation

for instructions about building projects compatible with JDK7.