Sources

The project can be cloned from github repository.
The revision described in this post is 50e6996a4faf8d5b469d291a029be05f9e6c9520.

Parser rules changes

In previous post I mentioned few things I would like to add to the language. The first one is going to be obviously a class scope.

Modification made to the language parsing rules:

compilationUnit : ( variable | print )* EOF;
variable : VARIABLE ID EQUALS value;

has been changed to:

compilationUnit : classDeclaration EOF ; //root rule - our code consist consist only of variables and prints (see definition below)
classDeclaration : className '{' classBody '}' ;
className : ID ;
classBody :  ( variable | print )* ;
  • The file must consist of one and only one classDeclaration.
  • class declaration consist of className followed by body inside curly brackets
  • the body is the same thing as it used to be in prototype - variable declaration or prints

This is how the parse tree looks after modifications (You can live preview parse tree using intellij plugin - https://www.youtube.com/watch?v=h60VapD1rOo):

Parse Tree

Compiler changes

Most of the changes involve moving top-level code from ByteCodeGenerator class to CompilationUnit and ClassDeclaration. The logic is as follows:

  1. Compiler grabs parse tree values from SyntaxParseTreeTraverser:
  2. Compiler instantiates CompilationUnit:

    //Compiler.java
    final CompilationUnit compilationUnit = new SyntaxTreeTraverser().getCompilationUnit(fileAbsolutePath);
    //Check getCompilationUnit() method body on github
    
  3. CompilationUnit instantiates ClassDeclaration (passes class name, and instructions list)
  4. ClassDeclaration executes class specific instructions and loops over ClassScopeInstructions:

     //ClassDeclaration.java
     MethodVisitor mv = classWriter.visitMethod(ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
     instructions.forEach(classScopeInstruction -> classScopeInstruction.apply(mv));
    

Parse Tree

One additional thing that changes is that the output .class file will have name based on the class declaration regardless of input *.enk filename:

String className = compilationUnit.getClassName();
String fileName = className + ".class";
OutputStream os = new FileOutputStream(fileName);
IOUtils.write(byteCode,os);

Jakub Dziworski

JVM Dev Blog