Here are some tips on how to debug what is happening on the transition from groovy source code into the generated bytecode.
For these examples let's assume the file 'Hello.groovy' contains
GroovyLexer (viewing Antlr Tokens)
To view the antlr tokens that the source code has been broken into you need to do the following in groovy-core subdirectory
GroovyRecognizer (viewing Antlr AST)
To view the antlr AST that the recognized tokens have built
AntlrParserPlugin (viewing Groovy AST)
To view the Groovy AST that is one step closer to the generated bytecode
One interesting bytecode viewer is jclasslib which renders Hello.class in this manner...