Here are some debugging techniques

• Reduce the specification and the input to localize the error

• Print intermediate results using debug

• Write a unit test using StrategoUnit^?

• Use a FormatChecker to verify the results of transformations

• Compare your code with the list of ThingsThatCannotWork^?

• Use the debug strategy with an argument. It turns out that the debug strategy will accept a string prefaced by an exclamation mark, thus: debug(!"after doing something or other: ") If you do this, it will print the current aterm as usual, but first it will print the string, so that you know where in the program it is.