Comment by rahulmutt

You can use JVM debugging tools and with a guide on how to interpret the results for Eta (or a tool that does the mapping to Eta source code for you), debugging can be pretty awesome. The implementation was specifically designed to re-use the JVM Thread stack as much as possible so that you can get stack traces and figure out the source of the error. You'll get stack traces similar to other JVM languages like Scala and Clojure. See http://eta-lang.org/docs/html/eta-user-guide.html#debugging-... for an example. You can use tools like slf4j-ext as java agents and get nice traces - it's how I debug the Eta runtime.