@b3m2a1 thanks for the link. But to tell you the truth, without an easy to use debugger in Mathematica, all the above means little to me. I think one of the main reasons no body uses Mathematica to develop large applications with it, is that it has no debugger. Not even command line one (like gdb). Imagine you have 100,000 lines Mathematica application and have to find where a bug is, and have no access to a debugger. Good luck doing that.

I mean I've developed 10k+ loc Mathematica packages in the past and that's never been an issue for me, but I also don't even bother to use a debugger when I use other IDEs. I've always been partial to print + exception raising to isolate issues since debuggers tend to add more overhead and complexity than they're worth in my experience

@b3m2a1 using debugger does not mean print debugging is not useful also. There is a need and time for each. But the majority of developers would say a debugger is very important tool. I know myself when I develop in env. with debugger, I am much more productive as I can find bugs much more easily. I still have tracing done as well. But many times, a debugger can be a life safer and more effective, not only for finding bugs, but just for inspecting things at run time and to examine things.