How to find line where error occurred in Mathematica notebook?

Question

I have a Mathematica file called myUsefulFunctions.m containing, for example, a function called mySuperUsefulFunction. Suppose I call mySuperUsefulFunction in a notebook and get

Answer 1

Apart from the debugger in the Workbench there's also a debugger built-in in Mathematica. You can find it in the Evaluation menu. It is not well documented and rather difficult/unconventional to get it to work. Here is a step-by-step instruction how to use it:

Assuming you have the debugger switched on in the Evaluation menu your window bar will indicate it's a debug session and you will have a few debugger palettes.

Now select a number of lines you want to act as breakpoints and click on the "break at selection" text. Breakpoints will be marked by a red outline.

and run the code by pressing Shift-return and be prepared for a slight disappointment: it doesn't work. It appears you cannot define breakpoints on the line level. It must be at function level. Also, MMA is rather picky about the functions you can use. The Print function apparently doesn't work neither do assignments. However, the Integrate in this example does, but you have to select its head and both brackets and make that a breakpoint. If you have done that and you then execute the block of code you get this:

The breakpoint is highlighted green, some additional options in the control palette have come available to control further program flow, and there are expressions in the stack window. The rest is more or less similar to a standard debugger. Note that you can nest breakpoints like the Cos in the Integrate. For a language that can have deeply nested structures this is essential.

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Another option would be David Bailey's debugger. He offers the free debugger DebugTrace on his website. I haven't tried it myself but I know David as a very capable Mathematica expert so I trust it must be good.