Interesting. I've been working on a debugging tool that has some similarities. It's not quite finished yet (still needs the ability to step through execution and toggle breakpoints during runtime), but it's functional enough that I use it in my daily work for browsing through the callstack and variables when an uncaught error occurs. My debugger has a few features I'm pretty happy with, like color-coded file-tree-esque exploring of values, vim-like keybindings, full Moonscript support, watch expressions, the ability to launch your editor to a selected line, and the ability to run arbitrary code at different levels of the stack.
You can try it out here:
It's pretty stable and it's way better than just looking at a printout of a callstack. But, like I said, it doesn't yet support stepping through the code, only examining the state at a breakpoint or uncaught error.
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