Web loop UI

[shachaf]

I just found out about --loop, which can replace the manual inotify loop I was running before. But I think there could be an even more useful loop mode: A small web server that watches for file changes, automatically reruns the program, and either displays errors or reloads the diagram. This would let me just open my editor and browser side-by-side and make changes in my editor, without having to switch to my browser to reload or to my terminal to see errors. This could be implemented either as a built-in loop mode or as a small external program.