Quick help: look at Emacs/your editor menu for commands, in Emacs type "v" to go to the buggy line, fix your bug, compile the function (C-c C-c), type "r" on th

Quick help: look at Emacs/your editor menu for commands, in Emacs type "v" to go to the buggy line, fix your bug, compile the function (C-c C-c), type "r" on the buggy frame to restart it from where it failed, and voilà. If you were processing something costly, you didn't have to restart it from zero.