RE: [External] : Tip: Debugging with function `message-box'

[Drew Adams]

> When there is something wrong I am also using C-u C-M-x to instrument
> the function then I can go step by step verifying what is happening.

1. That's `edebug', one of the Lisp debuggers for Emacs.

https://www.gnu.org/software/emacs/manual/html_node/elisp/Edebug.html

2. Plain `debug' is another Lisp debugger for Emacs.

https://www.gnu.org/software/emacs/manual/html_node/elisp/Debugger.html

 * `debug-on-entry' to debug on entry to a function,
   including a built-in (coded in C).  (And some C
   code calls Lisp functions.)

 * Non-nil `debug-on-error', to just see a backtrace.

 * Place calls to `debug' in code as breakpoints,
   i.e., places where the debugger is entered.

3. GUD is another debugger you can use with Emacs.

https://www.gnu.org/software/emacs/manual/html_node/emacs/Debuggers.html
____

They all let you go step by step.