undent | ️ Dedent and format multiline strings | Code Quality library

There are a number of problems with your function, including some vary fundamental elisp requirements. Highly recommend reading the Emacs Lisp Reference Manual (bundled with emacs). If you are new to programming and lisp, you may also find An Introduction to Emacs Lisp useful (also bundled with Emacs).

A few things to read about which will probably help

• Read the section on the command loop from the elisp reference. In particular, look at the node which describes how to define a new command and the use of 'interactive', which you will need if you want to bind your function to a key or call it with M-x.

• Read the section on variables from the lisp reference and understand variable scope (local v global). Look at using 'let' rather than 'setq' and what the difference is.

• Read the section on 'positions' in the elisp reference. In particular, look at 'save-excursion' and 'save-restriction'. Understanding how to define and use the region is also important.

It isn't clear if your writing this function just as a learning exercise or not. However, just in case you are doing it because it is something you need to do rather than just something to learn elisp, be sure to go through the Emacs manual and index. What you appear to need is a common and fairly well supported requirement. It can get a little complicated if programming modes are involved (as opposed to plain text). However, with emacs, if what you need seems like something which would be a common requirement, you can be fairly confident it is already there - you just need to find it (which can be a challenge at first).

A common convention is for functions/commands to be defined which act 'in reverse' when supplied with a negative or universal argument. Any command which has this ability can also be called as a function in elisp code with the argument necessary to get that behaviour, so understanding the inter-play between commands, functions and calling conventions is important.