Log of my last 3 minutes of activity:

  This is the TXR Lisp interactive listener of TXR 197.
  Quit with :quit or Ctrl-D on empty line. Ctrl-X ? for cheatsheet.
  1> (defun add-text-padding (str nspaces : newline-p)
       (let ((padding `\n@(mkstring nspaces)`))
         (when newline-p
           (set str `\n@str`))
         (regsub #/\n/ padding str)))
  add-text-padding
  2> (add-text-padding "hello\nworld")
  ** (expr-2:1) add-text-padding: too few arguments
  3> (add-text-padding "hello\nworld" 3)
  "hello\n   world"
  4> (add-text-padding "hello\nworld" 3 t)
  "\n   hello\n   world"

Note how (mkstring n) makes a string of n spaces by default; if you want a different character, specify it as a second argument.

I've never heard of trivial-update, but TXR has something like it built-in that I independently invented called upd:

  1> (defvar a 0)
  a
  2> (upd a (+ 2) (* 3))
  6
  3> a
  6

upd implicitly uses the syntax of the partial application operator op to create a pipeline of partial applications. To get such a pipeline by itself as a function, opip can be used; upd is simply the result of wanting a place-mutating operator that takes a place's value through an opip pipe and then writes the result back in.

TXR Lisp also has a well-featured command line option parsing library built-in:

http://nongnu.org/txr/txr-manpage.html#N-02C70C38