Open tree-fun.rkt in DrRacket (e.g., `drracket tree-fun.rkt`).

Then run it and try
  (fun '(1 2 3 4 5 6 7))
and
  (fun qbf)
in the interactive area.


Minor implementation note:
I made/used "string-to-scheme-list.sh" because I didn't yet find a way
in Scheme/Racket to convert a string to a list of characters (which I know
is suspect because Unicode code-points and extended grapheme clusters etc,
which one do I mean, but at least it's clear for this fixed ASCII text):
  echo 'The quick brown fox jumps over the lazy dog' | ./string-to-scheme-list.sh
-Isaac