Parser for off-side (indented) syntax

Off-side rule of syntax is when a scope is defined by indentation (like python). This parser can convert an input like

x 1 2
  x 3
    x 4 5 6
    x 7 8 9

x 10 11
  x 12

to a list with nested lists. Basically kinda like a Lisp without brackets.

Feel free to check test cases for some examples.

References

• stevekinney/dropbear
• (How to Write a (Lisp) Interpreter (in Python))
• AST Explorer