absolutely useless Lisp-like interpreter written in Python

A small Lisp-like language implemented in Python. Just because.

• Primitives: (true false nil SymbolReferences 'Symbols 42 1.6666 "strings")
• Variables and constants:

  ((let (x (y 0)))
   (const ((z 1.25)))
   (= x nil)                  ;; true
   (set x 3)                  ;; 3
   (set y (* 2 x z))          ;; 7.5

• Floating-point arithmetic: + - * /
• Real comparison: < <= > >=
• Expr comparison: = !=
• Bool operators: ! && ||
• Bitwise operators on integer Real values: ~ & |
• λ-expressions:

  ((let ((add (lambda (a b) (+ a b)))))
   (add 3 2)                  ;; 5
   (defun sub (a b) (- a b))  ;; shorthand form
   (sub 5 3)                  ;; 2

• while loops:

  ((let ((i 0) (M 5)))
   (while (< i M)                ;; (nil 1 nil 2 nil 3 nil 4 nil 5)
    (send "%d. Hello!" (+ 1 i))  ;; nil
    (set i (+ 1 i))))            ;; (+ 1 i)

• Conditional expressions
• &optional and &rest parameters
• Proper quote/' on any Expr, not only Symbols
• Selector expressions:

  ((let ((my-list (1 2 3))
         (fake-dict ('i 0 'j 1 'k 2))
         (my-string "hello \"world\"!"))
   ([0] my-list)             ;; 1
   ([rev (rg 0 2)] my-list)  ;; (3 2 1)
   (['i 'k] fake-dict)
   ([.length 0] my-string))  ;; (14 "h")

• Python interop

lisp.errors.LispError: el nombre de la función no puede ser un símbolo literal. Utiliza la notación `(lambda (a b) (+ a b))` para declarar una función anónima en la línea 4, columna 16
   4          (defun '+ (a b) (+ a b))
   \-----------------^^

• Exception messages intend to be actually useful.
• Works at least 68% of the time!!