It doesn't work correctly. Example:
print parse_expr("1+2/3/4-5*6")
(+ 1 (/ 2 (/ 3 (- 4 (* 5 6))))) print parse_expr("1+2/3/4-5*6")
(+ 1 (/ 2 (/ 3 (- 4 (* 5 6)))))