Advent of Code 2019 Day 1, Part 2

01.lisp

(defun fuel-for-mass (mass)
  (- (floor mass 3) 2))

(defun total-fuel-for-mass (mass)
  (loop :for current-mass = (fuel-for-mass mass)
          :then (fuel-for-mass current-mass)
        :until (minusp current-mass)
        :sum current-mass))

(defun part-2 (stream)
  (loop :for line = (read-line stream nil)
        :while line
        :sum (total-fuel-for-mass (parse-integer line))))