I've so far had good mileage with basically the following: (with-input-from-string (stream "1,2,3") (let ((*readtable* (copy-readtable)))

I've so far had good mileage with basically the following: (with-input-from-string (stream "1,2,3") (let ((*readtable* (copy-readtable))) (set-syntax-from-char #\, #\ ) (loop for num = (read stream nil nil) while num collect num)))