*print-base* — a radix. *print-radix* — a generalized boolean.

The initial value of *print-base* is 10. The initial value of *print-radix* is false.

*print-base* and *print-radix* control the printing of rationals. The value of *print-base* is called the current output base.

The value of *print-base* is the radix in which the printer will print rationals. For radices above 10, letters of the alphabet are used to represent digits above 9.

If the value of *print-radix* is true, the printer will print a radix specifier to indicate the radix in which it is printing a rational number. The radix specifier is always printed using lowercase letters. If *print-base* is 2, 8, or 16, then the radix specifier used is #b, #o, or #x, respectively. For integers, base ten is indicated by a trailing decimal point instead of a leading radix specifier; for ratios, #10r is used.

 (let ((*print-base* 24.) (*print-radix* t)) 
   (print 23.)) 
⊳ #24rN 
→ 23 
 (setq *print-base* 10) → 10 
 (setq *print-radix* nil) → NIL 
 (dotimes (i 35) 
    (let ((*print-base* (+ i 2)))           ;print the decimal number 40 
      (write 40)                            ;in each base from 2 to 36 
      (if (zerop (mod i 10)) (terpri) (format t " ")))) 
⊳ 101000 
⊳ 1111 220 130 104 55 50 44 40 37 34 
⊳ 31 2C 2A 28 26 24 22 20 1J 1I 
⊳ 1H 1G 1F 1E 1D 1C 1B 1A 19 18 
⊳ 17 16 15 14 
→ NIL 
 (dolist (pb '(2 3 8 10 16)) 
    (let ((*print-radix* t)                 ;print the integer 10 and 
          (*print-base* pb))                ;the ratio 1/10 in bases 2, 
     (format t "~&~S  ~S~%" 10 1/10)))        ;3, 8, 10, 16 
⊳ #b1010  #b1/1010 
⊳ #3r101  #3r1/101 
⊳ #o12  #o1/12 
⊳ 10.  #10r1/10 
⊳ #xA  #x1/A 
→ NIL

Might be bound by format, and write, write-to-string.

format, write, write-to-string