Tail recursion in the Racket repl

gistfile1.txt

Welcome to Racket v5.3.6.
-> (define (factorial-no-tail n)
     (if (= n 0)
       1
       (* n (factorial-no-tail (- n 1)))))
-> (require racket/trace)
-> (trace factorial-no-tail)    
-> (factorial-no-tail 6)        
>(factorial-no-tail 6)
> (factorial-no-tail 5)
> >(factorial-no-tail 4)
> > (factorial-no-tail 3)
> > >(factorial-no-tail 2)
> > > (factorial-no-tail 1)
> > > >(factorial-no-tail 0)
< < < <1
< < < 1
< < <2
< < 6
< <24
< 120
<720
720
-> (define (factorial-tail n acc)
     (if (= n 0)
       acc
       (factorial-tail (- n 1) (* n acc))))
-> (trace factorial-tail)        
-> (factorial-tail 6 1)          
>(factorial-tail 6 1)
>(factorial-tail 5 6)
>(factorial-tail 4 30)
>(factorial-tail 3 120)
>(factorial-tail 2 360)
>(factorial-tail 1 720)
>(factorial-tail 0 720)
<720
720

I actually have (require racket/trace) in my .racketrc, but I figured I'd show it for completeness/to avoid confusing people.