                   (if (zerop x)
                            acc
                            (sum-aux (+ acc x) (- x 1))))
                      (sum (n)
                        (sum-aux 0 n)))
               (sum 1000000))
Control stack guard page temporarily disabled: proceed with caution
; Debugger entered on #&lt;SB-KERNEL::CONTROL-STACK-EXHAUSTED {1004F12E73}&gt;
[1] POFTHEDAY&gt; 
; Evaluation aborted on #&lt;SB-KERNEL::CONTROL-STACK-EXHAUSTED {1004F12E73}&gt;

POFTHEDAY&gt; (tco:with-tail-call-optimi