<HTML><BODY>I compared parameterize with lexical var ---- > (require rackunit) > (define my-parameter (make-parameter (box 0))) > (time    (parameterize ([my-parameter (box 0)])      (for ([x (in-range 10000000)])        (set-box! (my-parameter)                  (add1 (unbox (my-parameter)))))      (check-equal? (unbox (my-parameter)) 10000000))) cpu time: 3578 real time: 3610 gc time: 0 > (time    (let ([my-parameter (box 0)])      (for ([x (in-range 10000000)])        (set-box! my-parameter                  (add1 (unbox my-parameter))))      (check-equal? (unbox my-parameter) 10000000))) cpu time: 47 real time: 47 gc time: 0 ---- 100 times difference! The same experiment with Common Lisp (SBCL): ---- CL-USER> (setf *a* (list 0)) (0) CL-USER> (time (progn (loop :for i :from 0 :below 10000000             :do (setf (car *a*) (+ 1 (car *a*)))) (= (car *a*) 10000000))) Evaluation took:   0.063 seconds of real time   0.062500 seconds of total run time (0.062500 user, 0.000000 system)   98.41% CPU   172,464,541 processor cycles   0 bytes consed   T CL-USER> (let ((a (list 0))) (time (loop :for i :from 0 :below 10000000             :do (setf (car a) (+ 1 (car a))))) (= (car a) 10000000))               Evaluation took:   0.047 seconds of real time   0.046875 seconds of total run time (0.046875 user, 0.000000 system)   100.00% CPU   132,098,942 processor cycles   0 bytes consed   T ---- Only 1.5 times. Is it undesirable to use parameterize as replacement for common lisp special variables? What is it designed for then? -- Roman Klochkov</BODY></HTML>