[Openmcl-devel] consing

Taoufik Dachraoui dachraoui.taoufik at gmail.com
Tue May 14 10:37:08 UTC 2013


Hi

This is probably simple but I could not figure out the explanation, I hope
that
someone could help me out

CL-USER> (defun fac (n) (if (= n 0) 1 (* n (fac (- n 1)))))
FAC
CL-USER> (time (fac 3))
(FAC 3)
took 0 milliseconds (0.000 seconds) to run.
During that period, and with 1 available CPU core,
     0 milliseconds (0.000 seconds) were spent in user mode
     0 milliseconds (0.000 seconds) were spent in system mode
6

As you can see, there is no consing when FAC is called

Now, knowing that pushing an element on the stack, (PUSH 1 X) is equivalent
to (SETQ X (CONS 1 X)), and since FAC is using a stack and thus pushing
values on the stack why there is no consing when (FAC 3) is called?

I believe there is a simple explanation but I could not figure it out

Kind regards
Taoufik
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