[Openmcl-devel] consing

Taoufik Dachraoui dachraoui.taoufik at gmail.com
Tue May 14 15:52:30 UTC 2013


What is not true? I am not saying that stacks are conses; we can push and
pop elements from a stack and macroexpanding (PUSH 1 X) gives (SETQ X (CONS
1 X)); so the stack, used by pop/push, in CCL is implemented
using conses; we can implement stacks using arrays (no consing) if we wish
so.

Now, the reason I am asking, is that I am implementing an interpreter for a
small language and I am using 3 stacks with a lot of consing. I wanted to
find a solution so that I can avoid consing; I recalled when we call a
function the passed parameters are pushed into a stack (implemented with
registers ESP/EBP), I am wondering if I can find a way to use the
processor's stack as for function calls to avoid consing.

Or, how do you implement a VM using CCL for a new language? (any thing
offered by CCL even if it is not
standard would be acceptable).

Taoufik



On Tue, May 14, 2013 at 5:12 PM, Ron Garret <ron at flownet.com> wrote:

> This kind of question is better posed to a general Lisp newsgroup.  This
> list is specific to CCL (f.k.a.  OpenMCL).
>
> But the answer is simple:
>
> > pushing an element on the stack, (PUSH 1 X) is equivalent
> > to (SETQ X (CONS 1 X)),
>
> That is not true.  Stacks and cons cells are fundamentally different data
> structures.  You can build a stack out of cons cells, but you can't build
> cons cells out of a stack.  A stack is *strictly* a last-in-first-out data
> structure, which is the reason it doesn't need to be garbage collected.
>
> rg
>
> On May 14, 2013, at 3:37 AM, Taoufik Dachraoui wrote:
>
> > 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
> >
> > _______________________________________________
> > Openmcl-devel mailing list
> > Openmcl-devel at clozure.com
> > http://clozure.com/mailman/listinfo/openmcl-devel
>
>
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