[Openmcl-devel] consing

Ron Garret ron at flownet.com
Tue May 14 16:53:21 UTC 2013


Well, by implementing a stack of course.  There are a lot of good books and articles about how to implement compilers.  Have you read any of them?

rg

On May 14, 2013, at 9:03 AM, Taoufik Dachraoui wrote:

> I am not expecting the compiler to use consing, I want to do the same thing as the compiler is doing, how to do it?
> 
> Taoufik
> 
> 
> On Tue, May 14, 2013 at 6:01 PM, Tom Emerson <tremerson at gmail.com> wrote:
> If you disassemble your fact function you'll see that there is no consing going on: the machine stack is being used directly. I'm not sure why you would expect the compiler to use conses for this.
> 
> 
> 
> On Tue, May 14, 2013 at 11:52 AM, Taoufik Dachraoui <dachraoui.taoufik at gmail.com> wrote:
> 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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> 
> 
> 
> -- 
> Tom Emerson
> tremerson at gmail.com
> http://www.dreamersrealm.net/tree
> 

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