[Openmcl-devel] consing

[Taoufik Dachraoui]

I did the following test with (fac 100) and (ack 3 12) and (ack 3 13) ;;
 ack is the ackermann function

CL-USER> (time (fac 100))
(FAC 100)
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
 3,864 bytes of memory allocated.
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000

CL-USER> (time (ack 3 12))
(ACK 3 12)
took 3,325 milliseconds (3.325 seconds) to run.
During that period, and with 1 available CPU core,
     3,360 milliseconds (3.360 seconds) were spent in user mode
         0 milliseconds (0.000 seconds) were spent in system mode
32765

(ack 3 13) fails with stack overflow, this I do not understand; (ack 3 12)
did not show any use of memory allocation
and (ack 3 13) fails for stack overflow?

Taoufik





On Tue, May 14, 2013 at 6:09 PM, Joshua TAYLOR <joshuaaaron at gmail.com>wrote:

> 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).
>
> 1) Although the machine stack stores things in machine memory (the
> program stack), when people talk about a program "cons'ing a lot" or
> allocating lots of memory, they're almost always talking about
> heap-allocated space.  Even though they use the word "cons'ing", it
> doesn't even have to be cons cells;  it's any heap allocation (so
> class objects, arrays, etc., are all included).  This code doesn't
> really need any heap space, so it's not consing.
> 2) Although the program has a stack, the program/machine stack is not
> (typically (does anyone know of any exceptions?)) implemented by a
> reusable abstract data structure known as a stack.  The push/pop model
> happens to be the same, but the program stack is just about
> incrementing and decrementing the CPU's stack pointer.
>
> //JT
> --
> Joshua Taylor, http://www.cs.rpi.edu/~tayloj/
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