Re: How does runtime stack work?

[david kerns]

Generating machine code is usually considered to be the work of a compiler,
for languages such as C and FORTRAN. (showing my age)
Scripted or interpreted languages typically use an intermediate "language"
or byte code, BASIC, Python, ... awk ;)

On Fri, May 21, 2021 at 6:09 AM Peng Yu <pengyu.ut@gmail.com> wrote:

> OK. Thanks. I would like to understand how gawk is implemented internally.
>
> So byte code implementation is slower than directly generating machine
> code but is easier to implement?
>
> On 5/21/21, arnold@skeeve.com <arnold@skeeve.com> wrote:
> > Peng Yu <pengyu.ut@gmail.com> wrote:
> >
> >> Hi,
> >>
> >> I see a stack is used in gawk. I don't understand what this is used
> >> for. Could anybody help explain? Thanks.
> >
> > Out of curiosity, why do you ask?
> >
> > To briefly answer the question, gawk reads the program and converts
> > it into an internal form, often called "byte code". The internal form
> > represents instructions for a "virtual machine" that is stack based.
> > Operands are pushed onto the stack. Operators pop the operands, do the
> > operation, and push the result back onto the stack. For example,
> >
> >       x = 3 + 5
> >
> > would turn into something like:
> >
> >       PUSH    3
> >       PUSH    5
> >       ADD             # 3 and 5 are popped off the stack, 8 is pushed on
> it
> >       STORE   x       # 8 popped off the stack and stored into 'x'
> >
> > This is one of several standard mechanisms for implementing programming
> > language interpreters.
> >
> > There have been hardware computers that are stack based as well,
> > although I am not sure which modern architectures, if any, are
> > stack based.
> >
> > HTH,
> >
> > Arnold
> >
>
>
> --
> Regards,
> Peng
>
>