Re: About the FOR loop semantic action

[Ilyes Gouta]

Hi,

Thanks Laurence for your comments.

> I don't know how C compilers do this, but you could look at how I

I think C compilers generate semantic trees, instead of executing the
actions, that then are passed to the back-end to emit CPU opcodes.

> implemented loops in GNU 3DLDF.  It was not particularly difficult.  The
> basic idea is:  Read the loop, put it into a buffer, put code at the end
> of the buffer for your conditional and start reading from the buffer

Hmm.. So bison is able to read from data buffers instead of a FILE*.
How can I achieve that?

> > if a given condition isn't met? It's
> > typically useful for the "if then else" closure, i.e:
> >
> > if_stmt:
> >     IF expr { update(&($2)); } block { reset(); }
> > ;
> >
> > where block won't be parsed/executed if the expr isn't valid.
>
> I think it's usually not a good idea to execute code in the middle of

I agree, but I didn't find another way, yet. Back to for loops, if I'm
going to copy my block into a temporary buffer then I'll have to do
something similar, i.e executing an action in the middle of a rule, at
least to mark the beginning of a block and its end, i.e:

block:
    '{' { begin_marker(); } declarations statements { end_marker(); } '}'
;

to save the content of the entire block and re-execute it as long as
the condition is valid.

Any thoughts?

BR,
Ilyes Gouta.