Re: [OpenBIOS] C's continue statement in Forth?

[Programmingkid]

On Aug 25, 2012, at 8:19 AM, [e-mail] wrote:
> > I was wondering if there is a way to implement C's continue  
> > statement in Forth. I have this loop, and some times I only want to  
> > execute part of it, and then continue on to the next iteration  
> > without finishing the current iteration. Is there any way of doing  
> > this in OpenBIOS?
>
> It certainly can be done.  But it sounds like you are making a
> word with a very big body; this is not the Forth way.  Instead,
> factor your words into smaller words, for example, pull the loop
> body (the part between WHILE and REPEAT) into a separate word.
> It then becomes trivial to do your "continue" (and it will also
> be much more readable!)
> > begin
> > \ condition
> > while
> >
> > \  conditional code
> > if
> >    CONTINUE		\ skip rest of loop
> > then
> >
> > \ rest of loop ...
> >
> > repeat
>
> You don't have anything in here that "increases" the condition
> (increases some counter, follows a pointer, whatever).  Typically
> you would have that just before the REPEAT, but your example makes
> it seem you have it between the BEGIN and WHILE.  So your code is:
>
> BEGIN cond WHILE smth IF CONTINUE THEN rest REPEAT
>
> which you can write as
>
> BEGIN cond WHILE smth 0= IF rest THEN REPEAT
>
> (and if you do have an "increment" just before the REPEAT, which
> you want to run on CONTINUE, you can put it between the THEN and
> REPEAT in the modified example).
>
> But, let's build a CONTINUE like you described, just for fun.
> Let's look at the structure words you used:
>
> BEGIN ( C: -- dest )
> WHILE ( C: dest -- orig dest )
> REPEAT ( C: orig dest -- )
>
> You want to use your CONTINUE word between WHILE and REPEAT, and
> it should jump back to "dest"; at compile time, it should not drop
> the "dest" from the compilation stack.  So its stack diagram is
>
> CONTINUE ( C: orig dest -- orig dest )
>
> or just
>
> CONTINUE ( C: dest -- dest )
>
> For doing an unconditional jump back, there is AGAIN, which is
>
> AGAIN ( C: dest -- )
>
> That eats the dest from the compilation stack though, so we want
> to duplicate it first, using CS-DUP
>
> CS-DUP ( C: dest -- dest dest )
>
> Not every system has that; just make it from CS-PICK, like so:
>
> : CS-DUP  0 CS-PICK ; IMMEDIATE
>
> And then let's do CONTINUE itself:
>
> : CONTINUE  CS-DUP POSTPONE AGAIN ; IMMEDIATE
>
> Or you might want a ?CONTINUE which does the equivalent of
> IF CONTINUE THEN:
>
> : ?CONTINUE  POSTPONE 0= CS-DUP POSTPONE UNTIL ; IMMEDIATE
>
> Hope this helps,
>
> Segher

You are right. My code was a little too long, so refactoring it fixed the problem. I guess I was still programming like a C programmer still. Thanks for the help.