Re: Extending Applesoft with Ampersand routines.

[Michael J. Mahon <mjmahon@aol.com>]

BLuRry <brendan.robert@gmail.com> wrote:
> I'm starting this as a new thread since Bill Buckels asked a very good
> question as a response to my smart-ass response to a cross-post.
> 
> Here is what I know about ampersand routines from a high-level:
> 
> You register your ampersand routine handler as a memory pointer, and your
> routine is called by the applesoft interperter (only at runtime) when it
> encounters the & sign.
> 
> Applesoft pointers indicate the current memory address where the parser
> was looking (I can't remember if it is the location where & occurs or the
> memory location just after it).
> 
> It is up to your routine to parse as much or as little as it wants, and I
> believe your parsing routine has to update the applesoft pointer(s) as
> well.  This allows you to do some very wonderful and complex things, or
> also very simple ones.
> 
> And this is the part that eluded me when I experimented with this stuff
> in the 90's: Your parser will encounter tokenized applesoft statements. 
> That means if your code looks like: &HOME then the actual data will be
> the tokens &(0xAF) and HOME (0x97).  You can use this to your advantage
> by reusing applesoft tokens for your amp commands instead of having to
> compare letter after letter (which is the case if the characters do not
> have the hi-bit set)  Some tokens have the open paren or equal sign as
> part of the token as well.
> 
> As for the ins and outs of how to return out of an ampersand command,
> again it goes back to the applesoft zero-page locations.  I can't
> remember if you have to clear/set the carry as a status bit like you do
> in other Apple firmware routines but it wouldn't surprise me if CLC meant
> there was no error and SEC meant there was.
> 
> Also, here's a list of all the applesoft tokens as well as my applesoft
> de-tokenizer routine:
> 
> http://sourceforge.net/p/java-ace/code/285/tree/jace/src/jace/applesoft/Command.java
> 
> I hope this helps.  I can dig up some better information if this is insufficient.
> 
> -Brendan

No, there's no automatic error handling--you have to explicitly report any
errors. 

I replied in the original thread before noticing your new one. ;-)

Check out the AMPERNADA module in my NadaNet source for a compact, quite
capable ampersand handler. 

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon