Re: Extending Applesoft with Ampersand routines.

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

Ivan X <ivan@ivanx.com> wrote:
> On Tuesday, March 12, 2013 4:32:35 PM UTC-4, Michael J. Mahon wrote:
>> BLuRry 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
> 
> This is awesome. Thanks, Michael.
> 
> When I did Slammer, since I figured it was an Applesoft programming tool,
> I deliberately kept it away from the ampersand vector (though it does use
> the CTRL-Y vector at $3F8). This would be a cool thing to deliver via
> Slammer and have all the ampersand processing without needing to BLOAD
> anything; I might have to try to do that!

Glad you like it!

I wanted to provide a simple, easy to use interface to NadaNet
transactions, and the ampersand interface seemed made to order.

Since I was aiming for maximum functionality in minimum space, including
exception handling and output parameters, I had to get creative with
parsing and semantics.

I'm particularly proud of piggybacking on the standard "OUT OF DATA ERROR"
for my network "DATA ERROR" message for practically no cost. ;-)

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