[Coco] USRx() and adding more parameters?

[Sean Conner]

It was thus said that the Great William Astle via Coco once stated:
> On 2025-11-04 20:14, Allen Huffman via Coco wrote:
> >The BASIC ROM has the USR function:
> >
> >DEF USR0=&H3F00
> >
> >A=USR0(42)
> >
> >It accepts one parameter.
> >
> >Since it jumps from BASIC into the USR assembly, couldn’t that code just 
> >parse a “,” and more numbers, allowing it to accept whatever needed to 
> >be passed in?
> >
> >A=USR0(1,2,3,4)
> 
> Almost. It would have to look like:
> 
> A=USR0(1),2,3,4
> 
> The closing parenthesis is already validated by the time the USR handler 
> starts.

  I did a proof-of-concept:

                include "basic.i"

                org     $7F00

                .opt    basic defusr0 pokew

pokew           jsr     INTCVT
                std     $F4	; unused by BASIC
                jsr     $B26D   ; skip comma
                jsr     $B156   ; evaluate expression
                jsr     INTCVT  ; get value
                std     $F6	; unused by BASIC
                clra
                clrb
                jmp     GIVABF
                end

basic.i defines INTCVT and GIVABF.  This works.  BASIC program:

10 DATA189,179,237,221,244,189,178,109,189,177,86,189,179,237,221,246,79,95,126, 180,244
20 CLEAR200,32511:FORA=32512TO32532:READB:POKEA,B:NEXT:DEFUSR0=32512
30 X=USR0(1234),5678:PRINT"HELLO"
40 PRINTPEEK(&HF4)*256+PEEK(&HF5)
50 PRINTPEEK(&HF6)*256+PEEK(&HF7)

  -spc