24. Host Environment

  The host system can be identified in several ways:

  A%=0:X%=1:os%=((USR&FFF4)AND&FF00)DIV256 returns 8 to indicate UNIX and UNIX
  style pathnames director/filename.ext.

  If OSBYTE 0 returns 8, then INKEY-256 returns:
      &FE: NetBSD           &F6: OpenBSD
      &FB: BeOS             &F5: Amiga
      &F9: Linux            &F4: GNU FreeBSD
      &F8: MacOS            &F3: GNU
      &F7: FreeBSD      
      &Bx: PDP11 Unix, &B5=Unix v5, &B6=Unix v6, &B7=Unix v7, &B8=Unix v8
                       &B9=BSD2.9,  &BB=BSD2.11
           (interim: &B0=RT11/RSX/RSTS)
           
  A%=0:Y%=0:fs%=(USR&FFDA)AND&FF returns 24 to indicate a UNIX filing system.

  [OPT 0:NOP:] assembles &A0 to identify the CPU as a PDP-11.


25. Technical notes

   ARM  BASIC V double-tokens are recognised internally, but are  listed  as
   the single-token components.

   Internal memory:
     ^@%-512 : String buffer, string can be fetched with $(^@%-512) or $(PAGE-&300)
     ^@%-256 : Input buffer, string can be fetched with $(^@%-256) or $(PAGE-&200)
     ^@%     : Integer variables
     ^@%+108 : Pointers to dynamic variables
     ^@%+242 : Memory structure pointers
     ^@%+256 : Default PAGE
   
     A%=EVAL("0:"+text$):token$=$(^@%-510) will tokenise text$ and put it in token$
   
   Variables in the heap, always word aligned:
        ^variable (word aligned) ---v
   link, name,           &00, (pad), b0-b7, b8-b15, b16-b23, b24-b31, b32-b39, &00
   link, name, '%',      &00, (pad), b0-b7, b8-b15, b16-b23, b24-b31
   link, name, '$',      &00, (pad), b0-b7, b8-b15, length,  space
   link, name, '(',      &00, (pad)
   link, name, '%', '(', &00, (pad)
   link, name, '$', '(', &00, (pad)
                      ^variable() ---^

     name, ['%', '$'], '(', &00, num of dims, dim, {dim...}, data, {data...}
                  ^variable() ---^
                               ^variable(dims{, dims...}) ---^
   
Stack layout:

Top of stack:
  cmdret, &0000 - empty
  cmdret, &00nn - token
  cmdret, &nnxx - data

Stack contents:
  cmdret, {looping and saved structures}, {saved PROC/FN}, {local variables}, &0000

On exit from subroutine, all these are popped off
tknFOR, step[6], limit[5], vartype[1], ^variable, saved r5
tknREPEAT, saved r5
tkkGOSUB, saved r5
tknERROR, saved SV_STACK, saved SV_ONERR
tknDATA, saved SV_DATA

could use table instead of compares:
equb tknREPEAT,tknGOSUB,tknDATA,tknERROR,tknFOR
equw         1,       1,SV_DATA,SV_STACK,    16
\ pop off    1,       1,      1,       2,    16

or:
equb tknREPEAT,tknGOSUB,tknDATA,tknERROR,tknFOR
calculate    1,       1,      1,       2,    16
pop to       -,       -,SV_DATA,SV_STACK,     -


Subroutine structures are after any looping/etc structures
tknPROC/tknFN, {any local variables}, &0000, saved SVSTACK, saved LPTR

Local variables
{type, addr, data} stacked local data
&0000                           - end of stacked data
&00nn <&80
&00nn >&7F                      - token
&0xxx                           - number
&8xxx                           - string
&0100, address, b0-b7           - byte (could squash into &01xx?)
&0200, address, b0-b15          - 16-bit integer
&0400, address, b0-b15, b16-b31 - 32-bit integer
&05ee, address, mantis, mantis  - real with exponent in {type} word
(could optimise to &0n00 and loop 1,2,3,4,5... allowing 3 and 6+)
&80nn, address, string, align   - string
&81nn, address, string, align   - $address
&82nn, address, string, align   - $$address
&2xxx, address,                 - reserved for RETURN variable