\ Stand-alone self-hosted compiler for a subroutine threaded Forth
\ that can operate well with the 8-bit PIC18 Forth.  This is written
\ in a subset of standard Forth so it works on a 16-bit VM.

variable here
variable last  
16 base !

\ Words used for compilation:
\    variable base ! : ; @ dup >r r> 2/ - and or postpone
\  
\ Machine code kernel primitives: 
\    dolit
  
: cell 4 ;  
: , here @ dup >r ! r> 1 cell + ;
    
  
\ PIC18 specific compile and literal.
: compile \ XT --
    here @ - 2/ 1 -  \ relative word offset
    07FF and
    D800 or , ; \ relative branch instruction.

: literal \ n --
    postpone dolit , ;

: postpone \ --
    parse find compile ;

\ For the subroutine threaded forth, execution tokens (XT) point to
\ executable machine code.  The compilation semantics points to the XT
\ of the word's compiler.  A dictionary entry looks like this:

    \ LINK pointer to next record
    \ XT   pointer to executable code of interpret semantics
    \ CT                                 compile
    \ NAME padded pascal string

\ The dictionary does not contain in-line machine code - only a
\ reference.  This allows the entire dictionary to be wiped or
\ implemented off-target without disturbing machine code.
    
: rec>link @ ;
: rec>xt   1 cell + @ ;
: rec>ct   2 cell + @ ;
: rec>name 3 cell + ;    

\ Compare two strings.
: string= \ s    
    
\ Lookup in the dictionary to find the execution token.
: find \ string -- xt
    
    ;
  
: xt>ct \ xt -- ct