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Forth doesn't use CALL it uses JMP

Similar Threaded Interpretive Languages run an inner loop that does this
pseudo code :
(from Threaded Interpretive Languages: Their Design and Implementation
by R. G. Loeliger)

COLON:
    PSH I -> RS
    WA -> I
    JMP NEXT
SEMI:
    POP RS -> I
NEXT:
    @I -> WA
    I += 2
RUN:
    @WA -> CA
    WA += 2
    CA -> PC

RS is the stack PC is the program counter, procedures JMP to NEXT or
SEMI when they are done
I is the indirection pointer, WA is the word address (the nomenclature
for procedure)
The 2s are there because this code assumes 16bit addressing, @ is
indirection
CA is the call address

so DUP is a word defined as (it copies the item on the top of the stack
back to the top of the stack
execute is a type marker, you can also have constant & colon

dup:
    execute
    POP SP -> A
    PUSH A -> SP
     PUSH A -> SP
   JMP NEXT


that's all very well but you then extend the assembler parts with new
words made from the WAs  (colon is the type marker for this) SEMI is
where it JMPs to at the end

moddiv:
    colon
    divmod
    swop
    semi



I wrote a TIL in AVR assembler last summer but I've waiting to go on
holiday this year so I can write some applications in it now I have a
dev board :>