One of the most complex parts of a Forth engine is dodoes, i.e.,
the chunk of code executed by every word defined by a
CREATE...DOES> pair; actually with primitive-centric code,
this is only needed if the xt of the word is executed. The main
problem here is: How to find the Forth code to be executed, i.e. the
code after the DOES> (the DOES>-code)? There are two
solutions:
In fig-Forth the code field points directly to the dodoes and the
DOES>-code address is stored in the cell after the code address
(i.e. at CFA cell+). It may seem that this solution is
illegal in the Forth-79 and all later standards, because in fig-Forth
this address lies in the body (which is illegal in these
standards). However, by making the code field larger for all words this
solution becomes legal again. We use this approach. Leaving a cell
unused in most words is a bit wasteful, but on the machines we are
targeting this is hardly a problem.