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From: wsbusup4@rw5.urc.tue.nl (Jan Stout)
Newsgroups: comp.lang.forth
Subject: Problems not solved by START:
Message-ID: <586@rc6.urc.tue.nl>
Date: 6 May 91 10:55:22 GMT
Sender: news@rc6.urc.tue.nl
Organization: Eindhoven University of Technology, The Netherlands
Lines: 37


   The function of START:, as I do perceive, is to factor
the naming process from the definition process, which will
allow the creation of nameless definitions.
   In the rationale that accompanies START:, J Hopkins states:

  `... expert Forth programmers have exploited intimate knowledge
   of their systems to generate unnamed code fragments. Now this
   function has been named and can be used in a portable program'

   I'm not sure wheter this degree of portability is possible using
START: on it's own. In fact, if  we take a closer look at the example
construct (CMD: ;CMD), supplied by JH, we find:

   : :CMD ( n -- ) START: ... ;
   : ;CMD ( -- ) POSTPONE EXIT  POSTPONE [ ; IMMEDIATE

   Written this way, me must infer that the only actions necessary to
conclude the START: are an EXIT and a [ (to enter interpretation state).
   However when we check ;'s definition, we find that besides performing
EXIT and entering compilation state ; also ENDS THE CURRENT DEFINITION,
which IMHO may be more than a NOOP. A LOCALs mechanism e.g. will require
the addition of some extra memory recovering words to the definition of ;.
   I think the only way to hide this `intimate knowledge' (system dependency)
is to add yet another word called ;END (or START; (*)) that will perform
;'s function without the name processing.

Jan Stout,
wsbusup4@urc.tue.nl

(*) I'm not sure about the etymology of START: ;
does START: mean we're STARTing a definition with the : as a mere Brodie-like
syntax convention, suggesting high level Forth will follow, or should the :
(colon) be emphasized, stressing the fact that START: is a part of :?
   In the first case I'd prefer ;END, whereas in the latter START; seems more
appropriate.