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From: wmb@MITCH.ENG.SUN.COM
Newsgroups: comp.lang.forth
Subject: Standard systems vs. standard programs
Message-ID: <9007201343.AA14784@ucbvax.Berkeley.EDU>
Date: 20 Jul 90 06:52:40 GMT
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Reply-To: wmb%MITCH.ENG.SUN.COM@SCFVM.GSFC.NASA.GOV
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JW>    I'd like an explanation from those of you who think that you can
JW>    take one of your current programs and will be able to run them
JW>    without change on anybody's ANSI system.

The ANS standard does not intend this, nor do I believe that it
would be possible to develop a standard, any standard, for which
this would be possible (because the present variations among extant
systems is reflected in the contents of current programs).

The portability goals of the ANS standard, as I understand them, are:

a) It should be possible to write a new program that will run without
   change on anybody's ANSI system.

b) It should be possible to run your old programs on the same vendors'
   systems that they used to run on, with little or no modification,
   even after those vendors' systems have been modified to conform to
   the ANS standard.

c) Where (b) is violated (i.e. where changes to old programs are
   required), those changes should be as mindless as possible.
   Definition of "mindless" by example:
	1) Redefining a word at the start of an application is
	   mindless.
	2) Globally substituting all occurrences of a word with
	   another word or phrase is mindless.
	3) Subtle changes, such tricky semantic differences in the way
	   that VOCABULARY works or the way in which : affects the
	   search order, are not mindless.  (That is why VOCABULARY
	   was renamed to WORDLIST ; the differences between its
	   implementation among extant systems are too tricky).

In other words, the ANS standard will not magically make your old
programs portable.  Old programs will be pretty much as portable
or as nonportable as they currently are (perhaps after a round of
"mindless" changes).

Another way of saying this is:  If an old program currently runs
on LMI Forth and F83 and F-PC, but not on MMS Forth or MacForth,
it will probably still run on LMI ANS Forth and ANS F83 and ANS F-PC,
but probably not on MMI ANS Forth or ANS MacForth.  And, it will be
easier to write a new program to run on all of the ANS Forths
systems than to write a new program to run of all of the current
nonANS Forths.

The reasons it will be easier to write a new portable program:

a) Precisely-defined alternatives to current "problem words" (e.g.
   NOT , / , VOCABULARY) have been created.

b) 32-bit systems are now allowed.

c) Rules for portable usage of addresses and address alignment have
   been articulated.

d) Wordsets for often-needed but previously-unspecified functions
   (e.g. floating point, file access, dynamic memory allocation,
   error handling, run-time search order, strings) have been added.

Mitch