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From: wmb@MITCH.ENG.SUN.COM
Newsgroups: comp.lang.forth
Subject: PostScript is NOT based on Forth
Message-ID: <9101031535.AA12653@ucbvax.Berkeley.EDU>
Date: 2 Jan 91 20:10:32 GMT
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Reply-To: wmb%MITCH.ENG.SUN.COM@SCFVM.GSFC.NASA.GOV
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> I have other dream machines.
> A muilti-FORTH engine running a NEXTSTEP workstation, for one.
> My reasoning is that with Display Postscript being based on FORTH
> a FORTH engine auta do just fine.

PostScript in NOT based on Forth.  Quoting from the Preface in the
_PostScript Language Reference Manual_ (The "Red Book"):

        Although the Design System language [the precursor to PostScript]
        and its successors bear a superficial resemblance to the FORTH
        programming language, their conception and development were
        entirely independent of FORTH.

I believe this.  I really really do.  I know both Forth and PostScript
rather well, and I believe that there are *profound* differences in the
guts of the two languages.  The similarity starts and ends with "both
languages have postfix syntax".  The execution models are so different
that there is no particular reason to believe that a good Forth engine
is necessarily a good PostScript engine.  (A particular Forth engine
might turn out to be an okay PostScript engine just by virtue of being
generally a fast machine, but the stack optimizations of the Forth
engines I know of don't match the PostScript stack requirements very
well, nor do the optimization for handling threading).

In my view, the Magic-L language (essentially STOIC with Pascal-like syntax),
even though its syntax is not postfix at all, is much much closer to Forth
then PostScript.

The order in which you type words to compose a program has only a minor
influence on the optimum execution architecture for a language.  The type
structure of a language is much more important (PostScript has typed
objects, Forth has untyped "cells"), and the binding is more important
too (PostScript defaults to late binding, Forth to early binding).

Mitch Bradley, wmb@Eng.Sun.COM