Forth Postscript Relationship

ForthLanguage and PostScript appear superficially similar, since both languages use a mostly postfix-based syntax (see PostfixNotation). Since Forth predates PostScript by quite a few years, PostScript is often assumed to be descended from Forth.

From GroundBreakingLanguages:

According to JohnWarnock?, inventor of PostScript, this is not the case.

Postscript is a graphical page description language invented by ChuckGetsche? and JohnWarnock? (the President and CEO of Adobe). Its syntax looks a little bit like Forth, because it is derived from Forth; however, Postscript's internal implementation has nothing to do with Forth. (from http://www.google.com/search?q=cache:sysadmin.habitue.net/html/v05/i07/a6.htm+postscript+forth+John+Warnock&hl=en ).
JohnWarnock? states in the preface to 'PostScript Language Reference Manual' (1st Edition): "Although the Design System language and its successors bear a superficial resemblance to the Forth programming language, their conception and development were entirely independent of Forth."
"Does not contain code from forth" does not mean "is not descended from forth". C is considered to belong in the Algol family even though it doesn't contain code from an implementation of Algol. PostScript wouldn't be what it is without forth.
It seems to me that Forth is to stacks what LispLanguage is to lists. Forth demonstrated the advantages of a stack-centric paradigm in which each pushed or popped item could be evaluated as an expression or a primitive. Postscript reflects the application of that paradigm to the world of typography, 2-d graphics, and page layout. My own recollection is that Postscript's primary contribution was the use of splines to describe character glyphs, allowing them to be effectively rendered at virtually any resolution desired. If anything, Postscript owes more to TexLanguage and DonaldKnuth than to Forth. I view the stack-based language paradigm as a convenient afterthought rather than a central organizing principle.

I also think we should note the contribution that OwenDensmore?, at Sun, made in demonstrating how to use Postscript dictionaries to create a dynamically-bound object-oriented runtime environment. This was the fundamental premise of the Sun window server that ultimately became the NetworkExtensibleWindowSystem. Owen and I discussed his "crazy" idea at a poolside table at the now-demolished Hyatt Palo Alto, on El Camino. I told him that it made sense to me, we scribbled furiously on napkins, and I helped him see how he might adopt some learnings from Smalltalk. It was one of those afternoons that could only have happened at that time in that place in that culture. -- TomStambaugh

I've extracted Owen Densmore's paper from the news.tape.tar (marked PD), "Object Oriented programming in NeWS", and uploaded it: http://code.google.com/p/xpost/downloads/detail?name=monterey86.pdf It would require some modification to run in other postscript environments, but not much, I think. It was developed after the 1st Edition Postscript manual but before the second, so it's considered a Level 1.5 Postscript environment. It uses dictionaries freely, but the << /Level-2 (syntax) >> had not yet been invented. So it uses a number of nonstandard operators for dictionary construct. These would need to be simulated or the routines rewritten to use Level 2 syntax. -- luserdroog
I think the "because it is derived from Forth" statement says a lot. ;-> he is talking about the syntax, not the implementation and conception

I've generally described Postscript as "FORTH, with an impressive rendering library." The rendering library seems to be independent of FORTH. But the core language (sans library) seems like FORTH to me. -- JeffGrigg

The precise genealogical relationship appears to be mildly controversial, however, some things are crystal clear: There's more to say about Postscript (and Forth), but that's just off the top of my head (I've implemented interpreters for both languages). -- DougMerritt


One should note that PostScript isn't the first time a postfix language has been invented independently from Forth. The JoyLanguage came upon it from the FunctionalProgramming direction. Discovering many of the same stack operators (named differently) and adding other operators which make more sense in a functional language.


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