See SmalltalkLanguage and ForthLanguage.
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My first exposure to Smalltalk was around 1985, when I read an article about Neon.  NeonLanguage was a Forth which contained a simple class facility.  I think Neon was one of the first ''real'' programming environments for the Mac.  It was most certainly the first Object Oriented language for the Mac.

I couldn't afford a Mac, but I got interested in getting an object oriented programming environment for my Atari ST.  I bought a copy of the Smalltalk-80 Blue Book and had visions of implementing Smalltalk in Forth.  I gave it a shot. I failed miserably.

The article on Neon (which appeared in the Forth Interest Group Journal) gave some detail on how you would go about extending Forth to become object oriented.  I had some success applying those techniques to my Atari ST Forth.

Ah, nostalgia...

-- ToddCoram (inspired by ForthInSmalltalk)
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OwenDensmore, refugee from Apple and then at Sun, and TomStambaugh spent an afternoon by the pool at the HyattPaloAlto in 86 or thereabouts, where we determined that a stack of dictionaries in PostScript (a print-oriented Forth extension) had the same semantics as an inheritance tree in Smalltalk. Owen was building NeWS (NetworkExtensibleWindowSystem, at that time it was called Sun Extended X), in Sun's homebrewed DisplayPostscript and elaborated those ideas into a reasonably full-featured display server, all extensible, all object oriented, and all in PostScript/Forth.

--TomStambaugh
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EdKleban and I coded up a Smalltalk-like framework in Forth we called OOGLE back in 1979/1980.  It ran in Forth on our IBM - Series1 and drove a graphic display based on a souped-up TI9900.  Yah, we had to do all sorts of stuff to get objects to "drag" such as outlining.  It was my curious introduction to OO.  Certainly a neat hack to demo graphics hardware at Siggraph.  

--KirkKitchen

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In 1986-87 I worked for a now defunct company, Synaptec, in Vancouver, B.C., Canada, that was working on a variant of Smalltalk based upon its own version of Forth, an Object Oriented Forth. Ahead of its time in many ways, this system, known as Audition, had quite a bit of development performed on it. Development continued for many years in various forms. In the period that I worked with them we solved over 600 bugs, 200 of which would leave the system crashed. We solved all but a few of those most serious bugs. The system was never completed and isn't available today due to legal problems with its ownership. It had an interactive environment that was inspired by Smalltalk. It also was aiming for some of the features of HyperCard. All in all a very interesting system.

?- PeterWilliamLount
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CategoryForth CategorySmalltalk