Stack-Oriented Programming

Re:Stack-Oriented Programming by munk-a on Tuesday January 14, 2020 @04:35PM (#22049475)

That's quite helpful, it may be a lack of in-depth reading of the page but the persistence and implicit passing of computation between operations is helpful to understand the differentiation. In more classic procedural languages you'll usually have a function stack that is being pushed and popped two but actual program values are handled using entirely arbitrarily loaded references that get juggled around as needed for computation - does stack programming often have a similar concept to frame popping when an issue with I/O or something similar is encountered or do we just get a panic that aborts computation?

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Re:Stack-Oriented Programming by triska on Tuesday January 14, 2020 @04:45PM (#22049558)

To get a glimpse of stack-oriented programming, I really like and recommend PostScript, because this also automatically introduces you to a widely used programming language with important practical applications, and it's also great fun to learn.

So, for instance, let's elicit an error using Ghostscript, a freely available and efficient PostScript interpreter:

    $ gs
    GPL Ghostscript 9.27 (2019-04-04)
    ...

At the "GS>" prompt, I now define "f" via:

    /f { /hello g } def

Note that "f" refers to "g", which is not yet defined.

Therefore, when I then invoke "f" via:

    GS>f

I get an error:

    Error: /undefined in g

And importantly, the stack is retained, so I can inspect it at this point, interactively, using for example "pstack":

    GS<1>pstack
    /hello

This shows that /hello is still on the stack. From there, we can resume in various ways, for example by clearing the stack (with "clear"), by redefining and reinvoking "f" etc.

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Re:Stack-Oriented Programming by haolez on Tuesday January 14, 2020 @07:13PM (#22050579)

Is PostScript used beyond page description? I'm really curious :)

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Re:Stack-Oriented Programming by pedrow on Wednesday January 15, 2020 @04:55AM (#22053000)

I recently saw an announcement[0] of a Z-machine in Postscript. The Z-machine is a runtime for text adventure games. Also posted on HN[1] but no comments were made.

[0]: https://groups.google.com/d/msg/rec.arts.int-fiction/HNtntxC...

[1]: https://news.ycombinator.com/item?id=21367412

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Re:Stack-Oriented Programming by zzo38computer on Wednesday January 15, 2020 @04:47PM (#22059093)

Yes; I wrote that program, and the Usenet message and the message on HN (which mentions the message ID for the Usenet message). If you have comments about it, I suggest writing a follow-up message on Usenet.

PostScript is a real programming language and can be used for many things (especially graphics). I also wrote a JSON parser in PostScript (see message <[email protected]> on comp.lang.postscript), and then someone else post their JSON parser in PostScript too.

I think PostScript isn't such a good protocol or document format, but it is good as a programming language. It is what I might use if I want to make a diagram (but unfortunately Ghostscript cannot produce SVG output; it can output PDF though, as well as many raster formats).

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Re:Stack-Oriented Programming by haolez on Thursday January 16, 2020 @07:59PM (#22070805)

Nice! Thanks for answering! Would you choose PostScript over Forth as a general purpose language?

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Re:Stack-Oriented Programming by zzo38computer on Thursday January 16, 2020 @10:06PM (#22071493)

I think it would depend on what I am trying to make; there are advantages and disadvantages to each. In the case of the JSON parser, I think it is helpful that PostScript has data structures (such as arrays and dictionaries) and arbitrarily typed values like JavaScript and many other scripting languages have. In the case of Z-machine, Forth would probably do as well as PostScript (or probably Forth would do better, actually).

Someone was unsure how useful would be the JSON parser I wrote in PostScript, but if you want to print some diagram based on data in JSON format, then it can be helpful.

(I could implement Z-machine in Forth too if I wanted to do, but I have not done so yet because I have other things to do; I don't know if I might do so in future or not. I could implement Z-machine in any programming language with byte arrays, including assembly language (I started but haven't finished one in 6502).)

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Re:Stack-Oriented Programming by PeCaN on Tuesday January 14, 2020 @08:42PM (#22051040)

Sun made a windowing system based on (Display) PostScript way back https://en.wikipedia.org/wiki/NeWS

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Re:Stack-Oriented Programming by rwmj on Wednesday January 15, 2020 @05:02AM (#22053032)

https://www-cdf.fnal.gov/offline/PostScript/fractal-fern.ps

is a fractal fern. This is page description, but not in the normal way that it's used. Compare the output in a PS or PDF viewer with the source code which is under 1.5K.

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Re:Stack-Oriented Programming by RodgerTheGreat on Tuesday January 14, 2020 @10:08PM (#22051458)

Once I wrote a bingo card in PostScript which would randomize its cells every time you printed it. That's almost useful.

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Re:Stack-Oriented Programming by kortex on Tuesday January 14, 2020 @10:44PM (#22051603)

I found a .ps that generates timing wheel patterns (discs with alternating black and white radial bands). you'd plug in inner/outer radius, number of bands, and you'd get a printable document from that file. As in, the .ps file was code, which printed as an image. I now know this is the origin of pdf but it blew my mind.

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Re:Stack-Oriented Programming by hnick on Tuesday January 14, 2020 @08:59PM (#22051132)

It's Turing-complete, which makes writing programs to analyse documents a bit of a problem at times.

But I think maybe you meant in the sense of "in the real world", and I can't think of any examples. Prefixing some postscript to a document to manipulate that file is something it can be suited for, rather than using an external language to do so.

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Re:Stack-Oriented Programming by Mikhail_Edoshin on Thursday January 16, 2020 @08:12AM (#22064133)

Even in page description alone the programming capabilities are rather useful. E.g. to produce barcodes you can just generate them from data.

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Re:Stack-Oriented Programming by narag on Tuesday January 14, 2020 @08:16PM (#22050911)

There's an old language, pop11, that's similar to lisp but stack oriented. A few sections of the manual will show you the kind of stack tricks that make different order useful:

https://www.cs.bham.ac.uk/research/projects/poplog/primer/#s...

Functions that return several results, implicit parameters, open stack, etc. It's a lot of fun.

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