POV-Ray : Newsgroups : povray.pov4.discussion.general : Random POV-Ray 4 SDL proposal, #1 Server Time
28 Oct 2021 01:11:35 EDT (-0400)
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From: Saul Luizaga
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 9 Jun 2021 12:56:06
Message: <60c0f2a6$1@news.povray.org>
delete this message, I can't do it myself from Mozilla Thunderbird, 
tried to unsubscribe and subscribe several times, tried several methods, 
it was a moment of insanity, sorry


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From: Bald Eagle
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 9 Jun 2021 14:15:00
Message: <web.60c104b02ab8183e1f9dae3025979125@news.povray.org>
"Mr" <nomail@nomail> wrote:
> clipka <ano### [at] anonymousorg> wrote:

> > A simple POV-Ray scene described in this format might look like this:
> [...]
> >     {
> >       camera: {
> >          up: [ 0, 1, 0 ],


> The  first thing bothering me is the combination of colons and brace characters
> in some places or maybe rather that it seems it can't be used the same  way
> elsewhere?
> Would we have to write camera: {
> It would seem a little cluttered to have to use a : for just specifying the
> opening of a block. do we have to ?

I would say that some of these things will have to be looked at from the
perspective of
1. the developer / parser
2. the end user

I would like it if we could dispense with some of the brackets altogether, and
just have a LF/CR/NL or new keyword signal the end of a statement.
On the other hand, I _would_ like to have explicit endings for code blocks, such
as
#endcamera
#endif
#endfor
#endwhile

as I think that overall it would be in the long run easier from both
perspectives to follow and debug code.

> > One possible change to the syntax could be the use of regular braces
> > around list items instead of square brackets to specifically denote
> > vectors, if only to make it more pleasant to read.

There has been some discussion about typing and automatic vector promotion.
Getting rid of brackets and braces altogether would make a little less typing to
do, but maybe it would be worth it to lose that benefit if we had to specify
things like vec2, vec3, vec4 - if only to keep it at the forefront of our minds
what sort of values we're dealing with in any given instance.


> > I'd also love to add ranges to the set of types, using a syntax akin to
> > this:
> >
> >     [ 1 .. 20 ] // range from 1 to 20, both inclusive
> >     ( 1 .. 20 ) // range from 1 to 20, both exclusive
> >     [ 1 .. 20 ) // range from 1 inclusive to 20 exclusive
> >     ( 1 .. 20 ] // range from 1 exclusive to 20 inclusive

Ranges would be very nice, but maybe I would like to get rid of the parentheses
in favor of a leading keyword, so that we could instead have all manner of
parentheses available for use in grouping terms in equations without making
parsing (more of) a complicated ordeal.

so, the keywords for the above examples might be ii, ee, ie, ei.

then we could write equations like   val = [sin (x+3) / pi] + (tau/6) -
abs{cos[(q/360)+(<n/0.5>+0.5)]};
It would also be nice to drop the requirement for #declare and just write
     x=3;


> > symbols as (entirely optional) syntactic sugar.

This would be very nice, especially for placing the text/symbol in the render.

The same would go for a mechanism for exposing the text of a parsed line of code
to the SDL.
What I mean by that is to have a mechanism similar to that in a spreadsheet
whereby if cell A3 has (x+1)/10 in it, then formula (A3) returns the string
"(x+1)/10"


> But with the prerequisites that they should have an explicit
> alternative for when we don't know or have any internet to check for the code to
> type. most people never enter a unicode special number their whole life. but
> maybe the parsing times could really be worth that learning?

We could do that with an include file, like we have with functions.inc -
symbol.inc could have #declare sym_nabla = symbol (U+2207); or however it would
get coded.


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From: clipka
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 9 Jun 2021 20:30:31
Message: <60c15d27$1@news.povray.org>
Am 09.06.2021 um 20:13 schrieb Bald Eagle:

>>> I'd also love to add ranges to the set of types, using a syntax akin to
>>> this:
>>>
>>>      [ 1 .. 20 ] // range from 1 to 20, both inclusive
>>>      ( 1 .. 20 ) // range from 1 to 20, both exclusive
>>>      [ 1 .. 20 ) // range from 1 inclusive to 20 exclusive
>>>      ( 1 .. 20 ] // range from 1 exclusive to 20 inclusive
> 
> Ranges would be very nice, but maybe I would like to get rid of the parentheses
> in favor of a leading keyword, so that we could instead have all manner of
> parentheses available for use in grouping terms in equations without making
> parsing (more of) a complicated ordeal.
> 
> so, the keywords for the above examples might be ii, ee, ie, ei.
> 
> then we could write equations like   val = [sin (x+3) / pi] + (tau/6) -
> abs{cos[(q/360)+(<n/0.5>+0.5)]};
> It would also be nice to drop the requirement for #declare and just write
>       x=3;

I think we can have both.

The style of range notation is deliberately chosen to make it easy to 
determine what is the start of something and what the end; for instance, 
I personally prefer the following alternative notation because I find it 
more intuitive with respect to which end is "inclusive" and which is 
"exclusive", but _that_ would indeed seriously complicate parsing:

     [ 1 .. 20 ] // range from 1 to 20, both inclusive
     ] 1 .. 20 ] // range from 1 exclusive to 20 inclusive

As for the proposed syntax further above, distinguishing an arbitrary 
mathematical expression from a range should be easy: All the parser 
needs to do is look at the "..", which we can take as an operator that 
takes two numeric values and returns what we might call a "naked range". 
Parentheses and/or brackets around such a "naked range" would then 
convert that into what we might call a "qualified range". (Further 
wrapping a "qualified range" in more parentheses or brackets would have 
no additional effect.)

>> But with the prerequisites that they should have an explicit
>> alternative for when we don't know or have any internet to check for the code to
>> type. most people never enter a unicode special number their whole life. but
>> maybe the parsing times could really be worth that learning?
> 
> We could do that with an include file, like we have with functions.inc -
> symbol.inc could have #declare sym_nabla = symbol (U+2207); or however it would
> get coded.

Explicit ASCII alternatives, hard-baked into the language, would be a 
must, IMO. As I mentioned, Unicode symbols would be syntactic sugar. The 
ASCII constructs would be the real deal, while the Unicode symbols would 
be considered shortcuts.


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From: Mr
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 10 Jun 2021 07:20:00
Message: <web.60c1f5222ab8183e16086ed03f378f2@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:

> Explicit ASCII alternatives, hard-baked into the language, would be a
> must, IMO. As I mentioned, Unicode symbols would be syntactic sugar. The
> ASCII constructs would be the real deal, while the Unicode symbols would
> be considered shortcuts.

Okay, and do you confirm that such kind of things would have significant impact
on parse time, like: linearly, if you divide the character amounts by two you
get half parsing code?


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From: clipka
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 10 Jun 2021 10:25:13
Message: <60c220c9@news.povray.org>
Am 10.06.2021 um 13:18 schrieb Mr:
> clipka <ano### [at] anonymousorg> wrote:
> 
>> Explicit ASCII alternatives, hard-baked into the language, would be a
>> must, IMO. As I mentioned, Unicode symbols would be syntactic sugar. The
>> ASCII constructs would be the real deal, while the Unicode symbols would
>> be considered shortcuts.
> 
> Okay, and do you confirm that such kind of things would have significant impact
> on parse time, like: linearly, if you divide the character amounts by two you
> get half parsing code?

No, parser performance is not that simple.

A good parser (which POV-Ray's old one is not by any stretch, and even 
the overhauled one is only a step on the way there) will just _scan_ the 
whole file once (i.e. identify start and end of each character sequence 
that look like a token at first glance - e.g. sequences that look like 
numbers, sequences that look like keywords or identifies, sequences that 
look like operands, etc.), _tokenize_ it once (i.e. translate those 
character sequences into internal numeric IDs, aka tokens), and from 
there on just juggle those IDs.

The next steps would be to either...

- walk through those tokens and "execute" them, implementing loops by 
processing the corresponding tokens over and over again; in this case 
processing the loops again and again would be the bottleneck.

- digest that token sequence even further, "compiling" it into something 
that can be executed so efficiently that it might have a chance to 
become negligibe compared to the time spent scanning and tokenizing; but 
to achieve that, the effort to bring it into this efficient form will 
itself outweigh the effort of scanning and tokenizing.

In either case, the genuinely time-consuming portions of parsing will 
work on a representation in which the number of characters comprising 
the keywords or operands will have become entirely irrelevant.


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From: Mr
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 12 Jul 2021 09:05:00
Message: <web.60ec3d1b2ab8183e16086ed03f378f2@news.povray.org>
Bump! (unless discussion is going on elsewhere, if so, sorry for missing it) and
not knowing much about json yet, I have a remark / question to the experts.

I also like the idea to use end of lines for ending some statements. To me that
is one cause for the popularity of python, staying as close to pseudo code as
possible in the core functionality. (which doesn't prevent to use stuff like
brackets for list comprehensions or more recently type annotations, depending on
the scope of the snippet or project written. There's even some days when you
forget the colon after concentrating on formulation of an if clause, and you
think; couldn't we do without it?

However , I have to assume that some of the syntax previously mentionned is
organically intertwined within JSON core syntax... But I do not have the
experience to distinguish which at all.


So my question to the experts is, could end of line statement still be
compatible with the proposed json paradigm / standard ? maybe in the worse case,
breaking away from the standard but by chosing a subset of it... or whatever
shift...?

(I only asked because it would seem that we would be at leat two in favour of
such a feature, but I for one would gladly give the request up after being
explained a reason, such as performance gain etc...)


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From: clipka
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 12 Jul 2021 10:54:35
Message: <60ec57ab$1@news.povray.org>
Am 12.07.2021 um 15:01 schrieb Mr:

> So my question to the experts is, could end of line statement still be
> compatible with the proposed json paradigm / standard ? maybe in the worse case,
> breaking away from the standard but by chosing a subset of it... or whatever
> shift...?

One of the key features of the proposed language would be that any valid 
JSON file would automatically qualify as valid POV-Ray SDL file 
(provided the "document object model", aka "schema", matches, i.e. the 
hierarchy of how and what stuff is nested where).

Allowing for line endings to terminate statements might break that 
compatibility, because the JSON standard allows line endings anywhere it 
allows for whitespace.


I used JSON as a starting point for the proposed SDL format not only to 
start _somewhere_ but specifically because being 100% compatible with 
JSON would have the advantage that there are tools and libraries galore 
out there to generate that format.

JSON is one of just a handful of probably the top most popular formats 
for storage and exhange of structured data:

- XML
- JSON
- YAML

XML is painfully verbose, and therefore not an option. YAML is very 
concise, but assigns semantics not only to line endings but also to 
indentation, and that is something I'm anything but a fan of.

Which leaves us with JSON as the next most obvious choice - which 
happens to be similar to POV-Ray's current SDL both in terms of 
verbosity and overall look & feel (thanks to both ultimately being 
inspired by C).


Also, categorically making any line ending end a statement has the big 
drawback that any statement must be written on a single line. To work 
around this, the statement-ending semantics of line endings would have 
to be weakened depending on context, which in turn would add more 
complexity to the parser, and moreover to the language itself, 
potentially making it difficult for users to grasp how the line-ending 
rules work.

An alternative would be to make some of the commas optional, but at 
least as soon as we add certain of our own features we'd run into 
similar problems to avoid ambiguities.


> (I only asked because it would seem that we would be at leat two in favour of
> such a feature, but I for one would gladly give the request up after being
> explained a reason, such as performance gain etc...)

Compatibility with the base format, keeping the format free from 
ambigiuties, and keeping the format reasonably easy for users to grasp. 
That's pretty much all the reason there is to not assign special 
semantics to line endings.

In terms of performance, it probably wouldn't make much of a difference.


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From: Mr
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 13 Jul 2021 06:10:00
Message: <web.60ed654f2ab8183e16086ed03f378f2@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Am 12.07.2021 um 15:01 schrieb Mr:
>
> > So my question to the experts is, could end of line statement still be
> > compatible with the proposed json paradigm / standard ? maybe in the worse case,
> > breaking away from the standard but by chosing a subset of it... or whatever
> > shift...?
>
> One of the key features of the proposed language would be that any valid
> JSON file would automatically qualify as valid POV-Ray SDL file
> (provided the "document object model", aka "schema", matches, i.e. the
> hierarchy of how and what stuff is nested where).
>
> Allowing for line endings to terminate statements might break that
> compatibility, because the JSON standard allows line endings anywhere it
> allows for whitespace.
>
>
> I used JSON as a starting point for the proposed SDL format not only to
> start _somewhere_ but specifically because being 100% compatible with
> JSON would have the advantage that there are tools and libraries galore
> out there to generate that format.
>
> JSON is one of just a handful of probably the top most popular formats
> for storage and exhange of structured data:
>
> - XML
> - JSON
> - YAML
>
> XML is painfully verbose, and therefore not an option. YAML is very
> concise, but assigns semantics not only to line endings but also to
> indentation, and that is something I'm anything but a fan of.
[...]

Thanks a lot for this answer clarifying the stakes, Now I'll feel more at peace
when POV4 will keep its tolerant and meaningless line endings behaviour .

I would also hate it to be like xml compared to the other two options. So I
looked here https://levelup.gitconnected.com/json-vs-yaml-6aa0243aefc6


Coming from Python I know that my apriori not (yet) feeling the same about this
is probably thus biased, but could you please also develop more about why as a
user you would prefer an abundant punctuation over a meaningful indentation
system ?


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From: clipka
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 13 Jul 2021 10:46:35
Message: <60eda74b@news.povray.org>
Am 13.07.2021 um 12:05 schrieb Mr:

> Coming from Python I know that my apriori not (yet) feeling the same about this
> is probably thus biased, but could you please also develop more about why as a
> user you would prefer an abundant punctuation over a meaningful indentation
> system ?

Indentation is trouble.

If you ever encounter a source file that mixes tab-indented and 
space-indented code, you may realize what I mean. In languages that 
don't assign semantics to indentation, such a mix results in eyesores at 
worst. In languages where whitespace matters, it can get far worse.

The core problem there of course is that there are different standards 
how many spaces a tab should be worth: Two? Four? Eight? Three? Six? 
Five? Been there, seen all of those.

And it's not like you can tell at a single glance what's going wrong 
there, with tabs and spaces both being entirely invisible and therefore 
looking identical.


And if you've ever edited makefiles (or proto-makefiles as used in 
Autoconf-based build systems), you really learn to hate languages that 
assign semantics to whitespace. If you set your editor to replace tabs 
with spaces, you _will_ break your makefiles.

(Granted, most indentation-aware languages don't assign different 
semantics to tab indentation vs. space indentation.)


So there's the tab issue, for starters.


The next issue of indentation-structured languages - or at least those 
that use a hard "end of line is end of statement" rule - is that they 
put a practical limit on how complex you can make a single statement. If 
you have a very complex mathematical formula, you need to break it up 
into smaller chunks, assign those to variables, and then assemble those 
into your final result. Or even more interim results first.

Now it can be argued that this forces you to give more structure to your 
code, thus making it easier to understand.

However, breaking up an expression into named sub-expressions is not the 
only way to structure complex formula. Specifically, even short formulae 
might benefit from being spread out over multiple lines. And maybe 
liberally peppered with indentation without having to worry about 
breaking semantics.

And what if you're just using a formula from someplace else, and have no 
idea whatsoever what the individual portions of the formula really mean? 
Or if you've optimized a mathematical expression for performance in such 
a way that its original "natural structure" is no longer visible anyway?

What you'll then do is use meaningless single-letter variable names to 
the sub-expression, and the resulting code will look far more complex 
and far more difficult to grasp than it would have, could you have 
written it as a single expression spread over multiple lines and 
indented freely.

And speaking of variable names, restricting the practical length of a 
statement may actually lead to poorer rather than better code, in that 
people may develop a habit of keeping variable names short and thus 
potentially more cryptic.

(Some "end-of-line-aware" programming languages allow spreading 
statements across multiple line by "invalidating" a line ending, but the 
corresponding syntax tends to be somewhat clunky. If you've ever done 
much C/C++ preprocessor programming, you'll know what I mean. What's 
more, such syntax often breaks in the presence of stray blanks at the 
end of a line, which are a pain to find.)


Also, sometimes it may actually improve readability to put multiple 
short statements on a single line (especially when there's a group of 
statements that repeats in structure). Some end-of-line-aware languages 
allow this (e.g. shell scripts), but again generally at the cost of 
added symbols and therefore clunkiness.

Of course it can be argued that whitespace-agnostic languages need the 
same extra symbols between statements, not only in a single line but 
also between lines. But in my mind separator characters become less 
clunky if they're used consistently throughout, as opposed to just on 
special occasions.


And then there's the matter of copy-and-pasting:

When you copy-and-paste code from arbitrary sources (a web page here, a 
PDF there, a terminal window over there, and what else you might happen 
to come across), you may end up with broken indentation.

If the code is reasonably complex, have fun faithfully restoring the 
original semantics.

If the semantics is all in the non-whitespace, smart editors may 
actually be able to restore the original indentation, at least to the 
point that its structure is agion easy enough to grasp for a human. If 
semantics is in the indentation itself, how could an editor ever restore 
that indentation?


Also, look at written human language: There's a reason we're using 
special characters to indicate the boundaries between sentences and 
subclauses, rather than using a "one line = one sentence" default rule 
and using special syntax to spread sentences across multiple lines.


Now I can't rule out that Python may for some reason manage to get 
around each and every one of the above issues - I've had virtually no 
exposure to that language yet. But based on my experience with other 
end-of-line- and indentation-aware languages, my guess is that at least 
some of those issues do apply.

But even if Python should be entirely immune, that doesn't mean it would 
be easy to design a new POV-Ray SDL that is also indentation-aware and 
has the same level of immunity as Python.

And yet, feel free to throw together a corresponding proposal, and 
present it here. Even if it should turn out to be seriously flawed, 
there may still be interesting and inspiring morsels in there.


Heck, I've never claimed that my own proposal was really any good. I 
just threw it out there to have _some_ starting point. For discussion at 
worst, or for further development at best.

As a matter of fact, I don't even _particularly_ like it. It's not very 
elegant, because it is not custom-tailored to our needs. It is derived 
from an existing base. It does have interesting properties though, one 
of which arises _specifically_ out of being derived from an existing 
base. And for now I think it has the potential to be useful, and maybe 
even reasonably good.

No worse than the current SDL, and better structured - that's all I'm 
asking of a new SDL. Ideally with consistent syntax between scene 
descriptions and functions, and maybe with a rigorous enough structure 
to allow for a compiling rather than interpreting parser.


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From: jr
Subject: Re: Random POV-Ray 4 SDL proposal, #1
Date: 14 Jul 2021 05:40:00
Message: <web.60eeafce2ab8183e5e0fed26cde94f1@news.povray.org>
hi,

clipka <ano### [at] anonymousorg> wrote:
> ...
> No worse than the current SDL, and better structured - that's all I'm
> asking of a new SDL. Ideally with consistent syntax between scene
> descriptions and functions, and maybe with a rigorous enough structure
> to allow for a compiling rather than interpreting parser.

have you looked at Tcl/Tk yet, for inspiration?  has many (imo) natty features,
nice, clean syntax, and byte-compiles.


regards, jr.


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