On 3/20/2021 3:32 PM, Torsten Paul wrote:

OpenSCAD is in a strange middle ground.

In one way, it's very dynamic.  It has no declarations and no
user-defined types.  It doesn't really have a way to say "this is what
an XXX structure looks like", outside the context of building a specific
instance of such a structure.

In another way, it's very static.  Values, once created, do not change. 
If you create a particular object/dictionary/structure with a particular
set of elements, that's exactly the set of elements and the set of
values that it will have for its entire life; you cannot add to it.

So far, it seems like those two combine to suggest that there's only one
abstraction needed - much as there's only one such abstraction in
JavaScript.

Curv just has the one concept, which I call "records". You can use them for lots of different things. A record describes a set of named model parameters (which can be passed around as arguments to functions and modules). You can roll your own object-oriented programming by storing function values in record fields, and I use this idea a lot. OpenSCAD is a simple language; I don't think anything more complicated is needed.

So here's a design loosely based on Curv.

r = {a: 1, b: [0,0], c: "hello"} is a record value.

A field name can also be specified as a string literal, eg,
{"a": 1, "b": 2}
This is used if the field name contains special characters.

r.a or r["a"] selects field "a" and returns 1.

A record value is printed as a record literal.

That's all you need to get started.

Curv has a more sophisticated design, which I will partially describe.

{a: 1, b: 2, each r}
'each r' includes the record 'r' into the record under construction in the above example.
This has left-to-right override semantics.
If 'r' defines a field name 'a', then that overrides the earlier definition 'a: 1'.
So in this example, 'a: 1' acts as the default value of 'a' if not specified by 'r'.

In some contexts, a record behaves like a list of ["name",value] pairs.
This allows for dynamic construction and introspection of records.

• within a record literal, 'each fieldlist' requires the list argument to contain ["name", value] pairs, which are converted to record fields.
• within a list literal, 'each record' converts the record to a list of ["name",value] pairs.

With these extensions, here is a 'fields' function that converts a record to a list of field names.
function fields(r) = [for (f = [each r]) f[0]];
Now fields({a:1,b:2}) returns ["a","b"].

Even with the extensions, that's a fairly simple design that is quite powerful.

Doug Moen.

On Sat, Mar 20, 2021, at 6:41 PM, Jordan Brown wrote:

and objects/structs. The obvious difference is that the
dictionaries are much more limited but allow access via a
dynamically produced key where objects usually only allow
statically defined names for access (needing some kind of
runtime reflection to make it dynamic).

Am 20.03.21 um 23:41 schrieb Jordan Brown:

Lua too has only a single, simple and very powerful abstraction: tables, which are implemented so that they can act as lists, dicts and structs.
Please see http://www.lua.org/pil/2.5.html

Honestly, I'm a bit surprised by the vehemence to reinvent the wheel in OpenSCAD while at the same time claiming it is a waste of time to even consider alternatives. Lua is complete, very well thought out, proven and made for embedding in projects like OpenSCAD: If time is expensive, it would be way more effective to spend it with integrating Lua rather than adding features to a language that will remain hard-to-use even with a dozen more features implemented.

Best regards,
Carsten

Am 22.03.21 um 22:18 schrieb William F. Adams via Discuss:

This seems to be as dead as most other related projects. I guess projects need active developers and a vivid community to thrive.

https://github.com/CadQuery/cadquery looks very interesting though! Installation is still a bit difficult, but they're working on improving that.

Best regards,
Carsten

Carsten Fuchs wrote:

Am 22.03.21 um 22:18 schrieb William F. Adams via Discuss:

That's a shame, yes, a program needs users.

With a bit of help I managed to get that installed, and agree it's one of the most promising of alternatives.
Things I miss in using it:
 - BlockSCAD - easy solutions found w/ a 'net search
William