[OpenSCAD] OpenSCAD and data flow languages

doug moen doug at moens.org
Tue Oct 4 17:50:13 EDT 2016

Thanks for the detailed response, Richard. Some good ideas to think about.

On 4 October 2016 at 06:17, Richard Urwin <soronlin+openscad at googlemail.com>

> I don't know anything about how OpenSCAD works internally, but it seems to
> me
> that you need to generate a tree of objects to be created. A functional
> programming language can be represented as such a tree and is therefore a
> good fit to your needs. However you have other needs that are not well
> represented by the functional model. For example is in not required that a
> functional program is parallelizable but such would be of great use to
> OpenSCAD with its extended execution time and the prelevence of
> multiple-processor architectures. Language structures that OpenSCAD needs
> such as the union and difference constructs with their code bodies bend the
> functional paradigm. (They are special case lambda expressions but the user
> cannot create such things.) OpenSCAD's dependence on recursion to support
> certain programming needs creates a barrier to entry for newbies and an
> optimization issue for developers. Other functional languages either
> provide
> structures that bend the functional paradigm or put major effort into
> optimization. Neither of which approaches solve both of the issues that
> OpenSCAD has.
> A Data Flow language represents its program as a directed graph of
> operations. The nodes represent operations and the edges between nodes
> represent variables.
> <http://forum.openscad.org/file/n18526/graph.png>
> The graph on the left represents the program:
> A = 2;
> B = 3;
> C = 5;
> D = 1.2;
> cylinder(r=A+B, h=C*D);
> When a node has all the inputs it needs it is free to execute. So the
> values
> 2 and 3 flow to the "+" node which then executes and passes the "radius"
> value to the "cylinder" node. Simultaneously, the "*" node receives its
> inputs and also executes, passing the result to the "cylinder" node as its
> "height" argument. The "cylinder" node now has all of its data and can
> execute in its turn.
> A data-flow program is inherently parallelizable on common-memory
> multi-processor architectures; the graph can be partitioned easily. But to
> maintain that flexibility it has precisely the same requirement that
> OpenSCAD has that variables don't change etc.
> The graph on the right is for the example in the OpenSCAD README:
> union() {
>   cylinder(h = 30, r = 8);
>   translate([0, 0, 40]) sphere(20);
> }
> I imagine that this is identical to the tree that OpenSCAD produces for the
> same code, maybe with more nodes and you may be more used to seeing it
> upside-down. The Data Flow representation is precisely the same as the tree
> form that OpenSCAD requires. Even if their execution dynamics are
> different,
> their needs coincide. Which is why I said that "OpenSCAD is to all
> *external* purposes a Data Flow language".
> SISAL offers a richer programming environment than OpenSCAD. It has
> aggregate data types and more powerful array handling in addition to its
> for
> loops which provide an alternative to recursion in most cases. It is an old
> language with an out-dated syntax however it has solved many of the issues
> that OpenSCAD has still to address. An investigation into its source code
> may benefit OpenSCAD. (There's a modern implementation on SourceForge.)
> In addition, the redefinition of OpenSCAD as a data flow language could
> clean up its syntax in other ways, such as the removal of unnecessary
> parentheses on union, difference and for statements. Adopting SISAL's
> approach of everything being an expression rather than everything being a
> function would allow clearer syntax such as an if statement rather than the
> ?: trinary. The somewhat odd structures in OpenSCAD where a function
> invocation (such as union) has a code body would make sense. Such changes
> could easily be made backwards compatible.
> In summary, a data-flow paradigm fits OpenSCAD's requirements better than a
> functional model does and there are resources out there that would benefit
> the OpenSCAD project.
> --
> View this message in context: http://forum.openscad.org/
> OpenSCAD-and-data-flow-languages-tp18521p18526.html
> Sent from the OpenSCAD mailing list archive at Nabble.com.
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