Recursively constructing an object in OpenSCAD - recursion

Question

So I'm trying to build a simple stack of scaled cubes using a recursive function:
function stack(levels) = (
levels <= 0
? cube([1,1,1], center=true)
: union() {
cube([1,1,1], center=true);
translate([0, 0, 0.9]) scale([1, 1, 0.9]) stack(levels - 1);
}
);
stack(5);
Now for some reason I currently don't understand OpenSCAD tells me that I've got a syntax error in line 4, marking the editor like this:
Sadly the console only yields this output:
ERROR: Parser error in line 4: syntax error
ERROR: Compilation failed!
So it's somewhat hard for me to figure out what exactly I'm doing wrong.
I guess there's a way to do this using for, but I would consider a recursive approach more readable.
I'll try to do this with modules, and if that doesn't work I can resort to use for in combination with modules I suppose - it's more that I'd like this to work and find it very readable.
Update: So from the OpenSCAD User Manual I get this snippet:
I would tend to interpret this so that it is not possible to create a recursive structure the way I imagined.
Instead I could:
Use a helper function to generate the cube parameters and compute their union afterwards.
Rewrite the structure in terms of a for loop.
I'm uncertain whether my conviction is correct, but the reasoning is this:
I cannot create objects in a function because that would have an effect.
I cannot use a module recursively because it doesn't return a result and possibly the way variables work in OpenSCAD would interfere with the idea.

Answer 1

You can make a recursive module, the only problem there is the ternary operator takes values not objects:
module stack(levels) {
if(levels) {
cube([1,1,1], center=true);
translate([0, 0, 0.9]) scale([1, 1, 0.9]) stack(levels-1);
} else {
cube([1,1,1], center=true);
}
}
stack(5);
Here's another example: https://github.com/cashlo/OpenSCAN-Objects/blob/master/xmas-tree.scad