there is another one:

path=arc(6,55,360);
newpath = path3d(path);

for(i=[0:4])
{
echo (i);
echo(newpath[i]);
translate(newpath[i]) cylinder(h=2,d=2);
}

On Thu, 18 Jul 2024 at 21:32, Sanjeev Prabhakar sprabhakar2006@gmail.com
wrote:

When saying that you are getting an error message, it is always good to report what error message you are getting. That said, I see a couple of clear problems.  Sanjeev seems to have found them, but didn’t really elaborate.

The first echo() has no semicolon after it.  Syntactically, that makes the second echo be its child.  To my mild surprise, that does work, but it’s still not a conventional structure.

The scope of the for() is the pair of echo() calls.  The translate() is outside its scope.  You want braces around all three.

The argument to the translate is the wrong type.  This one merits a bit more discussion.

translate() wants a vector (list) of two or three numbers.  Brackets make a list, so [1,2,3] is a list of three numbers.  BOSL2’s path stuff generates a list of such lists.  newpath[i] is such a list; in this case, a list of three numbers. So far so good.  But then you have brackets around it, so you are making a list of one element, with that one element being a list of three numbers.  That’s not what translate() wants. Lose the brackets.

I don’t know whether it applied here, but I think that something like this is a common error in new OpenSCAD users: thinking that brackets are part of the syntax of translate() and similar modules.  They aren’t.  translate() wants a list of three numbers, however constructed.  The argument can be an explicitly constructed list with [num1,num2,num3], or it can be a variable whose value is such a list, or it can be constructed some other way (function call, et cetera).  Brackets are only necessary and appropriate when you are explicitly creating the list right there.

BTW, a simplification:  while many languages require you to loop through the indexes of an array to retrieve the values in succession, OpenSCAD doesn’t.  “for (val = list) …” will execute the body once for each element in the list.  When you don’t need the index for some other purpose, avoiding it makes things simpler.

Net, your snippet above should probably look like:

for (p = newpath) {
echo(p);
translate(p) cylinder(h=2,d=2);
}

[ Sorry if this is a duplicate.  Not sure if the first went through. ]

When saying that you are getting an error message, it is always good to report what error message you are getting. That said, I see a couple of clear problems.  Sanjeev and Jon seem to have found them, but didn’t really elaborate.

The first echo() has no semicolon after it.  Syntactically, that makes the second echo be its child.  To my mild surprise, that does work, but it’s still not a conventional structure.

The scope of the for() is the pair of echo() calls.  The translate() is outside its scope.  You want braces around all three.

The argument to the translate is the wrong type.  This one merits a bit more discussion.

translate() wants a vector (list) of two or three numbers.  Brackets make a list, so [1,2,3] is a list of three numbers.  BOSL2’s path stuff generates a list of such lists.  newpath[i] is such a list; in this case, a list of three numbers. So far so good.  But then you have brackets around it, so you are making a list of one element, with that one element being a list of three numbers.  That’s not what translate() wants. Lose the brackets.

I don’t know whether it applied here, but I think that something like this is a common error in new OpenSCAD users: thinking that brackets are part of the syntax of translate() and similar modules.  They aren’t.  translate() wants a list of three numbers, however constructed.  The argument can be an explicitly constructed list with [num1,num2,num3], or it can be a variable whose value is such a list, or it can be constructed some other way (function call, et cetera).  Brackets are only necessary and appropriate when you are explicitly creating the list right there.

BTW, a simplification:  while many languages require you to loop through the indexes of an array to retrieve the values in succession, OpenSCAD doesn’t.  “for (val = list) …” will execute the body once for each element in the list.  When you don’t need the index for some other purpose, avoiding it makes things simpler.

Net, your snippet above should probably look like:

for (p = newpath) {
echo(p);
translate(p) cylinder(h=2,d=2);
}

Hi Jordan
thanks for this didactic wonderful explanation!!

BR Karl

Am 19.07.24 um 08:48 schrieb Jordan Brown: