Discussion:
[OpenSCAD] Using children with let
John Savage
2018-09-12 14:06:41 UTC
Permalink
I would like to be able to write a single let() statement and use it on
multiple modules. A simple example is



module leta(){

let(a=23)

children();

}



leta() cylinder(h=a, d=a); // Doesn't work, a is unknown here.



However this does work:



module move(x){

translate([x,0,0])

children();

}



module cone_rod(){

cylinder(h=10,d=5);

cylinder(h=5,d1=15,d2=0);

}



move(0) cone_rod(); // Works as expected

move(20) cone_rod(); // Works as expected



What's the difference and why doesn't the first example work?



Thanks,

John
nop head
2018-09-12 15:05:18 UTC
Permalink
OpenSCAD variables have lexical scope by default, so they can only be seen
in the block they are defined in. So you could do children(a) to access the
23rd child but a is not visible outside leta() and more specifically only
under the let().

However, if you use $a it will have dynamic scope and be accessible in all
the modules and functions called from the block it is defined in.
Post by John Savage
I would like to be able to write a single let() statement and use it on
multiple modules. A simple example is
module leta(){
let(a=23)
children();
}
leta() cylinder(h=a, d=a); // Doesn't work, a is unknown here.
module move(x){
translate([x,0,0])
children();
}
module cone_rod(){
cylinder(h=10,d=5);
cylinder(h=5,d1=15,d2=0);
}
move(0) cone_rod(); // Works as expected
move(20) cone_rod(); // Works as expected
What’s the difference and why doesn’t the first example work?
Thanks,
John
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John Savage
2018-09-12 17:30:41 UTC
Permalink
Hi Nop Head(?) Thanks for your reply. I get it now. John



From: nop head [mailto:***@gmail.com]
Sent: 12 Sep 2018 04:05
To: ***@jegsav.com; OpenSCAD general discussion
Subject: Re: [OpenSCAD] Using children with let



OpenSCAD variables have lexical scope by default, so they can only be seen in the block they are defined in. So you could do children(a) to access the 23rd child but a is not visible outside leta() and more specifically only under the let().

However, if you use $a it will have dynamic scope and be accessible in all the modules and functions called from the block it is defined in.



On 12 September 2018 at 15:06, John Savage <***@jegsav.com> wrote:

I would like to be able to write a single let() statement and use it on multiple modules. A simple example is



module leta(){

let(a=23)

children();

}



leta() cylinder(h=a, d=a); // Doesn't work, a is unknown here.



However this does work:



module move(x){

translate([x,0,0])

children();

}



module cone_rod(){

cylinder(h=10,d=5);

cylinder(h=5,d1=15,d2=0);

}



move(0) cone_rod(); // Works as expected

move(20) cone_rod(); // Works as expected



What’s the difference and why doesn’t the first example work?

Thanks,

John

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