This one is a beginners thing for sure but after 4 hours head scratching...
Consider this simple loop that produces 4 values per loop

p = concat([1],[for (i=[1:4:9]) [i+1,i+2,i+3,i+4]]);
echo(p);

ECHO: [1, [2, 3, 4, 5], [6, 7, 8, 9], [10, 11, 12, 13]]

However, what I want is a flat list like:

ECHO: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]

I managed this weird contraption but that looses the "1" at the start

echo([for (i=[0:1:len(p)-1], j=[0:1:len(p[i])-1]) p[i][j]]);
ECHO: [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]

How do I do this?

--
Sent from: http://forum.openscad.org/

And of course I find a solution immediately after I posted.

function flatten(a)=
[ for(x=a)
for(b=len(x)==undef? x:flatten(x)
)
b ];

But if there is any info that helps me to manage my lists better, I love to
hear.

--
Sent from: http://forum.openscad.org/