@Leo Ooh, nice. I need some really good examples of how to use Eval ~.
I need to make dynamic code using a string option and use the result of a previous stage as input to the evaluated code, which the guide says you can do.
I'm having trouble figuring out Eval just by guessing
Retina, 55 bytes
P`.+
G1`
C`
.+
$+2
Cv`..
.+
$+1
"L,$+5vs,$+3,`.+"^~`
$0
Try it online!
Based on this program that I created to transpose any size of rectangle, which uses Leo's suggestion for transposing a rectangle of a known size.
@mbomb007 That's nice! Now I don't have time to try it, but I think it could be golfed quite a bit by using $. substitutions instead of C stages to compute lenghts