refactor

src/util/_impl/_shuffle_impl.scad

@@ -0,0 +1,4 @@
+use <../swap.scad>;
+
+function _shuffle(lt, indices, leng, i = 0) =
+    i == leng ? lt : _shuffle(swap(lt, i, indices[i]), indices, leng, i + 1);

src/util/shuffle.scad

@@ -1,4 +1,14 @@
-use <swap.scad>;
+/**
+* shuffle.scad
+*
+* @copyright Justin Lin, 2021
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib3x-shuffle.html
+*
+**/ 
+
+use <_impl/_shuffle_impl.scad>;
 
 function shuffle(lt, seed) = 
     let(
@@ -6,6 +16,3 @@ function shuffle(lt, seed) =
         indices = [for(i = is_undef(seed) ? rands(0, leng, leng) : rands(0, leng, leng, seed)) floor(i)]
     )
     _shuffle(lt, indices, leng);
-
-function _shuffle(lt, indices, leng, i = 0) =
-    i == leng ? lt : _shuffle(swap(lt, i, indices[i]), indices, leng, i + 1);