use [each lt, v] to replace concat(lt, [v])

src/__comm__/__lines_from.scad

@@ -1,10 +1,7 @@
 function __lines_from(pts, closed = false) = 
     let(
         leng = len(pts),
-        endi = leng - 1
+        endi = leng - 1,
+        lines = [for(i = 0; i < endi; i = i + 1) [pts[i], pts[i + 1]]]
     )
-    concat(
+    closed ? [each lines, [pts[endi], pts[0]]] : lines;
-        [for(i = 0; i < endi; i = i + 1) [pts[i], pts[i + 1]]], 
-        closed ? [[pts[len(pts) - 1], pts[0]]] : []
-    );
-    

src/__comm__/__pie_for_rounding.scad

@@ -2,17 +2,11 @@ function __pie_for_rounding(r, begin_a, end_a, frags) =
     let(
         sector_angle = end_a - begin_a,
         step_a = sector_angle / frags,
-        is_integer = frags % 1 == 0
+        is_integer = frags % 1 == 0,
+        pie = [
+            for(ang = begin_a; ang <= end_a; ang = ang + step_a)
+                [r * cos(ang), r * sin(ang)]
+        ]
     )
-    r < 0.00005 ? [[0, 0]] : concat([
+    r < 0.00005 ? [[0, 0]] : 
-        for(ang = begin_a; ang <= end_a; ang = ang + step_a)
+    is_integer ? pie : [each pie, [r * cos(end_a), r * sin(end_a)]];
-            [
-                r * cos(ang), 
-                r * sin(ang)
-            ]
-    ], 
-    is_integer ? [] : [[
-            r * cos(end_a), 
-            r * sin(end_a)
-        ]]
-    );

src/__comm__/_convex_hull2.scad

@@ -11,7 +11,7 @@ function _convex_hull_sort_by_xy(lt) =
             before = [for(j = 1; j < leng; j = j + 1) if(_convex_hull_lt_than_by_xy(lt[j], pivot)) lt[j]],
             after =  [for(j = 1; j < leng; j = j + 1) if(!_convex_hull_lt_than_by_xy(lt[j], pivot)) lt[j]]
         )
-        concat(_convex_hull_sort_by_xy(before), [pivot], _convex_hull_sort_by_xy(after));
+        [each _convex_hull_sort_by_xy(before), pivot, each _convex_hull_sort_by_xy(after)];
 
 // oa->ob ct_clk : greater than 0
 function _convex_hull_impl_dir(o, a, b) =
@@ -28,7 +28,7 @@ function _convex_hull_lower_chain(points, leng, chain, m, i) =
         _convex_hull_lower_chain(
             points,
             leng,
-            concat(slice(chain, 0, current_m), [points[i]]),
+            [each slice(chain, 0, current_m), points[i]],
             current_m + 1,
             i + 1
         );
@@ -44,7 +44,7 @@ function _convex_hull_upper_chain(points, chain, m, t, i) =
         )
         _convex_hull_upper_chain(
             points,
-            concat(slice(chain, 0, current_m), [points[i]]),
+            [each slice(chain, 0, current_m), points[i]],
             current_m + 1,
             t,
             i - 1

src/__comm__/_convex_hull3.scad

@@ -13,7 +13,7 @@ function _convex_hull_sort_by_xyz(pts) =
             before = [for(j = 1; j < leng; j = j + 1) if(_cmp(pts[j], pivot)) pts[j]],
             after =  [for(j = 1; j < leng; j = j + 1) if(!_cmp(pts[j], pivot)) pts[j]]
         )
-        concat(_convex_hull_sort_by_xyz(before), [pivot], _convex_hull_sort_by_xyz(after));
+        [each _convex_hull_sort_by_xyz(before), pivot, each _convex_hull_sort_by_xyz(after)];
 
 function normal(pts, f) = cross(pts[f[1]] - pts[f[0]], pts[f[2]] - pts[f[0]]);
 
@@ -33,25 +33,25 @@ function m_assign(m, i, j, v) =
     let(
         lt = m[i],
         leng_lt = len(lt),
-        nlt = concat(
+        nlt = [
-            j == 0 ? [] : [for(idx = [0:j - 1]) lt[idx]],
+            each (j == 0 ? [] : [for(idx = [0:j - 1]) lt[idx]]),
-            [v],
+            v,
-            j == leng_lt - 1 ? [] : [for(idx = [j + 1:leng_lt - 1]) lt[idx]]
+            each (j == leng_lt - 1 ? [] : [for(idx = [j + 1:leng_lt - 1]) lt[idx]])
-        ),
+        ],
         leng_m = len(m)
     )
-    concat(
+    [
-        i == 0 ? [] : [for(idx = [0:i - 1]) m[idx]],
+        each (i == 0 ? [] : [for(idx = [0:i - 1]) m[idx]]),
-        [nlt],
+        nlt,
-        i == leng_m - 1 ? [] : [for(idx = [i + 1:leng_m - 1]) m[idx]]
+        each (i == leng_m - 1 ? [] : [for(idx = [i + 1:leng_m - 1]) m[idx]])
-    );
+    ];
 
 function next_vis(i, pts, cur_faces, cur_faces_leng, next, vis, j = 0) = 
     j == cur_faces_leng ? [next, vis] :
     let(
         f = cur_faces[j],
         d = (pts[f[0]] - pts[i]) * normal(pts, f),
-        nx = d >= 0 ? concat(next, [f]) : next,
+        nx = d >= 0 ? [each next, f] : next,
         s = d > 0 ? 1 :
             d < 0 ? -1 : 0,
         vis1 = m_assign(vis, f[0], f[1], s),
@@ -68,11 +68,11 @@ function next2(i, cur_faces, cur_faces_leng, vis, next, j = 0) =
         b = f[1],
         c = f[2],
         nx1 = vis[a][b] < 0 && vis[a][b] != vis[b][a] ? 
-            concat(next, [[a, b, i]]) : next,
+            [each next, [a, b, i]] : next,
         nx2 = vis[b][c] < 0 && vis[b][c] != vis[c][b] ? 
-            concat(nx1, [[b, c, i]]) : nx1,        
+            [each nx1, [b, c, i]] : nx1,        
         nx3 = vis[c][a] < 0 && vis[c][a] != vis[a][c] ? 
-            concat(nx2, [[c, a, i]]) : nx2                    
+            [each nx2, [c, a, i]] : nx2                    
     )
     next2(i, cur_faces, cur_faces_leng, vis, nx3, j + 1);
 

src/__comm__/_vertex_normals.scad

@@ -20,7 +20,7 @@ function _connected_faces(faces, leng, leng_pts, cnt_faces, i = 0) =
 		facei = sort(faces[i], by = ascending),
 		n_cnt_faces = [
 		    for(k = [0:leng_pts - 1])
-			find_index(facei, function(e) e == k) != -1 ? concat(cnt_faces[k], [faces[i]]) : cnt_faces[k]
+			find_index(facei, function(e) e == k) != -1 ? [each cnt_faces[k], faces[i]] : cnt_faces[k]
 		]
 	)
 	_connected_faces(faces, leng, leng_pts, n_cnt_faces, i + 1);

src/voronoi/_impl/_convex_intersection.scad

@@ -19,7 +19,7 @@ function _in_convex(convex_pts, pt) =
 function _intersection_ps(shape, line_pts, epsilon) = 
     let(
         leng = len(shape),
-        pts = concat(shape, [shape[0]])
+        pts = [each shape, shape[0]]
     )
     dedup([
         for(i = [0:leng - 1]) 
@@ -31,7 +31,7 @@ function _convex_intersection(shape1, shape2, epsilon = 0.0001) =
     (shape1 == [] || shape2 == []) ? [] :
     let(
         leng = len(shape1),
-        pts = concat(shape1, [shape1[0]])
+        pts = [each shape1, shape1[0]]
     )
     _convex_ct_clk_order(
         concat(

src/voronoi/_impl/_vrn2_space_cells_impl.scad

@@ -20,16 +20,16 @@ function cell_pt(fcord, grid_w, seed, x, y, gw, gh) =
 
 // 21-nearest-neighbor 
 function _neighbors(fcord, seed, grid_w, gw, gh) = 
+    let(range = [-1:1])
     concat(
         [
-            for(y = [-1:1])
+            for(y = range, x = range)
-                for(x = [-1:1])
                     cell_pt(fcord, grid_w, seed, x, y, gw, gh)
         ],
-        [for(x = [-1:1]) cell_pt(fcord, grid_w, seed, x, -2, gw, gh)],
+        [for(x = range) cell_pt(fcord, grid_w, seed, x, -2, gw, gh)],
-        [for(x = [-1:1]) cell_pt(fcord, grid_w, seed, x, 2, gw, gh)],
+        [for(x = range) cell_pt(fcord, grid_w, seed, x, 2, gw, gh)],
-        [for(y = [-1:1]) cell_pt(fcord, grid_w, seed, -2, y, gw, gh)],
+        [for(y = range) cell_pt(fcord, grid_w, seed, -2, y, gw, gh)],
-        [for(y = [-1:1]) cell_pt(fcord, grid_w, seed, 2, y, gw, gh)]
+        [for(y = range) cell_pt(fcord, grid_w, seed, 2, y, gw, gh)]
     );
 
 function _cells_lt_before_intersection(shape, size, points, pt, half_region_size) =

src/voronoi/vrn_sphere.scad

@@ -6,7 +6,7 @@ function vrn_sphere(points) =
 	    r = norm(points[0]),
 	    plane_pts = [for(p = points) stereographic_proj_to_plane(p / r)],
 		inifinity = [4e7, 0],
-		vrn2_cells = vrn2_cells_from(concat(plane_pts, [inifinity]))
+		vrn2_cells = vrn2_cells_from([each plane_pts, inifinity])
 	)
     [
 		for(i = [0:len(vrn2_cells) - 2])