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

src/__comm__/_convex_hull3.scad

@@ -34,16 +34,16 @@ function m_assign(m, i, j, v) =
         lt = m[i],
         leng_lt = len(lt),
         nlt = [
-            each (j == 0 ? [] : [for(idx = [0:j - 1]) lt[idx]]),
+            if(j != 0) each  [for(idx = [0:j - 1]) lt[idx]],
             v,
-            each (j == leng_lt - 1 ? [] : [for(idx = [j + 1:leng_lt - 1]) lt[idx]])
+            if(j != leng_lt - 1) each [for(idx = [j + 1:leng_lt - 1]) lt[idx]]
         ],
         leng_m = len(m)
     )
     [
-        each (i == 0 ? [] : [for(idx = [0:i - 1]) m[idx]]),
+        if(i != 0) each [for(idx = [0:i - 1]) m[idx]],,
         nlt,
-        each (i == leng_m - 1 ? [] : [for(idx = [i + 1:leng_m - 1]) m[idx]])
+        if(i != leng_m - 1) each [for(idx = [i + 1:leng_m - 1]) m[idx]]
     ];
 
 function next_vis(i, pts, cur_faces, cur_faces_leng, next, vis, j = 0) = 

src/_impl/_archimedean_spiral_impl.scad

@@ -11,10 +11,7 @@ function _find_radians(b, point_distance, radians, n, count = 1) =
         _find_radians(
             b, 
             point_distance, 
-            concat(
+            [each radians, pre_radians + _radian_step(b, pre_radians, point_distance)], 
-                radians,
-                [pre_radians + _radian_step(b, pre_radians, point_distance)]
-            ), 
             n,
         count + 1) 
     );

src/_impl/_bezier_curve_impl.scad

@@ -54,11 +54,5 @@ function _bezier_curve_point3(t, points) =
 function _bezier_curve_impl(t_step, points) = 
     let(t_end = ceil(1 / t_step)) 
     len(points[0]) == 3 ? 
-            concat([
+        [each [for(t = 0; t < t_end; t = t + 1) _bezier_curve_point3(t * t_step, points)], _bezier_curve_point3(1, points)] :
-                for(t = 0; t < t_end; t = t + 1)
+        [each [for(t = 0; t < t_end; t = t + 1) _bezier_curve_point2(t * t_step, points)], _bezier_curve_point2(1, points)];
-                    _bezier_curve_point3(t * t_step, points)
-            ], [_bezier_curve_point3(1, points)]) :
-            concat([
-                for(t = 0; t < t_end; t = t + 1)
-                    _bezier_curve_point2(t * t_step, points)
-            ], [_bezier_curve_point2(1, points)]);

src/_impl/_bezier_smooth_impl.scad

@@ -54,11 +54,6 @@ function _bezier_smooth_impl(path_pts, round_d, t_step, closed, angle_threshold)
                     [pts[leng - 2], pts[leng - 1], pts[0]],
                     round_d, t_step, 3, angle_threshold
                 )  
-            ) :
+            ) : [pts[0], each middle_pts, pts[leng - 1]]
-            concat(
-                [pts[0]],
-                middle_pts,
-                [pts[leng - 1]]
-            )
     ) 
     len(path_pts[0]) == 2 ? [for(p = pth_pts) __to2d(p)] : pth_pts;

src/_impl/_bijection_offset_impl.scad

@@ -40,9 +40,9 @@ function _bijection_offset_impl(pts, d, epsilon) =
         leng_minus_one = leng - 1,
         last_p = __line_intersection2(offset_es[leng_minus_one], offset_es[0], epsilon)
     )
-    concat(
+    [
-        last_p != [] && last_p == last_p ? [last_p] : [],
+        if(last_p != [] && last_p == last_p) last_p,
-        [
+        each [
             for(i = 0; i < leng_minus_one; i = i + 1)
             let(
                 this_edge = offset_es[i],
@@ -53,5 +53,5 @@ function _bijection_offset_impl(pts, d, epsilon) =
             )
             p
         ]
-    );
+    ];
     

src/_impl/_bspline_curve_impl.scad

@@ -54,7 +54,7 @@ function _bspline_curve_interpolate(t, degree, points, knots, weights) =
         v = [
             for(i = 0; i < n; i = i + 1) 
             let(p = points[i] * wts[i])
-            concat([for(j = 0; j < d; j = j + 1) p[j]], [wts[i]])
+            [each [for(j = 0; j < d; j = j + 1) p[j]], wts[i]]
         ],
         ts = _bspline_curve_ts(t, degree, kts),
         s = ts[1],

src/_impl/_midpt_smooth_impl.scad

@@ -1,11 +1,11 @@
 function _midpt_smooth_sub(points, iend, closed) = 
-    concat(
+    [
-        [
+        each [
             for(i = 0; i < iend; i = i + 1) 
                 (points[i] + points[i + 1]) / 2
         ],
-        closed ? [(points[iend] + points[0]) / 2] : []
+        if(closed) (points[iend] + points[0]) / 2
-    );
+    ];
 
 function _midpt_smooth_impl(points, n, closed) =
     let(

src/_impl/_shape_path_extend_impl.scad

@@ -73,6 +73,6 @@ function _shape_path_extend_impl(stroke_pts, path_pts, scale, closed) =
     closed && path_pts[0] == path_pts[leng_path_pts - 1] ? 
         __polytransversals(concat(strokes, [strokes[0]])) : 
         __polytransversals(
-            concat([_shape_path_first_stroke(stroke_pts, path_pts)], strokes)
+            [_shape_path_first_stroke(stroke_pts, path_pts), each strokes]
         );
         

src/_impl/_trim_shape_impl.scad

@@ -23,13 +23,12 @@ function _trim_sub(lines, leng, epsilon) =
         inter_p = _trim_shape_any_intersection(lines_from_next2, current_line, leng_lines_from_next2, 0, epsilon)
     )
     // no intersecting pt, collect current_p and trim remain lines
-    inter_p == [] ? (concat([current_p], _trim_shape_trim_lines(lines_from_next, epsilon))) : (
+    inter_p == [] ? [current_p, each _trim_shape_trim_lines(lines_from_next, epsilon)]
+         : (
         // collect current_p, intersecting pt and the last pt
         (leng == 3 || (inter_p.x == (leng_lines_from_next2 - 1))) ? [current_p, inter_p.y, lines[leng - 1]] : (
             // collect current_p, intersecting pt and trim remain lines
-            concat([current_p, inter_p.y], 
+            [current_p, inter_p.y, each _trim_shape_trim_lines([for(i = inter_p.x + 1; i < leng_lines_from_next2; i = i + 1) lines_from_next2[i]], epsilon)]
-                _trim_shape_trim_lines([for(i = inter_p.x + 1; i < leng_lines_from_next2; i = i + 1) lines_from_next2[i]], epsilon)
-            )
         )
     );
     
@@ -38,7 +37,7 @@ function _trim_shape_trim_lines(lines, epsilon) =
     leng > 2 ? _trim_sub(lines, leng, epsilon) : _trim_shape_collect_pts_from(lines, leng);
 
 function _trim_shape_collect_pts_from(lines, leng) = 
-    concat([for(line = lines) line[0]], [lines[leng - 1][1]]);
+    [each [for(line = lines) line[0]], lines[leng - 1][1]];
 
 function _trim_shape_impl(shape_pts, from, to, epsilon) = 
     let(

src/arc_path.scad

@@ -18,10 +18,9 @@ function arc_path(radius, angle) =
         angles = is_num(angle) ? [0, angle] : angle,
         m = floor(angles[0] / a_step) + 1,
         n = floor(angles[1] / a_step),
-        points = concat([__ra_to_xy(__edge_r_begin(radius, angles[0], a_step, m), angles[0])],
+        points = [
-            m > n ? [] : [
+            __ra_to_xy(__edge_r_begin(radius, angles[0], a_step, m), angles[0]),
-                for(i = m; i <= n; i = i + 1)
+            if(m <= n) each [for(i = m; i <= n; i = i + 1) __ra_to_xy(radius, a_step * i)],
-                    __ra_to_xy(radius, a_step * i)
+            if(angles[1] != a_step * n) __ra_to_xy(__edge_r_end(radius, angles[1], a_step, n), angles[1])
-            ],
+        ]
-            angles[1] == a_step * n ? [] : [__ra_to_xy(__edge_r_end(radius, angles[1], a_step, n), angles[1])])
     ) points;

src/curve.scad

@@ -12,13 +12,13 @@ use <_impl/_catmull_rom_spline.scad>;
 
 function curve(t_step, points, tightness = 0) = 
     let(leng = len(points))
-    concat(
+    [
-        [
+        each [
             for(i = [0:leng - 4])
                 let(
                     pts = _catmull_rom_spline_4pts(t_step, [for(j = [i:i + 3]) points[j]], tightness)
                 )
                 for(i = [0:len(pts) - 2]) pts[i]    
         ],
-        [points[leng - 2]]
+        points[leng - 2]
-    );
+    ];

src/ellipse_extrude.scad

@@ -30,14 +30,8 @@ module ellipse_extrude(semi_minor_axis, height, center = false, convexity = 10,
                 pre_f * f_extrude[i][0]
         ];
 
-    child_fs = concat([1], accm_fs);
+    child_fs = [1, each accm_fs];
-    pre_zs = concat(
+    pre_zs = [0, each [for(i = 0; i < len_f_extrude; i = i + 1) f_extrude[i][1]]];
-        [0],
-        [
-            for(i = 0; i < len_f_extrude; i = i + 1)
-                f_extrude[i][1]
-        ]
-    );
 
     module extrude() {
         for(i = [0:len_f_extrude - 1]) {

src/experimental/_impl/Gyroid3.scad

@@ -91,7 +91,7 @@ function gyroid_points(pp, w)=
 // pp=number of rows
 function gyroid_faces(pp)=
 	let(zs=(pp+1)*(pp+1))								// starting index of down wall points
-	concat(												// calculate face index vetros for triangles of polyhedron
+	  		     										// calculate face index vetros for triangles of polyhedron
 	[	for(i=[0:pp-1])									// for every row
 			let(jm=i*(i+1))								// middle point index for current j vector
 			let(jfm=(i+1)*(i+2))						// middle point index for succeeding j vector
@@ -103,7 +103,7 @@ function gyroid_faces(pp)=
 				let(p3=(l==0) ? jfm+(j+1)*k+dm : jm+(j+1)*k+dm)
 				if (j<i || l==0)
 					((k==1 && m==0) || (k==-1 && m==1)) ? [p2, p1, p3] : [p1, p2, p3]
-	]);
+	];
 
 // Swaps x and y coordinate of all members in matrix m. Applied on a faces matrix for polyhedron creation, it swaps inside out. 
 function swap_xy(m)=

src/experimental/_impl/_convex_intersection_impl.scad

@@ -3,7 +3,7 @@ use <lines_intersection.scad>;
 function _intersection_ps(shape, line_pts, epsilon) = 
     let(
         leng = len(shape),
-        pts = concat(shape, [shape[0]])
+        pts = [each shape, shape[0]]
     )
     [
         for(i = [0:leng - 1]) 

src/experimental/_impl/_tiles_wfc_impl.scad

@@ -252,13 +252,12 @@ function tilemap_generate(tm) =
 		], x, y));
 
 
-function neighbor_dirs(x, y, width, height) =
+function neighbor_dirs(x, y, width, height) = [
-    concat(
+	if(x > 0)          [-1,  0],   // left
-		x > 0          ? [[-1,  0]] : [],  // left
+	if(x < width - 1)  [ 1,  0],   // right 
-		x < width - 1  ? [[ 1,  0]] : [],  // right 
+	if(y > 0)          [ 0, -1],   // top
-		y > 0          ? [[ 0, -1]] : [],  // top
+	if(y < height - 1) [ 0,  1]    // bottom
-		y < height - 1 ? [[ 0,  1]] : []   // bottom
+];
-	);
 
 function neighbor_compatibilities(sample, x, y, width, height) = 
     let(me = sample[y][x])

src/experimental/convex_intersection.scad

@@ -7,7 +7,7 @@ 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/experimental/hollow_out_sweep.scad

@@ -29,7 +29,7 @@ module hollow_out_sweep(sections, diameter, closed = false, style = "LINES") {
             [[rect[0], rect[1], rect[2]], [rect[0], rect[2], rect[3]]] :
             [[rect[1], rect[2], rect[3]], [rect[1], rect[3], rect[0]]];        
     
-    sects = closed ? concat(sections, [sections[0]]) : sections;
+    sects = closed ? [each sections, sections[0]] : sections;
     lines = [
         for(rect = rects(sects)) 
             for(tri = rand_tris(rect)) 

src/experimental/tile_penrose2.scad

@@ -67,9 +67,9 @@ function sub_dart(tile) =
 		n_size = tile_size(tile) / PHI,
 		r = PHI * size
 	)
-	concat(
+	[
-		[tile(KITE, x, y, between_360(angle + 5 * 36), n_size)],
+		tile(KITE, x, y, between_360(angle + 5 * 36), n_size),
-		[
+		each [
 			for(i = 0, sign = 1; i < 2; i = i + 1, sign = -sign)
 			let(a = between_360(angle - 4 * 36 * sign))
 			tile(
@@ -80,7 +80,7 @@ function sub_dart(tile) =
 				n_size
 			)
 		]
-	);
+	];
 
 function subdivide(tiles) = [
     for(tile = tiles)
@@ -114,9 +114,9 @@ function tile_penrose2(n, triangles) =
 			angle = tile_angle(tile) - 36,
 			type = tile_type(tile),
 			size = tile_size(tile),
-			shape = concat(
+			shape = [
-				[[tile_x(tile), tile_y(tile)]],
+				[tile_x(tile), tile_y(tile)],
-				[
+				each [
 					for(i = [0:2])
 					let(
 						r = dist[type][i] * size,
@@ -124,7 +124,7 @@ function tile_penrose2(n, triangles) =
 					)
 					[tile_x(tile) + r * cos(a), tile_y(tile) + r * sin(a)]
 				]
-			)
+			]
 		)
 		each [
 		    [type, [shape[0], shape[1], shape[2]]], 

src/experimental/tile_penrose3.scad

@@ -25,7 +25,7 @@ function _sub_obtuse(a, b, c) =
 		PHI = 1.618033988749895,
 		r = b + (c - b) / PHI
 	) 
-	concat([["OBTUSE", r, c, a]], _sub_acute(b, a, r));
+	[["OBTUSE", r, c, a], each _sub_acute(b, a, r)];
 
 function _penrose3(triangles, n, i = 0) = 
 	i == n ? triangles :

src/hexagons.scad

@@ -59,13 +59,7 @@ module hexagons(radius, spacing, levels) {
         [[hex_datum[0][0], -hex_datum[0][1]], hex_datum[1]]
     ] : [];
 
-    total_hex_data = concat(
+    total_hex_data = [[[0, 0], beginning_n], each upper_hex_data, each lower_hex_data];
-        [
-            [[0, 0], beginning_n] // first line
-        ], 
-        upper_hex_data, 
-        lower_hex_data
-    );
 
     pts_all_lines = [
         for(hex_datum = total_hex_data)

src/loft.scad

@@ -29,11 +29,7 @@ module loft(sections, slices = 1) {
             p1 = sect[i],
             p2 = sect[(i + 1) % leng]
         )
-        concat(
+        [p1, each inter_pts(p1, p2, n), each _interpolate(sect, leng, n, i + 1)];
-            [p1], 
-            inter_pts(p1, p2, n),
-            _interpolate(sect, leng, n, i + 1)
-        );
 
     function interpolate(sect, n) = 
         n <= 1 ? sect : _interpolate(sect, len(sect), n);
@@ -53,13 +49,7 @@ module loft(sections, slices = 1) {
         new_sect1 = interpolate(sect1, lcm_n / len(sect1));
         new_sect2 = interpolate(sect2, lcm_n / len(sect2));
         
-        sweep(
+        sweep([new_sect1, each inter_sects(new_sect1, new_sect2, lcm_n, slices), new_sect2]);
-            concat(
-                [new_sect1],
-                inter_sects(new_sect1, new_sect2, lcm_n, slices),
-                [new_sect2]
-            )
-        );
     }
         
     for(i = [0:len(sections) - 2]) {

src/maze/_impl/_mz_hamiltonian_impl.scad

@@ -51,6 +51,4 @@ function _mz_hamiltonian_travel(dot_pts, p, leng, i = 0) =
         dir_i = _mz_hamiltonian_dir(_mz_hamiltonian_corner_value(dot_pts, p.x, p.y)),
         nxt_p = p + _mz_hamiltonian_nxt_offset[dir_i]
     )
-    concat(
+    [p, each _mz_hamiltonian_travel(dot_pts, nxt_p, leng, i + 1)];
-        [p], _mz_hamiltonian_travel(dot_pts, nxt_p, leng, i + 1)
-    );

src/maze/_impl/_mz_theta_cells.scad

@@ -32,7 +32,7 @@ function set_outwards(cell, outwards) = [
 function get_outwards(cell) = cell[5];
 
 function add_outward(cell, outward) = [
-	cell[0], cell[1], cell[2], cell[3], cell[4], concat(get_outwards(cell), [outward]), cell[6], cell[7]
+	cell[0], cell[1], cell[2], cell[3], cell[4], [each get_outwards(cell), outward], cell[6], cell[7]
 ];
 
 function columnLengOfRow(ri, cellWidth, previousColumnLeng, dividedRatio) = 
@@ -63,7 +63,7 @@ function _init_theta_maze(ri, maze, totalRows, dividedRatio, cellWidth) =
 					cell(ri, ci, INWARD_CCW_WALL)
 			]
 		)
-		_init_theta_maze(ri + 1, concat(maze, [row]), totalRows, dividedRatio, cellWidth);
+		_init_theta_maze(ri + 1, [each maze, row], totalRows, dividedRatio, cellWidth);
 
 function update_maze_row(row, cell) =
     let(leng = len(row))

src/noise/_impl/_nz_cell_impl.scad

@@ -26,7 +26,7 @@ function _nz_cell_border(cells, p) =
     let(
         dists = [
             for(i = [0:len(cells) - 1])
-                concat(cells[i], [norm(cells[i] - p)])
+                [each cells[i], norm(cells[i] - p)]
         ],
         idx = len(cells[0]),
         sorted = sort(dists, by = "idx", idx = idx),

src/path_extrude.scad

@@ -89,7 +89,7 @@ module path_extrude(shape_pts, path_pts, triangles = "SOLID", twist = 0, scale =
                 curr_matrix = rot_matrice[i],
                 prev_matrix = matrice[len(matrice) - 1]
             )
-            concat(matrice, [curr_matrix * prev_matrix]);
+            [each matrice, curr_matrix * prev_matrix];
 
         cumu_rot_matrice = cumulated_rot_matrice(0);
 
@@ -137,11 +137,11 @@ module path_extrude(shape_pts, path_pts, triangles = "SOLID", twist = 0, scale =
                             pth_pts[i + 1]
                         )
                 ]
-            ) concat([fst_section], remain_sections);
+            ) [fst_section, each remain_sections];
 
         calculated_sections =
             closed && pth_pts[0] == pth_pts[len_path_pts_minus_one] ?
-                concat(sections, [sections[0]]) : // round-robin
+                [each sections, sections[0]] : // round-robin
                 sections;
         
         sweep(
@@ -186,8 +186,8 @@ module path_extrude(shape_pts, path_pts, triangles = "SOLID", twist = 0, scale =
 
         calculated_sections =
             closed && pth_pts[0] == pth_pts[len_path_pts_minus_one] ?
-                concat(path_extrude_inner, [path_extrude_inner[0]]) : // round-robin
+                [each path_extrude_inner, path_extrude_inner[0]] : // round-robin
-                concat([section(pth_pts[0], pth_pts[1], 0)], path_extrude_inner);
+                [section(pth_pts[0], pth_pts[1], 0), each path_extrude_inner];
 
         sweep(
             calculated_sections,

src/polyhedra/geom_star.scad

@@ -5,8 +5,8 @@ function geom_star(outerRadius = 1, innerRadius =  0.381966, height = 0.5, n = 5
         half_thetaStep = thetaStep / 2,
         half_height = height / 2,
         leng_star = n * 2,
-        points = concat(
+        points = [
-            [
+            each [
                 for(i = [0:n - 1]) 
                 let(
                     a = thetaStep * i + right,
@@ -15,8 +15,9 @@ function geom_star(outerRadius = 1, innerRadius =  0.381966, height = 0.5, n = 5
                 )
                 each [outerPoint, innerPoint]
             ],
-            [[0, 0, half_height], [0, 0, -half_height]]
+            [0, 0, half_height], 
-        ),
+            [0, 0, -half_height]
+        ],
         faces = [
             for(i = [0:leng_star - 1]) 
                 each [[leng_star, (i + 1) % leng_star, i], [i, (i + 1) % leng_star, leng_star + 1]]

src/ring_extrude.scad

@@ -31,24 +31,17 @@ module ring_extrude(shape_pts, radius, angle = 360, twist = 0, scale = 1.0, tria
         begin_r = leng / cos((m - 0.5) * a_step - angles[0]);
         end_r =  leng / cos((n + 0.5) * a_step - angles[1]);
 
-        angs = concat(
+        angs = [[90, 0, angles[0]], each (m > n ? [] : [for(i = [m:n]) [90, 0, a_step * i]])];
-            [[90, 0, angles[0]]], 
+
-            m > n ? [] : [for(i = [m:n]) [90, 0, a_step * i]]
+        pts = [__ra_to_xy(begin_r, angles[0]), each (m > n ? [] : [for(i = [m:n]) __ra_to_xy(radius, a_step * i)])];
-        );
-        pts = concat(
-            [__ra_to_xy(begin_r, angles[0])],
-            m > n ? [] : [for(i = [m:n]) __ra_to_xy(radius, a_step * i)]
-        ); 
 
         is_angle_frag_end = angs[len(angs) - 1][2] == angles[1];
         
         all_angles = is_angle_frag_end ? 
-            angs :  
+            angs : [each angs, [90, 0, angles[1]]];
-            concat(angs, [[90, 0, angles[1]]]);
             
         all_points = is_angle_frag_end ? 
-            pts :
+            pts : [each pts, __ra_to_xy(end_r, angles[1])];
-            concat(pts, [__ra_to_xy(end_r, angles[1])]);
 
         sections = cross_sections(shape_pts, all_points, all_angles, twist, scale);
 

src/rounded_cylinder.scad

@@ -13,11 +13,7 @@ use <__comm__/__half_trapezium.scad>;
 module rounded_cylinder(radius, h, round_r, convexity = 2, center = false) {  
     r_corners = __half_trapezium(radius, h, round_r);
     
-    shape_pts = concat(
+    shape_pts = [[0, -h/2], each r_corners, [0, h/2]];
-        [[0, -h/2]],
-        r_corners,           
-        [[0, h/2]]
-    );
 
     center_pt = center ? [0, 0, 0] : [0, 0, h/2];
 

src/shape_arc.scad

@@ -23,21 +23,19 @@ function shape_arc(radius, angle, width, width_mode = "LINE_CROSS") =
         n = floor(angles[1] / a_step),
         r_outer = radius + w_offset[0],
         r_inner = radius + w_offset[1],
-        points = concat(
+        points = [
             // outer arc path
-            [__ra_to_xy(__edge_r_begin(r_outer, angles[0], a_step, m), angles[0])],
+            __ra_to_xy(__edge_r_begin(r_outer, angles[0], a_step, m), angles[0]),
-            m > n ? [] : [
+            if(m <= n) each [for(i = m; i <= n; i = i + 1)  __ra_to_xy(r_outer, a_step * i)],
-                for(i = m; i <= n; i = i + 1)  __ra_to_xy(r_outer, a_step * i)
+            if(angles[1] != a_step * n) __ra_to_xy(__edge_r_end(r_outer, angles[1], a_step, n), angles[1]),
-            ],
-            angles[1] == a_step * n ? [] : [__ra_to_xy(__edge_r_end(r_outer, angles[1], a_step, n), angles[1])],
             // inner arc path
-            angles[1] == a_step * n ? [] : [__ra_to_xy(__edge_r_end(r_inner, angles[1], a_step, n), angles[1])],
+            if(angles[1] != a_step * n) __ra_to_xy(__edge_r_end(r_inner, angles[1], a_step, n), angles[1]),
-            m > n ? [] : [
+            if(m <= n) each [
                 for(i = m; i <= n; i = i + 1)
-                    let(idx = (n + (m - i)))
+                let(idx = (n + (m - i)))
-                    __ra_to_xy(r_inner, a_step * idx)
+                __ra_to_xy(r_inner, a_step * idx)
 
             ],
-            [__ra_to_xy(__edge_r_begin(r_inner, angles[0], a_step, m), angles[0])]        
+            __ra_to_xy(__edge_r_begin(r_inner, angles[0], a_step, m), angles[0])
-        )
+        ]
     ) points;

src/shape_pie.scad

@@ -20,13 +20,14 @@ function shape_pie(radius, angle) =
         n = floor(angles[1] / a_step),
         edge_r_begin = leng / cos((m - 0.5) * a_step - angles[0]),
         edge_r_end = leng / cos((n + 0.5) * a_step - angles[1]),
-        shape_pts = concat(
+        shape_pts = [
-            [[0, 0], __ra_to_xy(edge_r_begin, angles[0])],
+            [0, 0], 
-            m > n ? [] : [
+            __ra_to_xy(edge_r_begin, angles[0]), 
+            if(m <= n) each [
                 for(i = m; i <= n; i = i + 1)
-                    let(a = a_step * i) 
+                let(a = a_step * i) 
-                    __ra_to_xy(radius, a)
+                __ra_to_xy(radius, a)
             ],
-            angles[1] == a_step * n ? [] : [__ra_to_xy(edge_r_end, angles[1])]
+            if(angles[1] != a_step * n) __ra_to_xy(edge_r_end, angles[1])
-        )
+        ]
     ) shape_pts;

src/surface/sf_thickenT.scad

@@ -36,7 +36,7 @@ module sf_thickenT(points, thickness, triangles = undef, direction = "BOTH", con
 			tri = sort(triangles[i], by = ascending),
             n_cnt_tris = [
                 for(k = [0:leng_pts - 1])
-                find_index(tri, function(e) e == k) != -1 ? concat(cnt_tris[k], [triangles[i]]) : cnt_tris[k]
+                find_index(tri, function(e) e == k) != -1 ? [each cnt_tris[k], triangles[i]] : cnt_tris[k]
             ]
 		)
 		_connected_tris(triangles, leng, leng_pts, n_cnt_tris, i + 1);

src/sweep.scad

@@ -96,7 +96,7 @@ module sweep(sections, triangles = "SOLID") {
                     i + leng_pts_sect * (leng_sects - 1)
             ];    
 
-            f_idxes = concat([first_idxes], side_indexes(sects), [last_idxes]);
+            f_idxes = [first_idxes, each side_indexes(sects), last_idxes];
             
             polyhedron(
                 v_pts, 

src/triangle/_impl/_tri_delaunay_impl.scad

@@ -156,7 +156,7 @@ function updateNbrs(d, delaunayTri, neighbors, _indices_hash) =
 	
 function delaunayAddCoords(d, p) = 
     [
-	    concat(delaunay_coords(d), [p]), 
+		[each delaunay_coords(d), p], 
 		delaunay_triangles(d), 
 		delaunay_circles(d)
 	];
@@ -206,10 +206,10 @@ function _delaunayBoundaries(d, badTriangles, boundaries, t, vi, _indices_hash)
 		)
 		_delaunayBoundaries(d, badTriangles, boundaries, nt, nvi, _indices_hash) : 
 	    let(
-		    nboundaries = concat(boundaries, [[
+		    nboundaries = [each boundaries, [
 			    [t[(vi + 1) % 3], t[vi > 0 ? vi - 1 : (vi + 2)]], // edge
 				opTri                                             // delaunayTri
-			]]),
+			]],
 			nvi = (vi + 1) % 3,
 			v1 = nboundaries[0][0][0],
 			v2 = nboundaries[len(nboundaries) - 1][0][1]

src/triangle/_impl/_tri_ear_clipping_impl.scad

@@ -68,7 +68,7 @@ function _triangulate_snip(shape_pts, collector, indices, u, v, w, num_of_vertic
     )
     _triangulate_real_triangulate( 
         shape_pts, 
-        concat(collector, [[a, b, c]]),  
+        [each collector, [a, b, c]],  
         _triangulate_remove_v(indices, v, num_of_vertices),
         v, 
         new_nv,

src/turtle/_impl/_footprints2.scad

@@ -6,4 +6,4 @@ function _footprints2(cmds, t, leng, i = 0) =
             nxt = turtle2d(cmds[i][0], t, cmds[i][1]),
             pts = _footprints2(cmds, nxt, leng, i + 1)
         )
-        cmds[i][0] != "forward" ? pts : concat([turtle2d("pt", nxt)], pts);
+        cmds[i][0] != "forward" ? pts : [turtle2d("pt", nxt), each pts];

src/turtle/_impl/_footprints3.scad

@@ -6,4 +6,4 @@ function _footprints3(cmds, t, leng, i = 0) =
             nxt = turtle3d(cmds[i][0], t, cmds[i][1]),
             pts = _footprints3(cmds, nxt, leng, i + 1)
         )
-        cmds[i][0] != "forward" && cmds[i][0] != "yu_move" && cmds[i][0] != "zu_move" ? pts : concat([turtle3d("pt", nxt)], pts);
+        cmds[i][0] != "forward" && cmds[i][0] != "yu_move" && cmds[i][0] != "zu_move" ? pts : [turtle3d("pt", nxt), each pts];

src/turtle/_impl/_lsystem2_impl.scad

@@ -8,7 +8,7 @@ function _lsystem2_derive(axiom, rules, n, rule_prs) =
                          _derive_p(axiom, rules, rule_prs, n);
 
 function _next_stack(t, code, stack) = 
-    code == "[" ? concat([t], stack) :
+    code == "[" ? [t, each stack] :
     let(leng = len(stack))
     code == "]" ? 
             (leng > 1 ? [for(i = [1:leng - 1]) stack[i]] : []) :

src/turtle/_impl/_lsystem3_impl.scad

@@ -8,7 +8,7 @@ function _lsystem3_derive(axiom, rules, n, rule_prs) =
                          _derive_p(axiom, rules, rule_prs, n);
 
 function _next_stack(t, code, stack) = 
-    code == "[" ? concat([t], stack) :
+    code == "[" ? [t, each stack] :
     let(leng = len(stack))
     code == "]" ? 
             (leng > 1 ? [for(i = [1:leng - 1]) stack[i]] : []) :

src/turtle/footprints2.scad

@@ -16,4 +16,4 @@ function footprints2(cmds, start = [0, 0]) =
         t = turtle2d("create", start.x, start.y, 0),
         leng = len(cmds)
     )
-    concat([turtle2d("pt", t)], _footprints2(cmds, t, leng));
+    [turtle2d("pt", t), each _footprints2(cmds, t, leng)];

src/turtle/footprints3.scad

@@ -16,4 +16,4 @@ function footprints3(cmds, start = [0, 0, 0]) =
         t = turtle3d("create", start, [[1, 0, 0], [0, 1, 0], [0, 0, 1]]),
         leng = len(cmds)
     )
-    concat([turtle3d("pt", t)], _footprints3(cmds, t, leng));
+    [turtle3d("pt", t), each _footprints3(cmds, t, leng)];

src/util/_impl/_dedup_impl.scad

@@ -15,4 +15,4 @@ function _dedup_add(buckets, i_elem, eq, hash, bucket_numbers) =
 
 function _add(buckets, bucket, i_elem, b_idx) = 
     let(leng = len(buckets))
-	[for(i = 0; i < leng; i = i + 1) i == b_idx ? concat(bucket, [i_elem]) : buckets[i]];
+	[for(i = 0; i < leng; i = i + 1) i == b_idx ? [each bucket, i_elem] : buckets[i]];

src/util/_impl/_fibseq_impl.scad

@@ -3,7 +3,7 @@ use <../../__comm__/__fast_fibonacci.scad>;
 function _fibonacci_sequence(seq, n, i = 2) =
     i > n ? seq :
     _fibonacci_sequence(
-        concat(seq, [seq[i - 1] + seq[i - 2]]),
+        [each seq, seq[i - 1] + seq[i - 2]],
         n,
         i + 1
     );    

src/util/_impl/_sort_impl.scad

@@ -8,7 +8,7 @@ function _vt_sort(lt) =
             before = [for(j = 1; j < leng; j = j + 1) if(lessThan(lt[j], pivot)) lt[j]],
             after =  [for(j = 1; j < leng; j = j + 1) if(greaterThan(lt[j], pivot) || lt[j] == pivot) lt[j]]
         )
-        concat(_vt_sort(before), [pivot], _vt_sort(after));
+        [each _vt_sort(before), pivot, each _vt_sort(after)];
 
 function _sort_by_idx(lt, i) = 
     let(leng = len(lt))
@@ -18,7 +18,7 @@ function _sort_by_idx(lt, i) =
             before = [for(j = 1; j < leng; j = j + 1) if(lt[j][i] < pivot[i]) lt[j]],
             after =  [for(j = 1; j < leng; j = j + 1) if(lt[j][i] >= pivot[i]) lt[j]]
         )
-        concat(_sort_by_idx(before, i), [pivot], _sort_by_idx(after, i));
+        [each _sort_by_idx(before, i), pivot, each _sort_by_idx(after, i)];
 
 function _sort_by(lt, by, idx) =
     let(
@@ -35,4 +35,4 @@ function _sort_by_cmp(lt, cmp) =
             before = [for(j = 1; j < leng; j = j + 1) if(cmp(lt[j], pivot) < 0) lt[j]],
             after =  [for(j = 1; j < leng; j = j + 1) if(cmp(lt[j], pivot) >= 0) lt[j]]
         )
-        concat(_sort_by_cmp(before, cmp), [pivot], _sort_by_cmp(after, cmp));
+        [each _sort_by_cmp(before, cmp), pivot, each _sort_by_cmp(after, cmp)];

src/util/_impl/_split_str_impl.scad

@@ -2,13 +2,7 @@ use <../sub_str.scad>;
 
 function _split_t_by(idxs, t) =
     let(leng = len(idxs))
-    concat(
+    [sub_str(t, 0, idxs[0]), each [for(i = 0; i < leng; i = i + 1) sub_str(t, idxs[i] + 1, idxs[i + 1])]];
-        [sub_str(t, 0, idxs[0])],
-        [
-            for(i = 0; i < leng; i = i + 1)
-                sub_str(t, idxs[i] + 1, idxs[i + 1])
-        ]
-    );
              
 function _split_str_impl(t, delimiter) = 
     len(search(delimiter, t)) == 0 ? 

src/util/_impl/_zip_impl.scad

@@ -2,6 +2,9 @@ _identity = function(elems) elems;
 
 function _zipAll_sub(lts, list_to, elem_to, combine, i = 0) = 
     i > elem_to ? [] :
-    concat([combine([for(j = [0:list_to]) lts[j][i]])], _zipAll_sub(lts, list_to, elem_to, combine, i + 1));
+    concat(
+        [combine([for(j = [0:list_to]) lts[j][i]])], 
+        _zipAll_sub(lts, list_to, elem_to, combine, i + 1)
+    );
 
 function _zipAll(lts, combine = _identity) = _zipAll_sub(lts, len(lts) - 1, len(lts[0]) - 1, combine);

src/util/map/_impl/_hashmap_put_impl.scad

@@ -18,4 +18,4 @@ function _replace(buckets, b_numbers, bucket, key, value, b_idx, k_idx) =
 	[for(i = 0; i < b_numbers; i = i + 1) i == b_idx ? n_bucket : buckets[i]];
 
 function _put(buckets, b_numbers, bucket, key, value, b_idx) = 
-    [for(i = 0; i < b_numbers; i = i + 1) i == b_idx ? concat(bucket, [[key, value]]) : buckets[i]];
+    [for(i = 0; i < b_numbers; i = i + 1) i == b_idx ? [each bucket, [key, value]] : buckets[i]];

src/util/map/hashmap_keys.scad

@@ -8,8 +8,4 @@
 *
 **/
 
-function hashmap_keys(map) = [
+function hashmap_keys(map) = [for(bucket = map, kv = bucket) kv[0]];
-    for(bucket = map) 
-        for(kv = bucket)
-            kv[0]
-];

src/util/map/hashmap_values.scad

@@ -8,8 +8,4 @@
 *
 **/
 
-function hashmap_values(map) = [
+function hashmap_values(map) = [for(bucket = map, kv = bucket) kv[1]];
-    for(bucket = map) 
-        for(kv = bucket)
-            kv[1]
-];

src/util/set/_impl/_hashset_add_impl.scad

@@ -8,4 +8,4 @@ function _hashset_add(buckets, b_numbers, elem, eq, hash) =
 	some(bucket, function(e) eq(e, elem)) ? buckets : _add(buckets, b_numbers, bucket, elem, idx);
 
 function _add(buckets, b_numbers, bucket, elem, idx) = 
-	[for(i = 0; i < b_numbers; i = i + 1) i == idx ? concat(bucket, [elem]) : buckets[i]];
+	[for(i = 0; i < b_numbers; i = i + 1) i == idx ? [each bucket, elem] : buckets[i]];

src/util/swap.scad

@@ -15,10 +15,10 @@ function swap(lt, i, j) =
 		a = min([i, j]),
 		b = max([i, j])
 	)
-    concat(
+	[
-	    a == 0 ? [] : [for(idx = [0:a - 1]) lt[idx]], 
+        each (a == 0 ? [] : [for(idx = [0:a - 1]) lt[idx]]),
-		[lt[b]], 
+		lt[b],
-		b - a == 1? [] : [for(idx = [a + 1:b - 1]) lt[idx]], 
+		each (b - a == 1 ? [] : [for(idx = [a + 1:b - 1]) lt[idx]]),
-		[lt[a]], 
+		lt[a],
-		b == leng - 1 ? [] : [for(idx = [b + 1:leng - 1]) lt[idx]]
+		each (b == leng - 1 ? [] : [for(idx = [b + 1:leng - 1]) lt[idx]])
-	);
+	];

src/voronoi/vrn2_space.scad

@@ -29,16 +29,13 @@ module vrn2_space(size, grid_w, seed, spacing = 1, r = 0, delta = 0, chamfer = f
 
     // 21-nearest-neighbor 
     function _neighbors(fcord, seed, grid_w, gw, gh) = 
+        let(range = [-1:1])
         concat(
-            [
+            [for(y = range, x = range) cell_pt(fcord, seed, x, y, gw, gh)],
-                for(y = [-1:1])
+            [for(x = range) cell_pt(fcord, seed, x, -2, gw, gh)],
-                    for(x = [-1:1])
+            [for(x = range) cell_pt(fcord, seed, x, 2, gw, gh)],
-                        cell_pt(fcord, seed, x, y, gw, gh)
+            [for(y = range) cell_pt(fcord, seed, -2, y, gw, gh)],
-            ],
+            [for(y = range) cell_pt(fcord, seed, 2, y, gw, gh)]
-            [for(x = [-1:1]) cell_pt(fcord, seed, x, -2, gw, gh)],
-            [for(x = [-1:1]) cell_pt(fcord, seed, x, 2, gw, gh)],
-            [for(y = [-1:1]) cell_pt(fcord, seed, -2, y, gw, gh)],
-            [for(y = [-1:1]) cell_pt(fcord, seed, 2, y, gw, gh)]
         );
 
     region_size = grid_w * 3;

src/voxel/_impl/_vx_bezier_impl.scad

@@ -8,7 +8,7 @@ function _vx_bezier_pt3(p1, p2, p3, p4, pts) =
         c = (b1 + b2) * 0.5,
         p = [round(c[0]), round(c[1]), round(c[2])]
     )
-    _vx_bezier3(c, b2, a3, p4, _vx_bezier3(p1, a1, b1, c, concat(pts, [p])));
+    _vx_bezier3(c, b2, a3, p4, _vx_bezier3(p1, a1, b1, c, [each pts, p]));
 
 function _vx_bezier3(p1, p2, p3, p4, pts) =
     (abs(p1[0] - p4[0]) < 0.5 && abs(p1[1] - p4[1]) < 0.5 && abs(p1[2] - p4[2]) < 0.5) ? 
@@ -25,7 +25,7 @@ function _vx_bezier_pt2(p1, p2, p3, p4, pts) =
         c = (b1 + b2) * 0.5,
         p = [round(c[0]), round(c[1])]
     )
-    _vx_bezier2(c, b2, a3, p4, _vx_bezier2(p1, a1, b1, c, concat(pts, [p])));
+    _vx_bezier2(c, b2, a3, p4, _vx_bezier2(p1, a1, b1, c, [each pts, p]));
 
 function _vx_bezier2(p1, p2, p3, p4, pts) =
     (abs(p1[0] - p4[0]) < 0.5 && abs(p1[1] - p4[1]) < 0.5) ? 

src/voxel/_impl/_vx_circle_impl.scad

@@ -39,10 +39,7 @@ function _vx_circle_impl(radius, filled) =
     )
     concat(
         filled ? 
-            concat(
+            [[0, radius], [0, -radius], each [for(xi = -radius; xi <= radius; xi = xi + 1) [xi, 0]]]
-                [[0, radius], [0, -radius]],
-                [for(xi = -radius; xi <= radius; xi = xi + 1) [xi, 0]]
-            )
             : 
             [
                 [0, -radius],                

src/voxel/_impl/_vx_contour_impl.scad

@@ -29,7 +29,4 @@ function _vx_contour_travel(pts, p, fst) =
         dir_i = _vx_contour_dir(_vx_contour_corner_value(pts, p[0], p[1])),
         nxt_p = p + _vx_contour_nxt_offset[dir_i]
     )
-    nxt_p == fst ? [p] :
+    nxt_p == fst ? [p] : [p, each _vx_contour_travel(pts, nxt_p, fst)];
-    concat(
-        [p], _vx_contour_travel(pts, nxt_p, fst)
-    );

src/voxel/_impl/_vx_line_impl.scad

@@ -26,9 +26,9 @@ function _vx_line_xdominant(start, end, a, s) =
         zd = az - shrx,
         endx = end[0]
     )
-    concat(
+    [
-        [start], 
+        start,
-        _vx_line_xdominant_sub(
+        each _vx_line_xdominant_sub(
             x + sx, 
             _vx_line_xdominant_y(y, yd, sy), 
             _vx_line_xdominant_z(z, zd, sz), 
@@ -38,7 +38,7 @@ function _vx_line_xdominant(start, end, a, s) =
             _vx_line_xdominant_yd(yd, ax, ay), 
             _vx_line_xdominant_zd(zd, ax, az)
         )
-    );
+    ];
 
 function _vx_line_xdominant_sub(x, y, z, endx, a, s, yd, zd) = 
     let(
@@ -49,19 +49,19 @@ function _vx_line_xdominant_sub(x, y, z, endx, a, s, yd, zd) =
         sy = s[1],
         sz = s[2]
     )
-    x == endx ? [] : 
+    x == endx ? [] : [
-        concat([[x, y, z]], 
+        [x, y, z], 
-            _vx_line_xdominant_sub(
+        each _vx_line_xdominant_sub(
-                x + sx, 
+            x + sx, 
-                _vx_line_xdominant_y(y, yd, sy), 
+            _vx_line_xdominant_y(y, yd, sy), 
-                _vx_line_xdominant_z(z, zd, sz), 
+            _vx_line_xdominant_z(z, zd, sz), 
-                endx, 
+            endx, 
-                a, 
+            a, 
-                s, 
+            s, 
-                _vx_line_xdominant_yd(yd, ax, ay), 
+            _vx_line_xdominant_yd(yd, ax, ay), 
-                _vx_line_xdominant_zd(zd, ax, az)
+            _vx_line_xdominant_zd(zd, ax, az)
-            )
+        )
-        );
+    ];
         
 // y-dominant
 function _vx_line_ydominant_x(x, xd, sx) = xd >= 0 ? x + sx : x;
@@ -85,9 +85,9 @@ function _vx_line_ydominant(start, end, a, s) =
         zd = az - shry,
         endy = end[1]
     )
-    concat(
+    [
-        [start], 
+        start,
-        _vx_line_ydominant_sub(
+        each _vx_line_ydominant_sub(
             _vx_line_ydominant_x(x, xd, sx), 
             y + sy,
             _vx_line_ydominant_z(z, zd, sz), 
@@ -97,7 +97,7 @@ function _vx_line_ydominant(start, end, a, s) =
             _vx_line_ydominant_xd(xd, ax, ay), 
             _vx_line_ydominant_zd(zd, ay, az)
         )
-    );
+    ];
 
 function _vx_line_ydominant_sub(x, y, z, endy, a, s, xd, zd) = 
     let(
@@ -108,19 +108,19 @@ function _vx_line_ydominant_sub(x, y, z, endy, a, s, xd, zd) =
         sy = s[1],
         sz = s[2]
     )
-    y == endy ? [] : 
+    y == endy ? [] : [
-        concat([[x, y, z]], 
+        [x, y, z],
-            _vx_line_ydominant_sub(
+        each _vx_line_ydominant_sub(
-                _vx_line_ydominant_x(x, xd, sx), 
+            _vx_line_ydominant_x(x, xd, sx), 
-                y + sy,
+            y + sy,
-                _vx_line_ydominant_z(z, zd, sz), 
+            _vx_line_ydominant_z(z, zd, sz), 
-                endy, 
+            endy, 
-                a, 
+            a, 
-                s, 
+            s, 
-                _vx_line_ydominant_xd(xd, ax, ay), 
+            _vx_line_ydominant_xd(xd, ax, ay), 
-                _vx_line_ydominant_zd(zd, ay, az)
+            _vx_line_ydominant_zd(zd, ay, az)
-            )
+        )
-        );
+    ];
 
 // z-dominant
 function _vx_line_zdominant_x(x, xd, sx) = xd >= 0 ? x + sx : x;
@@ -145,9 +145,9 @@ function _vx_line_zdominant(start, end, a, s) =
         yd = ay - shrz,
         endz = end[2]
     )
-    concat(
+    [
-        [start], 
+        start, 
-        _vx_line_zdominant_sub(
+        each _vx_line_zdominant_sub(
             _vx_line_zdominant_x(x, xd, sx), 
             _vx_line_zdominant_y(y, yd, sy), 
             z + sz,
@@ -157,7 +157,7 @@ function _vx_line_zdominant(start, end, a, s) =
             _vx_line_zdominant_xd(xd, ax, az), 
             _vx_line_zdominant_yd(yd, ay, az)
         )
-    );
+    ];
 
 function _vx_line_zdominant_sub(x, y, z, endz, a, s, xd, yd) = 
     let(
@@ -168,20 +168,20 @@ function _vx_line_zdominant_sub(x, y, z, endz, a, s, xd, yd) =
         sy = s[1],
         sz = s[2]
     )
-    z == endz ? [] : 
+    z == endz ? [] : [
-        concat([[x, y, z]], 
+        [x, y, z],
-            _vx_line_zdominant_sub(
+        each _vx_line_zdominant_sub(
-                _vx_line_zdominant_x(x, xd, sx), 
+            _vx_line_zdominant_x(x, xd, sx), 
-                _vx_line_zdominant_y(y, yd, sy), 
+            _vx_line_zdominant_y(y, yd, sy), 
-                z + sz,
+            z + sz,
-                endz, 
+            endz, 
-                a, 
+            a, 
-                s, 
+            s, 
-                _vx_line_zdominant_xd(xd, ax, az), 
+            _vx_line_zdominant_xd(xd, ax, az), 
-                _vx_line_zdominant_yd(yd, ay, az)
+            _vx_line_zdominant_yd(yd, ay, az)
-            )
+        )
-        );
+    ];
-        
+
 function _vx_line_impl(p1, p2) = 
     let(
         is_2d = len(p1) == 2,

src/voxel/vx_curve.scad

@@ -14,15 +14,15 @@ use <../util/dedup.scad>;
 function vx_curve(points, tightness = 0) = 
     let(
         leng = len(points),
-        pts = concat(
+        pts = [
-            [
+            each [
                 for(i = [0:leng - 4])
                     let(
                         pts = _vx_catmull_rom_spline_4pts([for(j = [i:i + 3]) points[j]], tightness)
                     )
                     for(i = [0:len(pts) - 2]) pts[i]    
             ],
-            [points[leng - 2]]
+            points[leng - 2]
-        )
+        ]
     )
     dedup(pts);

src/voxel/vx_polygon.scad

@@ -4,7 +4,7 @@ use <../util/dedup.scad>;
 use <vx_polyline.scad>;
 
 function vx_polygon(points, filled = false) =
-    let(contour = vx_polyline(concat(points, [points[0]])))
+    let(contour = vx_polyline([each points, points[0]]))
     !filled ? contour :
     let(
         sortedXY = sort(contour, by = "vt"),