by supports a function literal

README.md

@@ -139,7 +139,7 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 - [util/parse_number](https://openhome.cc/eGossip/OpenSCAD/lib2x-parse_number.html)
 - [util/reverse](https://openhome.cc/eGossip/OpenSCAD/lib2x-reverse.html)
 - [util/slice](https://openhome.cc/eGossip/OpenSCAD/lib2x-slice.html)
-- [util/sort](https://openhome.cc/eGossip/OpenSCAD/lib2x-sort.html)
+- [util/sort](https://openhome.cc/eGossip/OpenSCAD/lib3x-sort.html)
 - [util/rand](https://openhome.cc/eGossip/OpenSCAD/lib2x-rand.html)
 - [util/fibseq](https://openhome.cc/eGossip/OpenSCAD/lib2x-fibseq.html)	
 - [util/bsearch](https://openhome.cc/eGossip/OpenSCAD/lib2x-bsearch.html)	

docs/lib3x-sort.md

@@ -2,14 +2,12 @@
 
 Sorts the elements of a list in ascending order. The list is a list-of-list construct, such as `[[a0, a1, a2...], [b0, b1, b2,...], [c0, c1, c2,...],...]`. When sorting, the function looks only at one index position of each sublist. 
 
-From dotSCAD 2.3, when `by` is `"vt"`, it will sort points by zyx (from the last index to the first one).
-
 **Since:** 2.0
 
 ## Parameters
 
 - `lt` : The original list.
-- `by` : Can be `"x"`、`"y"`、`"z"`, `"idx"` (Default) or `"vt"`. 
+- `by` : Can be `"x"`、`"y"`、`"z"`, or `"idx"` (Default). `"vt"`. From dotSCAD 2.3, when `by` is `"vt"`, it will sort points by zyx (from the last index to the first one). From dotSCAD 3.0, `by` supports a function literal that compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
 - `idx` : When `by` is `"idx"`, the value of `idx` is used. The Default value is 0.
 
 ## Examples
@@ -29,4 +27,9 @@ From dotSCAD 2.3, when `by` is `"vt"`, it will sort points by zyx (from the last
     assert(
         [[0, 2, 0], [0, 5, 0], [0, 7, 0], [0, 9, 0], [0, 10, 0]] == 
         sort([[0, 10, 0], [0, 5, 0], [0, 7, 0], [0, 2, 0], [0, 9, 0]], by = "idx", idx = 1)
-    );
+    );
+
+    ascending = function(e1, e2) e1 - e2;
+    descending = function(e1, e2) e2 - e1;
+    assert(sort([2, 1, 3, 5, 4], by = ascending) == [1, 2, 3, 4, 5]);
+    assert(sort([2, 1, 3, 5, 4], by = descending) == [5, 4, 3, 2, 1]);

src/util/_impl/_sort_impl.scad

@@ -25,4 +25,14 @@ function _sort_by(lt, by, idx) =
         dict = [["x", 0], ["y", 1], ["z", 2], ["i", idx]],
         i = dict[search(by == "idx" ? "i" : by, dict)[0]][1]
     )
-    _sort_by_idx(lt, i);
+    _sort_by_idx(lt, i);
+
+function _sort_by_comp(lt, comp) = 
+    let(leng = len(lt))
+    leng <= 1 ? lt : 
+        let(
+            pivot = lt[0],
+            before = [for(j = 1; j < leng; j = j + 1) if(comp(lt[j], pivot) < 0) lt[j]],
+            after =  [for(j = 1; j < leng; j = j + 1) if(comp(lt[j], pivot) >= 0) lt[j]]
+        )
+        concat(_sort_by_comp(before, comp), [pivot], _sort_by_comp(after, comp));

src/util/sort.scad

@@ -4,12 +4,13 @@
 * @copyright Justin Lin, 2019
 * @license https://opensource.org/licenses/lgpl-3.0.html
 *
-* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-sort.html
+* @see https://openhome.cc/eGossip/OpenSCAD/lib3x-sort.html
 *
 **/ 
 
 use <_impl/_sort_impl.scad>;
 
 function sort(lt, by = "idx", idx = 0) = 
+    is_function(by) ? _sort_by_comp(lt, by) :  // support function literal
     by == "vt" ? _vt_sort(lt) :      // for example, sort by zyx for a list of points
                  _sort_by(lt, by, idx);

test/util/test_sort.scad

@@ -4,20 +4,25 @@ use <util/sort.scad>;
 module test_sort() {
     echo("==== test_sort ====");
 
-    assertEqualPoints(
-        [[2, 0, 0], [5, 0, 0], [7, 0, 0], [9, 0, 0], [10, 0, 0]], 
+    assert(
+        [[2, 0, 0], [5, 0, 0], [7, 0, 0], [9, 0, 0], [10, 0, 0]] == 
+        sort([[10, 0, 0], [5, 0, 0], [7, 0, 0], [2, 0, 0], [9, 0, 0]])
+    );
+
+    assert(
+        [[2, 0, 0], [5, 0, 0], [7, 0, 0], [9, 0, 0], [10, 0, 0]] == 
         sort([[10, 0, 0], [5, 0, 0], [7, 0, 0], [2, 0, 0], [9, 0, 0]], by = "x")
     );
 
-    assertEqualPoints(
-        [[2, 0, 0], [5, 0, 0], [7, 0, 0], [9, 0, 0], [10, 0, 0]], 
-        sort([[10, 0, 0], [5, 0, 0], [7, 0, 0], [2, 0, 0], [9, 0, 0]], by = "idx", idx = 0)
-    );
-
-    assertEqualPoints(
-        [[0, 2, 0], [0, 5, 0], [0, 7, 0], [0, 9, 0], [0, 10, 0]], 
-        sort([[0, 10, 0], [0, 5, 0], [0, 7, 0], [0, 2, 0], [0, 9, 0]], by = "y")
+    assert(
+        [[0, 2, 0], [0, 5, 0], [0, 7, 0], [0, 9, 0], [0, 10, 0]] == 
+        sort([[0, 10, 0], [0, 5, 0], [0, 7, 0], [0, 2, 0], [0, 9, 0]], by = "idx", idx = 1)
     );
+ 
+    ascending = function(e1, e2) e1 - e2;
+    descending = function(e1, e2) e2 - e1;
+    assert(sort([2, 1, 3, 5, 4], by = ascending) == [1, 2, 3, 4, 5]);
+    assert(sort([2, 1, 3, 5, 4], by = descending) == [5, 4, 3, 2, 1]);
 }
 
 test_sort();