Another update from ingydotnet^djgoku

Task/Sorting-algorithms-Quicksort/Fexl/sorting-algorithms-quicksort.fexl

@@ -1,15 +1,18 @@
-# (sort keep compare xs) sorts the list xs using the three-way comparison
-# function.  It keeps duplicates if the keep flag is true, otherwise it
-# discards them and returns only the unique entries.
-
-\sort ==
-    (\keep\compare\xs
-    xs end \x\xs
-
-    \lo = (filter (\y compare y x T F F) xs)
-    \hi = (filter (\y compare y x F keep T) xs)
-
-    append (sort keep compare lo);
-    item x;
-    sort keep compare hi
+# (sort xs) is the ordered list of all elements in list xs.
+# This version preserves duplicates.
+\sort==
+    (\xs
+    xs [] \x\xs
+    append (sort; filter (gt x) xs);   # all the items less than x
+    cons x; append (filter (eq x) xs); # all the items equal to x
+    sort; filter (lt x) xs             # all the items greater than x
+    )
+
+# (unique xs) is the ordered list of unique elements in list xs.
+\unique==
+    (\xs
+    xs [] \x\xs
+    append (unique; filter (gt x) xs); # all the items less than x
+    cons x;                            # x itself
+    unique; filter (lt x) xs           # all the items greater than x
     )