Initial data commit

Task/Sorting-algorithms-Shell-sort/Icon/sorting-algorithms-shell-sort.icon

@@ -0,0 +1,21 @@
+procedure main()                     #: demonstrate various ways to sort a list and string
+   demosort(shellsort,[3, 14, 1, 5, 9, 2, 6, 3],"qwerty")
+end
+
+procedure shellsort(X,op)             #: return sorted X
+local i,j,inc,temp
+
+   op := sortop(op,X)                 # select how and what we sort
+
+   inc := *X/2
+   while inc > 0 do {
+      every i := inc to *X do {
+         temp := X[j := i]
+         while op(temp,X[j - (j >= inc)]) do
+            X[j] := X[j -:= inc]
+         X[j] := temp
+         }
+      inc := if inc = 2 then 1 else inc*5/11 # switch to insertion near the end
+      }
+   return X
+end