unique_append now returns the number of unique elements appended

misc.go

@@ -16,12 +16,14 @@ func assert(cond bool) {
 }
 
 // Ensure that the given elements are only appended to the given slice if they
-// don't already exist.
-func unique_append[T comparable](slc []T, items ...T) []T {
+// don't already exist. Returns the new slice, and the number of unique items appended.
+func unique_append[T comparable](slc []T, items ...T) ([]T, int) {
+	num_appended := 0
 	for _, item := range items {
 		if !slices.Contains(slc, item) {
 			slc = append(slc, item)
+			num_appended++
 		}
 	}
-	return slc
+	return slc, num_appended
 }