add dict comparison function

lib/structures/set.js

@@ -17,7 +17,11 @@ export const last  = set => set.tree.end;
 // test if iterator is 'done', and if not, get element and advance iterator.
 export const read = iter => {
   if (iter !== undefined && iter.valid) {
-    return newRight(newProduct(iter.key)(iter.clone().next()));
+    return newRight(
+      newProduct
+        (iter.key)
+        (iter.clone().next())
+    );
   }
   else {
     return newLeft(unit);