reorganize directory and file structure

lib/structures/set.js

@@ -0,0 +1,29 @@
+import { newRight } from "./sum.js";
+import { newProduct } from "./product.js";
+import { unit } from "../primitives/unit.js";
+import { RBTreeWrapper } from "../util/rbtree_wrapper.js";
+
+// (a -> a -> Int) -> Set(a)
+export const emptySet = compareFn => RBTreeWrapper.new((x, y) => compareFn(x)(y));
+
+export const has = set => key => set.tree.get(key) === true;
+export const add = set => key => set.tree.get(key) === true ? set : new RBTreeWrapper(set.tree.insert(key, true));
+export const remove = set => key => new RBTreeWrapper(set.tree.remove(key));
+export const length = set => set.tree.length;
+
+export const first = set => set.tree.begin;
+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()));
+  }
+  else {
+    return newLeft(unit);
+  }
+};
+
+export const forEach = set => fn => {
+  set.tree.forEach(key => { fn(key); });
+};