initial attempt to add+export E() wrapper

No tests yet. Requires the addition of `@agoric/harden` as a dependency.

refs Agoric#30

package.json

@@ -22,7 +22,9 @@
     "url": "https://github.com/Agoric/eventual-send/issues"
   },
   "homepage": "https://github.com/Agoric/eventual-send#readme",
-  "dependencies": {},
+  "dependencies": {
+    "@agoric/harden": "^0.0.4"
+  },
   "devDependencies": {
     "eslint": "^5.3.0",
     "eslint-config-airbnb": "^17.1.0",

src/E.js

@@ -0,0 +1,57 @@
+import harden from '@agoric/harden';
+
+/**
+ * A Proxy handler for E(x).
+ *
+ * @param {Promise} ep Promise with eventual send API
+ * @returns {ProxyHandler} the Proxy handler
+ */
+function EPromiseHandler(ep) {
+  return harden({
+    get(_target, p, _receiver) {
+      if (`${p}` !== p) {
+        return undefined;
+      }
+      // Harden this Promise because it's our only opportunity to ensure
+      // p1=E(x).foo() is hardened. The Handled Promise API does not (yet)
+      // allow the handler to synchronously influence the promise returned
+      // by the handled methods, so we must freeze it from the outside. See
+      // #95 for details.
+      return (...args) => harden(ep.post(p, args));
+    },
+    deleteProperty(_target, p) {
+      return harden(ep.delete(p));
+    },
+    set(_target, p, value, _receiver) {
+      return harden(ep.put(p, value));
+    },
+    apply(_target, _thisArg, argArray = []) {
+      return harden(ep.post(undefined, argArray));
+    },
+    has(_target, _p) {
+      // We just pretend everything exists.
+      return true;
+    },
+  });
+}
+
+export default function E(x) {
+  // p = E(x).name(args)
+  //
+  // E(x) returns a proxy on which you can call arbitrary methods. Each of
+  // these method calls returns a promise. The method will be invoked on
+  // whatever 'x' designates (or resolves to) in a future turn, not this
+  // one.
+
+  const targetP = Promise.resolve(x);
+  // targetP might resolve to a Presence
+  const handler = EPromiseHandler(targetP);
+  return harden(new Proxy({}, handler));
+}
+
+// Like Promise.resolve, except that if applied to a presence, it
+// would be better for it to return the remote promise for this
+// specimen, rather than a fresh local promise fulfilled by this
+// specimen.
+// TODO: for now, just alias Promise.resolve.
+E.resolve = specimen => Promise.resolve(specimen);

src/index.js

@@ -1,3 +1,7 @@
+import E from './E';
+
+export { E };
+
 // Create HandledPromise static methods as a bridge from v0.2.4 to
 // new proposal support (wavy dot's infrastructure).
 export function makeHandledPromise(EPromise) {