Improve params.register() (#747)

* Drop callback.

This is only used by daipp. This will be addressed later.

* Assume that getParams returns unlifted values.

* Rename variable.

* Move ad.lift outside of conditional.

* Only lift parameters when doing optimization.

* Improve commentary.

* Better name for function parameter.

src/params/params.js

@@ -1,5 +1,6 @@
 'use strict';
 
+var assert = require('assert');
 var _ = require('lodash');
 var fs = require('fs');
 var ad = require('../ad');
@@ -72,55 +73,45 @@ function set(params, k) {
 }
 
 
-function register(env, name, getParams, setParams) {
-
-  // getParams is expected to be a function which is used to
-  // initialize parameters the first time they are encoutered. At
-  // present I consider it to be `register` responsibility to
-  // perform lifting of params, so ideally `getParams` would not
-  // return lifted params. However, in the case of NN, `getParams`
-  // returns params already lifted. Hence, `getParams()` is replaced
-  // with `getParams().map(ad.value)` throughout this function.
+function register(env, name, initParams) {
 
   var paramTable = get();
   var paramsSeen = env.coroutine.paramsSeen;
 
   if (paramsSeen && _.has(paramsSeen, name)) {
 
-    // We've already lifted these params during this execution.
+    // We've already lifted these parameters during this execution.
     // Re-use ad graph nodes.
 
     return paramsSeen[name];
 
   } else {
 
-    // This is the first time we've encounter these params during
-    // this execution. we will lift params at this point.
-
-    var params;
-
+    // Get parameter values from the store, or initialize if this is a
+    // new parameter.
+    var _params;
     if (_.has(paramTable, name)) {
-      // Seen on previous execution. Fetch from store and lift.
-      params = paramTable[name].map(ad.lift);
+      // Parameters already initialized. Fetch values from store.
+      _params = paramTable[name];
     } else {
-      // Never seen. Fetch initial values, add to store and lift.
-      var prms = getParams().map(ad.value);
-      paramTable[name] = prms;
-      params = prms.map(ad.lift);
+      // Never seen. Fetch initial values and add to store.
+      _params = initParams();
+      assert.ok(_.every(_params, _.negate(ad.isLifted)),
+                'initParams unexpectedly returned a lifted value.');
+      paramTable[name] = _params;
     }
 
     if (paramsSeen) {
+      // Lift parameters if the current coroutine is tracking
+      // parameters for optimization.
+      var params = _params.map(ad.lift);
       paramsSeen[name] = params;
+      return params;
+    } else {
+      return _params;
     }
 
-    // Callback with the fresh ad graph nodes.
-    if (setParams) {
-      setParams(params);
-    }
-
-    return params;
   }
-
 }