create symbol from nodeattr (#116)

nnvm/include/nnvm/symbolic.h

@@ -21,7 +21,7 @@
 namespace nnvm {
 /*!
  * \brief Symbol is help class used to represent the operator node in Graph.
- * 
+ *
  *  Symbol acts as an interface for building graphs from different components
  *  like Variable, Functor and Group. Symbol is also exported to python front-end
  *  (while Graph is not) to enable quick test and deployment. Conceptually,
@@ -193,6 +193,12 @@ class Symbol {
   static Symbol CreateFunctor(const Op* op,
                               std::unordered_map<std::string, std::string> attrs);
   /*!
+   * \brief Create symbolic functor(AtomicSymbol) by given node attributes.
+   * \param attrs pre-initialized Node attributes.
+   * \return Symbol that can be used to call compose further.
+   */
+  static Symbol CreateFunctor(const NodeAttrs& attrs);
+  /*!
    * \brief Create symbol node representing variable.
    * \param name Name of the variable.
    * \return The symbol.

nnvm/src/core/symbolic.cc

@@ -527,6 +527,22 @@ Symbol Symbol::CreateFunctor(const Op* op,
   return s;
 }
 
+Symbol Symbol::CreateFunctor(const NodeAttrs& attrs) {
+  static auto& fnum_vis_output = Op::GetAttr<FNumVisibleOutputs>("FNumVisibleOutputs");
+  Symbol s;
+  NodePtr n = Node::Create();
+  n->attrs = attrs;
+
+  uint32_t nout = n->num_outputs();
+  if (fnum_vis_output.count(n->op())) {
+    nout = fnum_vis_output[n->op()](n->attrs);
+  }
+  for (uint32_t i = 0; i < nout; ++i) {
+    s.outputs.emplace_back(NodeEntry{n, i, 0});
+  }
+  return s;
+}
+
 Symbol Symbol::CreateGroup(const std::vector<Symbol> &symbols) {
   Symbol ret;
   for (const auto &s : symbols) {