Add missing has_op function (#704)

* Add missing has_op function

* Formatting

src/register_op.cpp

@@ -16,6 +16,8 @@ operation load_op(const std::string& name)
     return at(op_map(), name, "Operator not found: " + name);
 }
 
+bool has_op(const std::string& name) { return op_map().count(name) == 1; }
+
 std::vector<std::string> get_operators()
 {
     std::vector<std::string> result;