Add begin/end functions for instruction stream

include/rtg/program.hpp

@@ -52,6 +52,9 @@ struct program
 
     bool has_instruction(instruction_ref ins) const;
 
+    instruction_ref begin();
+    instruction_ref end();
+
     private:
     std::unique_ptr<program_impl> impl;
 };

src/program.cpp

@@ -59,6 +59,15 @@ bool program::has_instruction(instruction_ref ins) const
                }) != impl->instructions.end();
 }
 
+instruction_ref program::begin()
+{
+    return impl->instructions.begin();
+}
+instruction_ref program::end()
+{
+    return impl->instructions.end();
+}
+
 literal program::eval(std::unordered_map<std::string, argument> params) const
 {
     std::unordered_map<const instruction*, argument> results;