diff --git a/include/Rivet/Tools/RivetSTL.hh b/include/Rivet/Tools/RivetSTL.hh
--- a/include/Rivet/Tools/RivetSTL.hh
+++ b/include/Rivet/Tools/RivetSTL.hh
@@ -1,196 +1,196 @@
 #ifndef RIVET_RivetSTL_HH
 #define RIVET_RivetSTL_HH
 
 #include <string>
 #include <array>
 #include <vector>
 #include <list>
 #include <set>
 #include <map>
 
 #include <memory>
-
+#include <functional>
 
 // #include <utility>
 // #include <tuple>
 // #include <algorithm>
 // #include <cassert>
 // #include <typeinfo>
 
 // #include <iomanip>
 // #include <cmath>
 // #include <limits>
 
 #include <ostream>
 #include <sstream>
 
 namespace Rivet {
 
 
   /// We implicitly use STL entities in the Rivet namespace
   // using namespace std;
   using std::string;
   using std::to_string;
 
   using std::array;
   using std::vector;
   using std::list;
   using std::set;
   using std::multiset;
   using std::map;
   using std::multimap;
   using std::pair;
   using std::make_pair;
 
   using std::unique_ptr;
   using std::shared_ptr;
   using std::make_shared;
   using std::dynamic_pointer_cast;
 
   using std::initializer_list;
 
   using std::function;
 
   /// @name Streaming containers as string reps
   /// @todo Make these named toStr rather than operator<<
   /// @todo Make these generic to any iterable
   //@{
 
   /// Convenient function for streaming out vectors of any streamable object.
   template<typename T>
   inline std::ostream& operator<<(std::ostream& os, const std::vector<T>& vec) {
     os << "[ ";
     for (size_t i=0; i<vec.size(); ++i) {
       os << vec[i] << " ";
     }
     os << "]";
     return os;
   }
 
   /// Convenient function for streaming out lists of any streamable object.
   template<typename T>
   inline std::ostream& operator<<(std::ostream& os, const std::list<T>& vec) {
     os << "[ ";
     for (size_t i=0; i<vec.size(); ++i) {
       os << vec[i] << " ";
     }
     os << "]";
     return os;
   }
 
   //@}
 
 
   /// @name Boolean-return container searching
   //@{
 
   /// @todo Use SFINAE, Boost.Range, or other template trickery for more generic container matching?
 
   /// Does @a s contain @a sub as a substring?
   inline bool contains(const std::string& s, const std::string& sub) {
     return s.find(sub) != string::npos;
   }
 
   /// Does the init list @a il contain @a x?
   template <typename T>
   inline bool contains(const std::initializer_list<T>& il, const T& x) {
     return find(begin(il), end(il), x) != end(il);
   }
 
   /// Does the vector @a v contain @a x?
   template <typename T>
   inline bool contains(const std::vector<T>& v, const T& x) {
     return find(begin(v), end(v), x) != end(v);
   }
 
   /// Does the list @a l contain @a x?
   template <typename T>
   inline bool contains(const std::list<T>& l, const T& x) {
     return find(begin(l), end(l), x) != end(l);
   }
 
   /// Does the set @a s contain @a x?
   template <typename T>
   inline bool contains(const std::set<T>& s, const T& x) {
     return find(begin(s), end(s), x) != end(s);
   }
 
   /// Does the map @a m contain the key @a key?
   template <typename K, typename T>
   inline bool has_key(const std::map<K, T>& m, const K& key) {
     return m.find(key) != end(m);
   }
 
   /// Does the map @a m contain the value @a val?
   template <typename K, typename T>
   inline bool has_value(const std::map<K, T>& m, const T& val) {
     for (typename std::map<K,T>::const_iterator it = begin(m); it != end(m); ++it) {
       if (it->second == val) return true;
     }
     return false;
   }
 
   //@}
 
 
 }
 
 namespace std {
 
 
   /// @name Container filling and merging
   //@{
 
   /// Append a single item to vector @a v
   template <typename T>
   inline void operator+=(std::vector<T>& v, const T& x) { v.push_back(x); }
 
   /// Append all the items from vector @a v2 to vector @a v1
   template <typename T>
   inline void operator+=(std::vector<T>& v1, const std::vector<T>& v2) {
     for (const auto& x : v2) v1.push_back(x);
   }
 
   /// Create a new vector from the concatenated items in vectors @a v1 and @a v2
   template <typename T>
   inline std::vector<T> operator+(const std::vector<T>& v1, const std::vector<T>& v2) {
     std::vector<T> rtn(v1);
     rtn += v2;
     return rtn;
   }
 
 
   /// Merge the contents of set @a s2 into @a s1
   template <typename T>
   inline void operator+=(std::set<T>& s1, const std::set<T>& s2) {
     for (const auto& x : s2) s1.insert(x);
   }
 
   /// Merge the contents of sets @a s1 and @a s2
   template <typename T>
   inline std::set<T> operator+(const std::set<T>& s1, const std::set<T>& s2) {
     std::set<T> rtn(s1);
     rtn += s2;
     return rtn;
   }
 
   //@}
 
 
   /// @name Function helpers
   //@{
 
   /// Get a function pointer / hash integer from an std::function
   template<typename T, typename... U>
   inline size_t get_address(std::function<T(U...)> f) {
     typedef T(fnType)(U...);
     fnType ** fnPointer = f.template target<fnType*>();
     return (fnPointer != nullptr) ? reinterpret_cast<size_t>(*fnPointer) : 0;
   }
 
   //@}
 
 
 }
 
 #endif