Implemented `Count` in terms of `Fold` and `Map`

* as its name implies this function counts the amount of elements satisfying a given _function_
* added appropriate test case

1 files changed, 11 insertions, 0 deletions

diff --git a/src/list/operation/higher/query.h b/src/list/operation/higher/query.h
index 29f65dc..c6eabc7 100644
--- a/src/list/operation/higher/query.h
+++ b/src/list/operation/higher/query.h
@@ -3,6 +3,7 @@
 
 #include "fold.h"
 #include "misc.h"
+#include "operation/math.h"
 #include "operation/logic.h"
 
 namespace tav {
@@ -35,6 +36,16 @@ using None = Not<
 	typename Any<Function, List>::type
 >;
 
+template <
+	template<typename> class Function,
+	typename                 List
+>
+using Count = Fold<
+	Add,
+	tav::Size<0>,
+	typename Map<Function, List>::type
+>;
+
 }
 
 #endif  // TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_QUERY_H_