Implemented `Take` function

* as its name implies this function _takes_ a maximum of _Count_ elements of a list
* added appropriate test case

2 files changed, 43 insertions, 1 deletions

diff --git a/src/list/operation/basic.h b/src/list/operation/basic.h
index cee4cbc..dbd080e 100644
--- a/src/list/operation/basic.h
+++ b/src/list/operation/basic.h
@@ -2,6 +2,7 @@
 #define TYPEASVALUE_SRC_LIST_OPERATION_BASIC_H_
 
 #include "operation/math.h"
+#include "conditional/if.h"
 
 namespace tav {
 
@@ -26,7 +27,10 @@ struct Nth {
 	typedef If<
 		equal_value<Index, Size<0>>::value,
 		Head<Cons>,
-		typename Nth<Substract<Index, Size<1>>, Tail<Cons>>::type
+		typename Nth<
+			Substract<Index, Size<1>>,
+			Tail<Cons>
+		>::type
 	> type;
 };
 
@@ -35,6 +39,35 @@ struct Nth<Index, void> {
 	typedef void type;
 };
 
+template <
+	typename Count,
+	typename Current
+>
+struct Take {
+	typedef Cons<
+		Head<Current>,
+		typename Take<
+			Substract<Count, Size<1>>,
+			Tail<Current>
+		>::type
+	> type;
+};
+
+template <typename Current>
+struct Take<Size<0>, Current> {
+	typedef void type;
+};
+
+template <typename Count>
+struct Take<Count, void> {
+	typedef void type;
+};
+
+template <>
+struct Take<Size<0>, void> {
+	typedef void type;
+};
+
 }
 
 #endif  // TYPEASVALUE_SRC_LIST_OPERATION_BASIC_H_
diff --git a/test.cc b/test.cc
index e8f7c47..f60adbd 100644
--- a/test.cc
+++ b/test.cc
@@ -62,6 +62,15 @@ TEST_F(TypeAsValueTest, ListNth) {
 	EXPECT_EQ(2, ( tav::Nth<tav::Size<1>, tav::List<tav::Int<1>, tav::Int<2>>::type>::type::value ));
 }
 
+TEST_F(TypeAsValueTest, ListTake) {
+	// (length (take 1 (list 1 2)))
+	EXPECT_EQ(1, ( tav::Length<tav::Take<tav::Size<1>, tav::List<tav::Int<1>, tav::Int<2>>::type>::type>::type::value ));
+	// (length (take 2 (list 1 2)))
+	EXPECT_EQ(2, ( tav::Length<tav::Take<tav::Size<2>, tav::List<tav::Int<1>, tav::Int<2>>::type>::type>::type::value ));
+	// (length (take 3 (list 1 2)))
+	EXPECT_EQ(2, ( tav::Length<tav::Take<tav::Size<3>, tav::List<tav::Int<1>, tav::Int<2>>::type>::type>::type::value ));
+}
+
 TEST_F(TypeAsValueTest, ListConcatenate) {
 	// (length (concatenate (list 1) (list 2)))
 	EXPECT_EQ(2, ( tav::Length<tav::Concatenate<tav::List<tav::Int<1>>::type, tav::List<tav::Int<2>>::type>::type>::type::value ));