Expressed `Take` and `Drop` in terms of new `Section` operation

* unifies the common functionality between `Take` and `Drop`
* renamed `basic.h` to `length.h` as it only contains the `Length` implementation

1 files changed, 76 insertions, 0 deletions

diff --git a/src/list/operation/section.h b/src/list/operation/section.h
new file mode 100644
index 0000000..214c9fd
--- /dev/null
+++ b/src/list/operation/section.h
@@ -0,0 +1,76 @@
+#ifndef TYPEASVALUE_SRC_LIST_OPERATION_SECTION_H_
+#define TYPEASVALUE_SRC_LIST_OPERATION_SECTION_H_
+
+#include "operation/math.h"
+
+namespace tav {
+
+namespace detail {
+
+template <
+	typename Index,
+	typename Count,
+	typename List
+>
+struct take_count_at {
+	typedef Eval<take_count_at<
+		Substract<Index, Size<1>>,
+		Count,
+		Tail<List>
+	>> type;
+};
+
+template <
+	typename Count,
+	typename List
+>
+struct take_count_at<Size<0>, Count, List> {
+	typedef Cons<
+		Head<List>,
+		Eval<take_count_at<
+			Size<0>,
+			Substract<Count, Size<1>>,
+			Tail<List>
+		>>
+	> type;
+};
+
+template <
+	typename Index,
+	typename Count
+>
+struct take_count_at<Index, Count, void> {
+	typedef void type;
+};
+
+template <typename Count>
+struct take_count_at<Size<0>, Count, void> {
+	typedef void type;
+};
+
+template <typename List>
+struct take_count_at<Size<0>, Size<0>, List> {
+	typedef void type;
+};
+
+template <>
+struct take_count_at<Size<0>, Size<0>, void> {
+	typedef void type;
+};
+
+}
+
+template <
+	typename Start,
+	typename End,
+	typename List
+>
+using Section = Eval<detail::take_count_at<
+	Start,
+	Substract<Add<End, Size<1>>, Start>,
+	List
+>>;
+
+}
+
+#endif  // TYPEASVALUE_SRC_LIST_OPERATION_SECTION_H_