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

8 files changed, 167 insertions, 145 deletions

diff --git a/src/list/generator/higher/list_tabulate.h b/src/list/generator/higher/list_tabulate.h
index 856ed11..4ffbc02 100644
--- a/src/list/generator/higher/list_tabulate.h
+++ b/src/list/generator/higher/list_tabulate.h
@@ -12,7 +12,7 @@ template <
 >
 using ListTabulate = Map<
 	Initializer,
-	Eval<Iota<Count, Size<0>, Size<1>>>
+	Iota<Count, Size<0>, Size<1>>
 >;
 
 }
diff --git a/src/list/list.h b/src/list/list.h
index edb52ec..cf4f415 100644
--- a/src/list/list.h
+++ b/src/list/list.h
@@ -26,7 +26,7 @@ using Tail = Cdr<Cons>;
 
 }
 
-#include "operation/basic.h"
+#include "operation/length.h"
 #include "operation/nth.h"
 #include "operation/take.h"
 #include "operation/drop.h"
diff --git a/src/list/operation/drop.h b/src/list/operation/drop.h
index c7745d7..aef88d3 100644
--- a/src/list/operation/drop.h
+++ b/src/list/operation/drop.h
@@ -1,45 +1,20 @@
 #ifndef TYPEASVALUE_SRC_LIST_OPERATION_DROP_H_
 #define TYPEASVALUE_SRC_LIST_OPERATION_DROP_H_
 
-#include "operation/math.h"
+#include "length.h"
+#include "section.h"
 
 namespace tav {
 
-namespace detail {
-
-template <
-	typename Count,
-	typename Current
->
-struct Drop {
-	typedef Eval<Drop<
-		Substract<Count, Size<1>>,
-		Tail<Current>
-	>> type;
-};
-
-template <typename Current>
-struct Drop<Size<0>, Current> {
-	typedef Current type;
-};
-
-template <typename Count>
-struct Drop<Count, void> {
-	typedef void type;
-};
-
-template <>
-struct Drop<Size<0>, void> {
-	typedef void type;
-};
-
-}
-
 template <
 	typename Count,
-	typename Current
+	typename List
 >
-using Drop = Eval<detail::Drop<Count, Current>>;
+using Drop = Section<
+	Count,
+	Substract<Length<List>, Size<1>>,
+	List
+>;
 
 }
 
diff --git a/src/list/operation/higher/fold.h b/src/list/operation/higher/fold.h
index 3f39b40..38c3554 100644
--- a/src/list/operation/higher/fold.h
+++ b/src/list/operation/higher/fold.h
@@ -8,12 +8,12 @@ namespace detail {
 template <
 	template<typename, typename> class Function,
 	typename                           Initial,
-	typename                           Current
+	typename                           Pair
 >
 struct fold_pair {
 	typedef Function<
-		Head<Current>,
-		Eval<fold_pair<Function, Initial, Tail<Current>>>
+		Car<Pair>,
+		Eval<fold_pair<Function, Initial, Cdr<Pair>>>
 	> type;
 };
 
@@ -30,9 +30,9 @@ struct fold_pair<Function, Initial, void> {
 template <
 	template<typename, typename> class Function,
 	typename                           Initial,
-	typename                           Current
+	typename                           List
 >
-using Fold = Eval<detail::fold_pair<Function, Initial, Current>>;
+using Fold = Eval<detail::fold_pair<Function, Initial, List>>;
 
 }
 
diff --git a/src/list/operation/basic.h b/src/list/operation/length.h
index d0f6212..1f609d4 100644
--- a/src/list/operation/basic.h
+++ b/src/list/operation/length.h
@@ -1,5 +1,5 @@
-#ifndef TYPEASVALUE_SRC_LIST_OPERATION_BASIC_H_
-#define TYPEASVALUE_SRC_LIST_OPERATION_BASIC_H_
+#ifndef TYPEASVALUE_SRC_LIST_OPERATION_LENGTH_H_
+#define TYPEASVALUE_SRC_LIST_OPERATION_LENGTH_H_
 
 #include "higher/fold.h"
 #include "operation/math.h"
@@ -18,4 +18,4 @@ using Length = Fold<detail::length_accumulate, Size<0>, List>;
 
 }
 
-#endif  // TYPEASVALUE_SRC_LIST_OPERATION_BASIC_H_
+#endif  // TYPEASVALUE_SRC_LIST_OPERATION_LENGTH_H_
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_
diff --git a/src/list/operation/take.h b/src/list/operation/take.h
index effba33..f9aa4b0 100644
--- a/src/list/operation/take.h
+++ b/src/list/operation/take.h
@@ -1,48 +1,19 @@
 #ifndef TYPEASVALUE_SRC_LIST_OPERATION_TAKE_H_
 #define TYPEASVALUE_SRC_LIST_OPERATION_TAKE_H_
 
-#include "operation/math.h"
+#include "section.h"
 
 namespace tav {
 
-namespace detail {
-
-template <
-	typename Count,
-	typename Current
->
-struct Take {
-	typedef Cons<
-		Head<Current>,
-		Eval<Take<
-			Substract<Count, Size<1>>,
-			Tail<Current>
-		>>
-	> 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;
-};
-
-}
-
 template <
 	typename Count,
-	typename Current
+	typename List
 >
-using Take = Eval<detail::Take<Count, Current>>;
+using Take = Section<
+	Size<0>,
+	Substract<Count, Size<1>>,
+	List
+>;
 
 }
 
diff --git a/test.cc b/test.cc
index 074d711..6560795 100644
--- a/test.cc
+++ b/test.cc
@@ -359,155 +359,155 @@ static_assert(
 	"(list 1 2) != (cons 1 (cons 2 void))"
 );
 
-// list length
+// list take
 
 static_assert(
 	std::is_same<
-		tav::Size<1>,
-		tav::Length<
-			tav::List<tav::Int<1>>
+		tav::List<tav::Int<1>>,
+		tav::Take<
+			tav::Size<1>,
+			tav::List<tav::Int<1>, tav::Int<2>>
 		>
 	>::value,
-	"(length (list 1)) != 1"
+	"(take 1 (list 1 2)) != (list 1)"
 );
 
 static_assert(
 	std::is_same<
-		tav::Size<2>,
-		tav::Length<
+		tav::List<tav::Int<1>, tav::Int<2>>,
+		tav::Take<
+			tav::Size<2>,
 			tav::List<tav::Int<1>, tav::Int<2>>
 		>
 	>::value,
-	"(length (list 1 2)) != 2"
+	"(take 2 (list 1 2)) != (list 1 2)"
 );
 
-// list nth
-
 static_assert(
 	std::is_same<
-		tav::Int<1>,
-		tav::Nth<
-			tav::Size<0>,
-			tav::List<tav::Int<1>>
+		tav::List<tav::Int<1>, tav::Int<2>>,
+		tav::Take<
+			tav::Size<3>,
+			tav::List<tav::Int<1>, tav::Int<2>>
 		>
 	>::value,
-	"(nth 0 (list 1)) != 1"
+	"(take 3 (list 1 2)) != (list 1 2)"
 );
 
+// list drop
+
 static_assert(
 	std::is_same<
-		tav::Int<1>,
-		tav::Nth<
-			tav::Size<0>,
+		tav::List<tav::Int<2>>,
+		tav::Drop<
+			tav::Size<1>,
 			tav::List<tav::Int<1>, tav::Int<2>>
 		>
 	>::value,
-	"(nth 0 (list 1 2)) != 1"
+	"(drop 1 (list 1 2)) != (list 2)"
 );
 
 static_assert(
 	std::is_same<
-		tav::Int<2>,
-		tav::Nth<
-			tav::Size<1>,
+		void,
+		tav::Drop<
+			tav::Size<2>,
 			tav::List<tav::Int<1>, tav::Int<2>>
 		>
 	>::value,
-	"(nth 1 (list 1 2)) != 2"
+	"(drop 2 (list 1 2)) != void"
 );
 
 static_assert(
 	std::is_same<
-		tav::Int<1>,
-		tav::First<tav::List<tav::Int<1>, tav::Int<2>, tav::Int<3>>>
+		void,
+		tav::Drop<
+			tav::Size<3>,
+			tav::List<tav::Int<1>, tav::Int<2>>
+		>
 	>::value,
-	"(first (list 1 2 3)) != 1"
+	"(drop 3 (list 1 2)) != void"
 );
 
+// list length
+
 static_assert(
 	std::is_same<
-		tav::Int<2>,
-		tav::Second<tav::List<tav::Int<1>, tav::Int<2>, tav::Int<3>>>
+		tav::Size<1>,
+		tav::Length<
+			tav::List<tav::Int<1>>
+		>
 	>::value,
-	"(second (list 1 2 3)) != 2"
+	"(length (list 1)) != 1"
 );
 
 static_assert(
 	std::is_same<
-		tav::Int<3>,
-		tav::Third<tav::List<tav::Int<1>, tav::Int<2>, tav::Int<3>>>
+		tav::Size<2>,
+		tav::Length<
+			tav::List<tav::Int<1>, tav::Int<2>>
+		>
 	>::value,
-	"(third (list 1 2 3)) != 3"
+	"(length (list 1 2)) != 2"
 );
 
-// list take
+// list nth
 
 static_assert(
 	std::is_same<
-		tav::List<tav::Int<1>>,
-		tav::Take<
-			tav::Size<1>,
-			tav::List<tav::Int<1>, tav::Int<2>>
+		tav::Int<1>,
+		tav::Nth<
+			tav::Size<0>,
+			tav::List<tav::Int<1>>
 		>
 	>::value,
-	"(take 1 (list 1 2)) != (list 1)"
+	"(nth 0 (list 1)) != 1"
 );
 
 static_assert(
 	std::is_same<
-		tav::List<tav::Int<1>, tav::Int<2>>,
-		tav::Take<
-			tav::Size<2>,
+		tav::Int<1>,
+		tav::Nth<
+			tav::Size<0>,
 			tav::List<tav::Int<1>, tav::Int<2>>
 		>
 	>::value,
-	"(take 2 (list 1 2)) != (list 1 2)"
+	"(nth 0 (list 1 2)) != 1"
 );
 
 static_assert(
 	std::is_same<
-		tav::List<tav::Int<1>, tav::Int<2>>,
-		tav::Take<
-			tav::Size<3>,
+		tav::Int<2>,
+		tav::Nth<
+			tav::Size<1>,
 			tav::List<tav::Int<1>, tav::Int<2>>
 		>
 	>::value,
-	"(take 3 (list 1 2)) != (list 1 2)"
+	"(nth 1 (list 1 2)) != 2"
 );
 
-// list drop
-
 static_assert(
 	std::is_same<
-		tav::List<tav::Int<2>>,
-		tav::Drop<
-			tav::Size<1>,
-			tav::List<tav::Int<1>, tav::Int<2>>
-		>
+		tav::Int<1>,
+		tav::First<tav::List<tav::Int<1>, tav::Int<2>, tav::Int<3>>>
 	>::value,
-	"(drop 1 (list 1 2)) != (list 2)"
+	"(first (list 1 2 3)) != 1"
 );
 
 static_assert(
 	std::is_same<
-		void,
-		tav::Drop<
-			tav::Size<2>,
-			tav::List<tav::Int<1>, tav::Int<2>>
-		>
+		tav::Int<2>,
+		tav::Second<tav::List<tav::Int<1>, tav::Int<2>, tav::Int<3>>>
 	>::value,
-	"(drop 2 (list 1 2)) != void"
+	"(second (list 1 2 3)) != 2"
 );
 
 static_assert(
 	std::is_same<
-		void,
-		tav::Drop<
-			tav::Size<3>,
-			tav::List<tav::Int<1>, tav::Int<2>>
-		>
+		tav::Int<3>,
+		tav::Third<tav::List<tav::Int<1>, tav::Int<2>, tav::Int<3>>>
 	>::value,
-	"(drop 3 (list 1 2)) != void"
+	"(third (list 1 2 3)) != 3"
 );
 
 // list append