Redefined `Length` in terms of `Apply` and `Fold`

* this function illustrates the use case `Apply` is currently intended for
* moved `Take` and `Nth` into separate files to resolve header resolution conflicts

6 files changed, 83 insertions, 68 deletions

diff --git a/src/function/apply.h b/src/function/apply.h
index 6012a01..8e780e0 100644
--- a/src/function/apply.h
+++ b/src/function/apply.h
@@ -3,6 +3,9 @@
 
 #include <type_traits>
 
+#include "list/list.h"
+#include "list/operation/nth.h"
+
 namespace tav {
 
 namespace detail {
@@ -45,8 +48,6 @@ template <
 	typename...                 Arguments
 >
 struct Apply {
-	typedef typename tav::List<Arguments...>::type argument_list;
-
 	template <typename... Partials>
 	using variadic_type = Function<
 		typename detail::resolve_placeholder<
diff --git a/src/list/list.h b/src/list/list.h
index 5c67872..c03a0ef 100644
--- a/src/list/list.h
+++ b/src/list/list.h
@@ -30,6 +30,8 @@ using Tail = Cdr<Cons>;
 }
 
 #include "operation/basic.h"
+#include "operation/nth.h"
+#include "operation/take.h"
 #include "operation/append.h"
 #include "operation/concatenate.h"
 
diff --git a/src/list/operation/basic.h b/src/list/operation/basic.h
index d80b347..1f4b043 100644
--- a/src/list/operation/basic.h
+++ b/src/list/operation/basic.h
@@ -1,76 +1,18 @@
 #ifndef TYPEASVALUE_SRC_LIST_OPERATION_BASIC_H_
 #define TYPEASVALUE_SRC_LIST_OPERATION_BASIC_H_
 
-#include "operation/math.h"
 #include "higher/fold.h"
+#include "function/apply.h"
+#include "operation/math.h"
 
 namespace tav {
 
 template <typename Cons>
-class Length {
-	private:
-		template <
-			typename,
-			typename Previous
-		>
-		struct count {
-			typedef Add<Size<1>, Previous> type;
-		};
-
-	public:
-		typedef typename Fold<count, Size<0>, Cons>::type type;
-
-};
-
-template <
-	typename Index,
-	typename Cons
->
-struct Nth {
-	typedef typename Nth<
-		Substract<Index, Size<1>>,
-		Tail<Cons>
-	>::type type;
-};
-
-template <typename Index>
-struct Nth<Index, void> {
-	typedef void type;
-};
-
-template <typename Cons>
-struct Nth<Size<0>, Cons> {
-	typedef Head<Cons> 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;
-};
+using Length = Fold<
+	Apply<Add, Size<1>, _1>::pair_type,
+	Size<0>,
+	Cons
+>;
 
 }
 
diff --git a/src/list/operation/nth.h b/src/list/operation/nth.h
new file mode 100644
index 0000000..8eb88ba
--- /dev/null
+++ b/src/list/operation/nth.h
@@ -0,0 +1,31 @@
+#ifndef TYPEASVALUE_SRC_LIST_OPERATION_NTH_H_
+#define TYPEASVALUE_SRC_LIST_OPERATION_NTH_H_
+
+#include "operation/math.h"
+
+namespace tav {
+
+template <
+	typename Index,
+	typename Cons
+>
+struct Nth {
+	typedef typename Nth<
+		Substract<Index, Size<1>>,
+		Tail<Cons>
+	>::type type;
+};
+
+template <typename Cons>
+struct Nth<Size<0>, Cons> {
+	typedef Head<Cons> type;
+};
+
+template <typename Index>
+struct Nth<Index, void> {
+	typedef void type;
+};
+
+}
+
+#endif  // TYPEASVALUE_SRC_LIST_OPERATION_NTH_H_
diff --git a/src/list/operation/take.h b/src/list/operation/take.h
new file mode 100644
index 0000000..db25640
--- /dev/null
+++ b/src/list/operation/take.h
@@ -0,0 +1,40 @@
+#ifndef TYPEASVALUE_SRC_LIST_OPERATION_TAKE_H_
+#define TYPEASVALUE_SRC_LIST_OPERATION_TAKE_H_
+
+#include "operation/math.h"
+
+namespace tav {
+
+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_TAKE_H_
diff --git a/test.cc b/test.cc
index 0c16126..33d0248 100644
--- a/test.cc
+++ b/test.cc
@@ -7,7 +7,6 @@
 #include "list/list.h"
 #include "list/operation/reverse.h"
 #include "list/operation/contains.h"
-#include "list/operation/higher/fold.h"
 #include "list/operation/higher/misc.h"
 #include "list/operation/higher/query.h"
 #include "list/generator/iota.h"