From a3cfc224111c324324e29a9a7a61b511053ec14c Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Wed, 18 Feb 2015 20:23:35 +0100
Subject: Reimplemented `Append` in terms of `Fold` * `Fold` already implements
 the necessary partial specializations for traversing list structures

---
 src/list/operation/append.h      | 40 ++++++++++++++++++++++------------------
 src/list/operation/concatenate.h |  1 +
 src/list/operation/reverse.h     |  2 +-
 3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/src/list/operation/append.h b/src/list/operation/append.h
index 2dcd184..77f72d9 100644
--- a/src/list/operation/append.h
+++ b/src/list/operation/append.h
@@ -1,27 +1,23 @@
 #ifndef TYPEASVALUE_SRC_LIST_OPERATION_APPEND_H_
 #define TYPEASVALUE_SRC_LIST_OPERATION_APPEND_H_
 
+#include "higher/fold.h"
+
 namespace tav {
 
 namespace detail {
 
-template <
-	typename Primary,
-	typename Secondary
->
-struct Append {
-	typedef Cons<
-		Head<Primary>,
-		Eval<Append<
-			Tail<Primary>,
-			Secondary
-		>>
-	> type;
-};
-
-template <typename Secondary>
-struct Append<void, Secondary> {
-	typedef Secondary type;
+template <typename Replacement>
+struct replace_void_cdr {
+	template <typename CAR, typename CDR>
+	using function = Cons<
+		CAR,
+		If<
+			Eval<std::is_void<CDR>>,
+			Replacement,
+			CDR
+		>
+	>;
 };
 
 }
@@ -30,7 +26,15 @@ template <
 	typename Primary,
 	typename Secondary
 >
-using Append = Eval<detail::Append<Primary, Secondary>>;
+using Append = If<
+	Eval<std::is_void<Primary>>,
+	Secondary,
+	Fold<
+		detail::replace_void_cdr<Secondary>::template function,
+		void,
+		Primary
+	>
+>;
 
 }
 
diff --git a/src/list/operation/concatenate.h b/src/list/operation/concatenate.h
index 944470b..a5cbaa6 100644
--- a/src/list/operation/concatenate.h
+++ b/src/list/operation/concatenate.h
@@ -2,6 +2,7 @@
 #define TYPEASVALUE_SRC_LIST_OPERATION_CONCATENATE_H_
 
 #include "append.h"
+#include "higher/remove.h"
 #include "higher/fold.h"
 
 namespace tav {
diff --git a/src/list/operation/reverse.h b/src/list/operation/reverse.h
index 6d9237d..cabc229 100644
--- a/src/list/operation/reverse.h
+++ b/src/list/operation/reverse.h
@@ -12,7 +12,7 @@ template <
 	typename Current,
 	typename Previous
 >
-using reversed_append = tav::Append<Previous, List<Current>>;
+using reversed_append = Append<Previous, List<Current>>;
 
 }
 
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