Implemented Scheme like `Concatenate` in terms of `Fold` and `Append`

* added appropriate test case

3 files changed, 38 insertions, 3 deletions

diff --git a/src/list/list.h b/src/list/list.h
index b89e1ca..5c67872 100644
--- a/src/list/list.h
+++ b/src/list/list.h
@@ -31,5 +31,6 @@ using Tail = Cdr<Cons>;
 
 #include "operation/basic.h"
 #include "operation/append.h"
+#include "operation/concatenate.h"
 
 #endif  // TYPEASVALUE_SRC_LIST_LIST_H_
diff --git a/src/list/operation/concatenate.h b/src/list/operation/concatenate.h
new file mode 100644
index 0000000..944470b
--- /dev/null
+++ b/src/list/operation/concatenate.h
@@ -0,0 +1,18 @@
+#ifndef TYPEASVALUE_SRC_LIST_OPERATION_CONCATENATE_H_
+#define TYPEASVALUE_SRC_LIST_OPERATION_CONCATENATE_H_
+
+#include "append.h"
+#include "higher/fold.h"
+
+namespace tav {
+
+template <typename ListOfLists>
+using Concatenate = Fold<
+	Append,
+	void,
+	ListOfLists
+>;
+
+}
+
+#endif // TYPEASVALUE_SRC_LIST_OPERATION_CONCATENATE_H_
diff --git a/test.cc b/test.cc
index e8e87e1..b945899 100644
--- a/test.cc
+++ b/test.cc
@@ -317,7 +317,7 @@ static_assert(
 	"(length (take 3 (list 1 2))) != 2"
 );
 
-// list concatenate
+// list append
 
 static_assert(
 	std::is_same<
@@ -329,7 +329,7 @@ static_assert(
 			>::type
 		>::type
 	>::value,
-	"(length (concatenate (list 1) (list 2))) != 2"
+	"(length (append (list 1) (list 2))) != 2"
 );
 
 static_assert(
@@ -342,7 +342,7 @@ static_assert(
 			>::type
 		>::type
 	>::value,
-	"(length (concatenate (list 1 2) (list 3 4))) != 4"
+	"(length (append (list 1 2) (list 3 4))) != 4"
 );
 
 // list fold
@@ -491,3 +491,19 @@ static_assert(
 	>::value,
 	"(contains 0 (list 1 2 3)) != #f"
 );
+
+// list concatenate
+
+static_assert(
+	std::is_same<
+		tav::List<tav::Int<1>, tav::Int<2>, tav::Int<3>, tav::Int<4>, tav::Int<5>, tav::Int<6>>::type,
+		tav::Concatenate<
+			tav::List<
+				tav::List<tav::Int<1>, tav::Int<2>>::type,
+				tav::List<tav::Int<3>>::type,
+				tav::List<tav::Int<4>, tav::Int<5>, tav::Int<6>>::type
+			>::type
+		>::type
+	>::value,
+	"(length (concatenate (list (list 1 2) (list 3) (list 4 5 6)))) != 6"
+);