From e317b6c9318766eabda53d9dc6e9cdac55aae34b Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Sun, 1 Feb 2015 12:57:22 +0100
Subject: Added `TakeWhile` higher order list operation * as its name implies
 this function returns the longest initial prefix of a list that satisfies a
 given _Predicate_ * added appropriate test case

---
 src/list/operation/higher/take_while.h | 33 +++++++++++++++++++++++++++++
 test.cc                                | 38 +++++++++++++++++++++++++++++++++-
 2 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 src/list/operation/higher/take_while.h

diff --git a/src/list/operation/higher/take_while.h b/src/list/operation/higher/take_while.h
new file mode 100644
index 0000000..01062f4
--- /dev/null
+++ b/src/list/operation/higher/take_while.h
@@ -0,0 +1,33 @@
+#ifndef TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_TAKE_WHILE_H_
+#define TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_TAKE_WHILE_H_
+
+#include "type.h"
+#include "conditional/if.h"
+
+namespace tav {
+
+template <
+	template<typename> class Predicate,
+	typename                 Current
+>
+struct TakeWhile {
+	typedef If<
+		Predicate<Head<Current>>::type::value,
+		Cons<
+			Head<Current>,
+			typename TakeWhile<Predicate, Tail<Current>>::type
+		>,
+		void
+	> type;
+};
+
+template <
+	template<typename> class Predicate
+>
+struct TakeWhile<Predicate, void> {
+	typedef void type;
+};
+
+}
+
+#endif  // TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_TAKE_WHILE_H_
diff --git a/test.cc b/test.cc
index 014a974..6accc0e 100644
--- a/test.cc
+++ b/test.cc
@@ -12,6 +12,7 @@
 #include "list/operation/higher/partition.h"
 #include "list/operation/higher/query.h"
 #include "list/operation/higher/find.h"
+#include "list/operation/higher/take_while.h"
 #include "list/generator/iota.h"
 #include "list/generator/make_list.h"
 #include "list/generator/higher/list_tabulate.h"
@@ -683,7 +684,7 @@ static_assert(
 	"(count even? (list 1 3 5)) != 0"
 );
 
-//list find
+// list find
 
 static_assert(
 	std::is_same<
@@ -718,6 +719,41 @@ static_assert(
 	"(find even? (list 1 3 5)) != #f"
 );
 
+// list take while
+
+static_assert(
+	std::is_same<
+		tav::List<tav::Int<2>, tav::Int<4>>::type,
+		tav::TakeWhile<
+			tav::Even,
+			tav::List<tav::Int<2>, tav::Int<4>, tav::Int<5>, tav::Int<6>>::type
+		>::type
+	>::value,
+	"(take-while even? (list 2 4 5 6)) != (list 2 4)"
+);
+
+static_assert(
+	std::is_same<
+		tav::List<tav::Int<2>, tav::Int<4>, tav::Int<6>>::type,
+		tav::TakeWhile<
+			tav::Even,
+			tav::List<tav::Int<2>, tav::Int<4>, tav::Int<6>>::type
+		>::type
+	>::value,
+	"(take-while even? (list 2 4 6)) != (list 2 4 6)"
+);
+
+static_assert(
+	std::is_same<
+		void,
+		tav::TakeWhile<
+			tav::Odd,
+			tav::List<tav::Int<2>, tav::Int<4>, tav::Int<5>, tav::Int<6>>::type
+		>::type
+	>::value,
+	"(take-while odd? (list 2 4 5 6)) != void"
+);
+
 // function apply
 
 static_assert(
-- 
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