From 9bb66d9c1d8a7bf5bf02f5a7c400894e928d2a95 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Wed, 18 Feb 2015 22:37:39 +0100
Subject: Changed `ListIndex` to return false if no index is found *
 analogously to `list-index` and `find` in SRFI-1

---
 src/list/operation/higher/drop_while.h | 2 +-
 src/list/operation/higher/list_index.h | 2 +-
 src/list/operation/higher/take_while.h | 2 +-
 src/type.h                             | 6 ++++++
 test.cc                                | 4 ++--
 5 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/list/operation/higher/drop_while.h b/src/list/operation/higher/drop_while.h
index 1207020..8d013f9 100644
--- a/src/list/operation/higher/drop_while.h
+++ b/src/list/operation/higher/drop_while.h
@@ -13,7 +13,7 @@ template <
 >
 using DropWhile = Drop<
 	typename utility::predicate_assurance<
-		utility::predicate_negator<std::is_void>::template function,
+		IsSize,
 		Length<List>
 	>::template assure<
 		ListIndex<
diff --git a/src/list/operation/higher/list_index.h b/src/list/operation/higher/list_index.h
index bbf43ee..d665b82 100644
--- a/src/list/operation/higher/list_index.h
+++ b/src/list/operation/higher/list_index.h
@@ -29,7 +29,7 @@ template <
 	typename                 Index
 >
 struct index_of_first<Predicate, void, Index> {
-	typedef void type;
+	typedef Boolean<false> type;
 };
 
 }
diff --git a/src/list/operation/higher/take_while.h b/src/list/operation/higher/take_while.h
index f9fc3aa..105e83c 100644
--- a/src/list/operation/higher/take_while.h
+++ b/src/list/operation/higher/take_while.h
@@ -13,7 +13,7 @@ template <
 >
 using TakeWhile = Take<
 	typename utility::predicate_assurance<
-		utility::predicate_negator<std::is_void>::template function,
+		IsSize,
 		Length<List>
 	>::template assure<
 		ListIndex<
diff --git a/src/type.h b/src/type.h
index 508e22f..c2ad2d8 100644
--- a/src/type.h
+++ b/src/type.h
@@ -38,6 +38,12 @@ using IsEqualValue = Boolean<X::value == Y::value>;
 template <typename X>
 using IsTrue = IsEqualValue<X, Boolean<true>>;
 
+template <typename X>
+using IsBoolean = Eval<std::is_same<typename X::value_type, bool>>;
+
+template <typename X>
+using IsSize = Eval<std::is_same<typename X::value_type, std::size_t>>;
+
 }
 
 #endif  // TYPEASVALUE_SRC_TYPE_H_
diff --git a/test.cc b/test.cc
index 6a957b1..5742fb2 100644
--- a/test.cc
+++ b/test.cc
@@ -922,13 +922,13 @@ static_assert(
 
 static_assert(
 	std::is_same<
-		void,
+		tav::Boolean<false>,
 		tav::ListIndex<
 			tav::Even,
 			tav::List<tav::Int<1>, tav::Int<3>, tav::Int<5>>
 		>
 	>::value,
-	"(list-index even? (list 1 3 5)) != void"
+	"(list-index even? (list 1 3 5)) != #f"
 );
 
 // list find
-- 
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