From af5662781840ac45c21cbf14cbc7973bcf39d1da Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Tue, 17 Feb 2015 22:47:56 +0100
Subject: Reimplemented `TakeWhile` and `DropWhile` in terms of `ListIndex` *
 new higher order list operation `ListIndex` returns the index of the first
 list element satisfying a given predicate function ** this enables finding
 the split index required for both `TakeWhile` and `DropWhile` ** actual list
 manipulation is then performed using lower order `Take` or `Drop` **
 analogously to `list-index` in SRFI-1 ** added appropriate test case * added
 higher order predicate utility function `utility::predicate_assurance` ** as
 its name implies this function enables assuring that a value satisfies a
 given predicate *** if this is not the case a surrogate value is returned
 instead ** this is used to return a appropriate size value if the `ListIndex`
 call fails because no element satisfies its predicate **
 `detail::predicate_negator` was moved from `Remove`'s implementation details
 into the newly introduced `utility` namespace *** as it is required by both
 `TakeWhile` and `DropWhile` in addition to `Remove` * continuation of 8e49cc6

---
 src/list/operation/higher/list_index.h | 45 ++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 src/list/operation/higher/list_index.h

(limited to 'src/list/operation/higher/list_index.h')

diff --git a/src/list/operation/higher/list_index.h b/src/list/operation/higher/list_index.h
new file mode 100644
index 0000000..bbf43ee
--- /dev/null
+++ b/src/list/operation/higher/list_index.h
@@ -0,0 +1,45 @@
+#ifndef TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_LIST_INDEX_H_
+#define TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_LIST_INDEX_H_
+
+#include "operation/math.h"
+
+namespace tav {
+
+namespace detail {
+
+template <
+	template<typename> class Predicate,
+	typename                 List,
+	typename                 Index = Size<0>
+>
+struct index_of_first {
+	typedef If<
+		Eval<Predicate<Head<List>>>,
+		Index,
+		Eval<index_of_first<
+			Predicate,
+			Tail<List>,
+			Add<Index, Size<1>>
+		>>
+	> type;
+};
+
+template <
+	template<typename> class Predicate,
+	typename                 Index
+>
+struct index_of_first<Predicate, void, Index> {
+	typedef void type;
+};
+
+}
+
+template <
+	template<typename> class Predicate,
+	typename                 List
+>
+using ListIndex = Eval<detail::index_of_first<Predicate, List>>;
+
+}
+
+#endif  // TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_LIST_INDEX_H_
-- 
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