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/utility/predicate.h | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 src/utility/predicate.h

(limited to 'src/utility')

diff --git a/src/utility/predicate.h b/src/utility/predicate.h
new file mode 100644
index 0000000..f06fcee
--- /dev/null
+++ b/src/utility/predicate.h
@@ -0,0 +1,34 @@
+#ifndef TYPEASVALUE_SRC_UTILITY_PREDICATE_H_
+#define TYPEASVALUE_SRC_UTILITY_PREDICATE_H_
+
+#include "conditional/if.h"
+#include "operation/logic.h"
+
+namespace tav {
+
+namespace utility {
+
+template <
+	template<typename> class Predicate,
+	typename                 Surrogate
+>
+struct predicate_assurance {
+	template <typename Value>
+	using assure = If<
+		Eval<Predicate<Value>>,
+		Value,
+		Surrogate
+	>;
+};
+
+template <template<typename> class Predicate>
+struct predicate_negator {
+	template <typename Element>
+	using function = Not<Predicate<Element>>;
+};
+
+}
+
+}
+
+#endif  // TYPEASVALUE_SRC_UTILITY_PREDICATE_H_
-- 
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