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

1 files changed, 2 insertions, 11 deletions

diff --git a/src/list/operation/higher/remove.h b/src/list/operation/higher/remove.h
index 598f5a6..6770359 100644
--- a/src/list/operation/higher/remove.h
+++ b/src/list/operation/higher/remove.h
@@ -2,25 +2,16 @@
 #define TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_REMOVE_H_
 
 #include "filter.h"
+#include "utility/predicate.h"
 
 namespace tav {
 
-namespace detail {
-
-template <template<typename> class Predicate>
-struct predicate_negator {
-	template <typename Element>
-	using function = Not<Predicate<Element>>;
-};
-
-}
-
 template <
 	template<typename> class Predicate,
 	typename                 List
 >
 using Remove = Filter<
-	detail::predicate_negator<Predicate>::template function,
+	utility::predicate_negator<Predicate>::template function,
 	List
 >;