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/drop_while.h | 42 +++++++++++++---------------------
 1 file changed, 16 insertions(+), 26 deletions(-)

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

diff --git a/src/list/operation/higher/drop_while.h b/src/list/operation/higher/drop_while.h
index 021698f..1207020 100644
--- a/src/list/operation/higher/drop_while.h
+++ b/src/list/operation/higher/drop_while.h
@@ -1,38 +1,28 @@
 #ifndef TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_DROP_WHILE_H_
 #define TYPEASVALUE_SRC_LIST_OPERATION_HIGHER_DROP_WHILE_H_
 
-#include "conditional/if.h"
+#include "list_index.h"
+#include "list/operation/drop.h"
+#include "utility/predicate.h"
 
 namespace tav {
 
-namespace detail {
-
-template <
-	template<typename> class Predicate,
-	typename                 Current
->
-struct DropWhile {
-	typedef If<
-		Eval<Predicate<Head<Current>>>,
-		Eval<DropWhile<Predicate, Tail<Current>>>,
-		Current
-	> type;
-};
-
-template <
-	template<typename> class Predicate
->
-struct DropWhile<Predicate, void> {
-	typedef void type;
-};
-
-}
-
 template <
 	template<typename> class Predicate,
-	typename                 Current
+	typename                 List
 >
-using DropWhile = Eval<detail::DropWhile<Predicate, Current>>;
+using DropWhile = Drop<
+	typename utility::predicate_assurance<
+		utility::predicate_negator<std::is_void>::template function,
+		Length<List>
+	>::template assure<
+		ListIndex<
+			utility::predicate_negator<Predicate>::template function,
+			List
+		>
+	>,
+	List
+>;
 
 }
 
-- 
cgit v1.2.3