POLYINT: first try of polygon intersection algorithm in O(n)

QueueEx.hs

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+module QueueEx where
+
+import           Control.Applicative
+import           Data.Dequeue (BankersDequeue)
+import qualified Data.Dequeue           as Q
+import           Data.Maybe
+
+
+-- |Shift a queue to the left, such as:
+-- [1, 2, 3] -> [2, 3, 1]
+shiftQueueLeft :: BankersDequeue a -> BankersDequeue a
+shiftQueueLeft  = (\(b, nq) -> Q.pushBack nq (fromJust b)) <$> Q.popFront
+
+
+-- |Shift a queue to the right, such as:
+-- [1, 2, 3] -> [3, 1, 2]
+shiftQueueRight :: BankersDequeue a -> BankersDequeue a
+shiftQueueRight = (\(b, nq) -> Q.pushFront nq (fromJust b)) <$> Q.popBack
+
+
+-- |Convert a Queue back to a list.
+queueToList :: BankersDequeue a -> [a]
+queueToList q = Q.takeFront (Q.length q) q
+
+
+-- |Unsafe version of Q.first.
+uQfirst :: BankersDequeue a -> a
+uQfirst = fromJust . Q.first