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{-# LANGUAGE EmptyDataDecls, RankNTypes, ScopedTypeVariables #-}
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module Example where {
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data Queue a = AQueue [a] [a];
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empty :: forall a. Queue a;
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empty = AQueue [] [];
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dequeue :: forall a. Queue a -> (Maybe a, Queue a);
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dequeue (AQueue [] []) = (Nothing, AQueue [] []);
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dequeue (AQueue xs (y : ys)) = (Just y, AQueue xs ys);
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dequeue (AQueue (v : va) []) =
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let {
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(y : ys) = reverse (v : va);
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} in (Just y, AQueue [] ys);
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enqueue :: forall a. a -> Queue a -> Queue a;
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enqueue x (AQueue xs ys) = AQueue (x : xs) ys;
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}
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