1  module Utils.Sequence (firstValue, lastValue, withoutLast) where
 2  
 3  import Data.Sequence as Seq (ViewL (EmptyL, (:<)), length, lookup, null, take, viewl)
 4  import Text.Pandoc.Builder (Many (Many, unMany))
 5  
 6  -- Gets the first value of a sequence wrapped in Many
 7  firstValue :: Many a -> Maybe a
 8  firstValue many = case Seq.viewl xs of
 9    Seq.EmptyL -> Nothing
10    x Seq.:< _ -> Just x
11    where
12      xs = unMany many
13  
14  -- Gets the last value of a sequence wrapped in Many
15  lastValue :: Many a -> Maybe a
16  lastValue many = Seq.lookup (Seq.length extractedSeq - 1) extractedSeq
17    where
18      extractedSeq = unMany many
19  
20  -- Return a sequence without the last element of the input sequence
21  withoutLast :: Many a -> Many a
22  withoutLast many
23    | Seq.null xs = many
24    | otherwise = Many $ Seq.take (Seq.length xs - 1) xs
25    where
26      xs = unMany many