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add an Ord instance #3

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add an Ord instance #3

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4 changes: 4 additions & 0 deletions Data/List/PointedList.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,10 @@ prefix f (PointedList ls x rs) = (\ls' -> PointedList (reverse ls') x rs) <$> f
instance (Show a) => Show (PointedList a) where
show (PointedList ls x rs) = show (reverse ls) ++ " " ++ show x ++ " " ++ show rs

-- | `fromList l <= fromList m` if and only if `l <= m`
instance Ord a => Ord (PointedList a) where
compare pl ql = compare (toList pl) (toList ql)

instance Functor PointedList where
fmap f (PointedList ls x rs) = PointedList (map f ls) (f x) (map f rs)

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