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Add Semigroup Superclass #1

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Add Semigroup Superclass #1

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8 changes: 5 additions & 3 deletions Control/Monad/Levels.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,9 +45,10 @@ newtype Levels a = Levels { levels :: [FMList a] }
runLevels :: Levels a -> [a]
runLevels = toList . foldr append empty . levels

instance Semigroup (Levels a) where
a <> b = Levels (empty : merge (levels a) (levels b))
instance Monoid (Levels a) where
mempty = Levels []
a `mappend` b = Levels (empty : merge (levels a) (levels b))

-- like 'zipWith append' without cutting the longer list
merge :: [FMList a] -> [FMList a] -> [FMList a]
Expand Down Expand Up @@ -80,7 +81,8 @@ idfsBy n a = toList $ foldr append empty [ unFM a yield ! d | d <- [0,n..] ]
-- to iterative deepening search.
newtype DepthBound a = DepthBound { (!) :: Int -> FMList a }

instance Semigroup (DepthBound a) where
a <> b = DepthBound (\d -> if d==0 then empty
else append (a!(d-1)) (b!(d-1)))
instance Monoid (DepthBound a) where
mempty = DepthBound (const empty)
a `mappend` b = DepthBound (\d -> if d==0 then empty
else append (a!(d-1)) (b!(d-1)))