Data.List.ZigZag

The feature of this module is ZigZag and its class instances. It is an abstract data type and can be constructed / deconstructed by fromList / toList or fromDiagonals / toDiagonals. See the associated documentation for more information.

Documentation

diagonals :: [[a]] -> [[a]]

Finds the diagonals through a ragged list of lists.

For example, the diagonals of:

   [ [0,1,2]
   , []
   , [3,4]
   , [5,6,7]
   ]
 

Are:

   [ [0]
   , [1]
   , [3,2]
   , [5,4]
   , [6]
   , [7]
   ]
 

Which can be seen intuitively.

This algorithm works by storing a list of tails of rows already seen. To find the next diagonal we take the head of the next row plus the head of each stored tail. The tail remainders are stored plus the remainder of the new row.

If there are no more rows but some remaining tails we then iteratively form diagonals from the heads of each tail until there are no tails remaining.

Applied to the example:

   Row     | Output | Remaining
   --------+--------+----------------
   [0,1,2] | [0]    | [[1,2]]
   []      | [1]    | [[2]]
   [3,4]   | [3,2]  | [[4]]
   [5,6,7] | [5,4]  | [[6,7]]
   x       | [6]    | [[7]]
   x       | [7]    | []
 

fromDiagonals :: [[a]] -> ZigZag a

Convert a list of diagonals to a ZigZag.

   fromDiagonals . toDiagonals = id
   toDiagonals . fromDiagonals = id
 

fromList :: [a] -> ZigZag a

Convert a list to a ZigZag.

   fromList . toList = id
   toList . fromList = id
 

toDiagonals :: ZigZag a -> [[a]]

Convert a ZigZag to a list of diagonals.

   fromDiagonals . toDiagonals = id
   toDiagonals . fromDiagonals = id
 

toList :: ZigZag a -> [a]

Convert a ZigZag to a list.

   fromList . toList = id
   toList . fromList = id
 

data ZigZag a

A list but with a balanced enumeration of Cartesian product such that

   fmap sum (sequence (replicate n (fromList [0..])))
 

is monotonically increasing.

Example:

   sequence [fromList [0,1], fromList [0,1,2]]
   = fromDiagonals
     [ [[0,0]]
     , [[1,0],[0,1]]
     , [[1,1],[0,2]]
     , [[1,2]]
     ]
 

This variation is useful in at least two ways. One, it is not stuck on infinite factors. Two, if the factors are ordered then the product is similarly ordered; this can lend to efficient searching of product elements.

Note that this method fails for the infinitary product even if every factor is known to be non-empty. The first element is known but following it are infinite elements that each draw a second element from one of the infinite factors. A product element drawing a third factor element is never reached.

Instances

Monad ZigZag

Methods

(>>=) :: ZigZag a -> (a -> ZigZag b) -> ZigZag b

(>>) :: ZigZag a -> ZigZag b -> ZigZag b

return :: a -> ZigZag a

fail :: String -> ZigZag a

Functor ZigZag

Methods

fmap :: (a -> b) -> ZigZag a -> ZigZag b

(<$) :: a -> ZigZag b -> ZigZag a

Applicative ZigZag

Methods

pure :: a -> ZigZag a

(<*>) :: ZigZag (a -> b) -> ZigZag a -> ZigZag b

liftA2 :: (a -> b -> c) -> ZigZag a -> ZigZag b -> ZigZag c

(*>) :: ZigZag a -> ZigZag b -> ZigZag b

(<*) :: ZigZag a -> ZigZag b -> ZigZag a

Foldable ZigZag

Methods

fold :: Monoid m => ZigZag m -> m

foldMap :: Monoid m => (a -> m) -> ZigZag a -> m

foldr :: (a -> b -> b) -> b -> ZigZag a -> b

foldr' :: (a -> b -> b) -> b -> ZigZag a -> b

foldl :: (b -> a -> b) -> b -> ZigZag a -> b

foldl' :: (b -> a -> b) -> b -> ZigZag a -> b

foldr1 :: (a -> a -> a) -> ZigZag a -> a

foldl1 :: (a -> a -> a) -> ZigZag a -> a

toList :: ZigZag a -> [a]

null :: ZigZag a -> Bool

length :: ZigZag a -> Int

elem :: Eq a => a -> ZigZag a -> Bool

maximum :: Ord a => ZigZag a -> a

minimum :: Ord a => ZigZag a -> a

sum :: Num a => ZigZag a -> a

product :: Num a => ZigZag a -> a

Traversable ZigZag

Methods

traverse :: Applicative f => (a -> f b) -> ZigZag a -> f (ZigZag b)

sequenceA :: Applicative f => ZigZag (f a) -> f (ZigZag a)

mapM :: Monad m => (a -> m b) -> ZigZag a -> m (ZigZag b)

sequence :: Monad m => ZigZag (m a) -> m (ZigZag a)

Eq1 ZigZag

Methods

liftEq :: (a -> b -> Bool) -> ZigZag a -> ZigZag b -> Bool

Ord1 ZigZag

Methods

liftCompare :: (a -> b -> Ordering) -> ZigZag a -> ZigZag b -> Ordering

Read1 ZigZag

Methods

liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (ZigZag a)

liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [ZigZag a]

liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (ZigZag a)

liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [ZigZag a]

Show1 ZigZag

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> ZigZag a -> ShowS

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [ZigZag a] -> ShowS

Alternative ZigZag

Methods

empty :: ZigZag a

(<|>) :: ZigZag a -> ZigZag a -> ZigZag a

some :: ZigZag a -> ZigZag [a]

many :: ZigZag a -> ZigZag [a]

MonadPlus ZigZag

Methods

mzero :: ZigZag a

mplus :: ZigZag a -> ZigZag a -> ZigZag a

IsList (ZigZag a)

Associated Types

type Item (ZigZag a) :: *

Methods

fromList :: [Item (ZigZag a)] -> ZigZag a

fromListN :: Int -> [Item (ZigZag a)] -> ZigZag a

toList :: ZigZag a -> [Item (ZigZag a)]

Eq a => Eq (ZigZag a)

Methods

(==) :: ZigZag a -> ZigZag a -> Bool

(/=) :: ZigZag a -> ZigZag a -> Bool

Data a => Data (ZigZag a)

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> ZigZag a -> c (ZigZag a)

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (ZigZag a)

toConstr :: ZigZag a -> Constr

dataTypeOf :: ZigZag a -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c (ZigZag a))

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (ZigZag a))

gmapT :: (forall b. Data b => b -> b) -> ZigZag a -> ZigZag a

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> ZigZag a -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> ZigZag a -> r

gmapQ :: (forall d. Data d => d -> u) -> ZigZag a -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> ZigZag a -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> ZigZag a -> m (ZigZag a)

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> ZigZag a -> m (ZigZag a)

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> ZigZag a -> m (ZigZag a)

Ord a => Ord (ZigZag a)

Methods

compare :: ZigZag a -> ZigZag a -> Ordering

(<) :: ZigZag a -> ZigZag a -> Bool

(<=) :: ZigZag a -> ZigZag a -> Bool

(>) :: ZigZag a -> ZigZag a -> Bool

(>=) :: ZigZag a -> ZigZag a -> Bool

max :: ZigZag a -> ZigZag a -> ZigZag a

min :: ZigZag a -> ZigZag a -> ZigZag a

Read a => Read (ZigZag a)

Methods

readsPrec :: Int -> ReadS (ZigZag a)

readList :: ReadS [ZigZag a]

readPrec :: ReadPrec (ZigZag a)

readListPrec :: ReadPrec [ZigZag a]

Show a => Show (ZigZag a)

Methods

showsPrec :: Int -> ZigZag a -> ShowS

show :: ZigZag a -> String

showList :: [ZigZag a] -> ShowS

Generic (ZigZag a)

Associated Types

type Rep (ZigZag a) :: * -> *

Methods

from :: ZigZag a -> Rep (ZigZag a) x

to :: Rep (ZigZag a) x -> ZigZag a

Semigroup (ZigZag a)

Methods

(<>) :: ZigZag a -> ZigZag a -> ZigZag a

sconcat :: NonEmpty (ZigZag a) -> ZigZag a

stimes :: Integral b => b -> ZigZag a -> ZigZag a

Monoid (ZigZag a)

Methods

mempty :: ZigZag a

mappend :: ZigZag a -> ZigZag a -> ZigZag a

mconcat :: [ZigZag a] -> ZigZag a

Generic1 * ZigZag

Associated Types

type Rep1 ZigZag (f :: ZigZag -> *) :: k -> *

Methods

from1 :: f a -> Rep1 ZigZag f a

to1 :: Rep1 ZigZag f a -> f a

type Rep (ZigZag a)

type Rep (ZigZag a)

type Item (ZigZag a)

type Item (ZigZag a) = a

type Rep1 * ZigZag

type Rep1 * ZigZag