RIO.List.Partial

Basic functions

head :: [a] -> a

Extract the first element of a list, which must be non-empty.

last :: [a] -> a

Extract the last element of a list, which must be finite and non-empty.

tail :: [a] -> [a]

Extract the elements after the head of a list, which must be non-empty.

init :: [a] -> [a]

Return all the elements of a list except the last one. The list must be non-empty.

Reducing lists (folds)

foldl1 :: Foldable t => (a -> a -> a) -> t a -> a

A variant of foldl that has no base case, and thus may only be applied to non-empty structures.

foldl1 f = foldl1 f . toList

foldl1' :: (a -> a -> a) -> [a] -> a

A strict version of foldl1

foldr1 :: Foldable t => (a -> a -> a) -> t a -> a

A variant of foldr that has no base case, and thus may only be applied to non-empty structures.

foldr1 f = foldr1 f . toList

Special folds

maximum :: (Foldable t, Ord a) => t a -> a

The largest element of a non-empty structure.

minimum :: (Foldable t, Ord a) => t a -> a

The least element of a non-empty structure.

maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a

The largest element of a non-empty structure with respect to the given comparison function.

minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a

The least element of a non-empty structure with respect to the given comparison function.

Building lists

Scans

scanl1 :: (a -> a -> a) -> [a] -> [a]

scanl1 is a variant of scanl that has no starting value argument:

scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]

scanr1 :: (a -> a -> a) -> [a] -> [a]

scanr1 is a variant of scanr that has no starting value argument.

Indexing lists

(!!) :: [a] -> Int -> a infixl 9

List index (subscript) operator, starting from 0. It is an instance of the more general genericIndex, which takes an index of any integral type.