Universum.List.Safe

This module contains safe functions to work with list type (mostly with NonEmpty).

Documentation

uncons :: [a] -> Maybe (a, [a])

Destructuring list into its head and tail if possible. This function is total.

>>> uncons []
Nothing
>>> uncons [1..5]
Just (1,[2,3,4,5])
>>> uncons (5 : [1..5]) >>= \(f, l) -> pure $ f == length l
Just True

whenNotNull :: Applicative f => [a] -> (NonEmpty a -> f ()) -> f ()

Performs given action over NonEmpty list if given list is non empty.

>>> whenNotNull [] $ \(b :| _) -> print (not b)
>>> whenNotNull [False,True] $ \(b :| _) -> print (not b)
True

whenNotNullM :: Monad m => m [a] -> (NonEmpty a -> m ()) -> m ()

Monadic version of whenNotNull.

foldr1 :: (a -> a -> a) -> NonEmpty a -> a

A variant of foldr that has no base case, and thus may only be applied to NonEmpty.

>>> foldr1 (+) (1 :| [2,3,4,5])
15

foldl1 :: (a -> a -> a) -> NonEmpty a -> a

A variant of foldl that has no base case, and thus may only be applied to NonEmpty.

>>> foldl1 (+) (1 :| [2,3,4,5])
15

minimum :: Ord a => NonEmpty a -> a

The least element of a NonEmpty.

>>> minimum (1 :| [2,3,4,5])
1

maximum :: Ord a => NonEmpty a -> a

The largest element of a NonEmpty.

>>> maximum (1 :| [2,3,4,5])
5

minimumBy :: (a -> a -> Ordering) -> NonEmpty a -> a

The least element of a NonEmpty with respect to the given comparison function.

maximumBy :: (a -> a -> Ordering) -> NonEmpty a -> a

The largest element of a NonEmpty with respect to the given comparison function.