last package:base

Extract the last element of a list, which must be finite and non-empty. WARNING: This function is partial. Consider using unsnoc instead.

Examples

>>> last [1, 2, 3]
3

>>> last [1..]
* Hangs forever *

>>> last []
*** Exception: Prelude.last: empty list

The last element of a non-empty structure.

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

Extract the last element of the stream.

Maybe monoid returning the rightmost non-Nothing value. Last a is isomorphic to Dual (First a), and thus to Dual (Alt Maybe a) Data.Semigroup.Last. The former returns the last non-Nothing, so x <> Data.Monoid.Last Nothing = x. The latter simply returns the last value, thus x <> Data.Semigroup.Last Nothing = Data.Semigroup.Last Nothing.

Examples

>>> Last (Just "hello") <> Last Nothing <> Last (Just "world")
Last {getLast = Just "world"}

>>> Last Nothing <> mempty
Last {getLast = Nothing}

Beware that Data.Semigroup.Last is different from Data.Monoid.Last. The former simply returns the last value, so x <> Data.Semigroup.Last Nothing = Data.Semigroup.Last Nothing. The latter returns the last non-Nothing, thus x <> Data.Monoid.Last Nothing = x.

Examples

>>> Last 0 <> Last 10
Last {getLast = 10}

>>> sconcat $ Last 1 :| [ Last n | n <- [2..]]
* Hangs forever *

The byte buffer just before we did our last batch of decoding.