[Haskell-cafe] getting last char of String

[Maciej Piechotka]

On Sat, 2011-01-01 at 19:27 +1100, Jesse Schalken wrote:
> 
> On Sat, Jan 1, 2011 at 8:54 AM, Felipe Almeida Lessa
> <felipe.lessa at gmail.com> wrote:
>         On Fri, Dec 31, 2010 at 6:43 PM, aditya siram
>         <aditya.siram at gmail.com> wrote:
>         > -- untested and won't work on an infinite list
>         > last :: [a] -> a
>         > last = head . reverse
>         
>         
>         No definition for last works with infinite lists =). 
> 
> 
> Unless you make the result nullable, of course.
> 
> 
> maybeLast :: [a] -> Maybe a
> 
> maybeLast [] = Nothing
> maybeLast [x] = Just x
> maybeLast (_:xs) = maybeLast xs
> 

It may or may not be expected but it may also be written as:

maybeLast' [] = Nothing
maybeLast' (x:xs) = Just (fromMaybe x (maybeLast xs))

The main differences are:

maybeLast  (x:_|_) = _|_
maybeLast' (x:_|_) = Just _|_

maybeLast  (fix (x:)) = _|_
maybeLast' (fix (x:)) = Just _|_

Regards

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