Proposal: Make a very slight change to the semantics of Data.List.isSuffixOf

[Milan Straka]

Hi all,

> -----Original message-----
> From: David Feuer <david.feuer at gmail.com>
> Sent: 10 Oct 2014, 05:23
>
> On Fri, Oct 10, 2014 at 5:18 AM, Jon Fairbairn <jon.fairbairn at cl.cam.ac.uk>
> wrote:
> 
> > That seems rather wordy to me. Can we get anywhere starting with
> >
> >
> It is rather wordy; I just don't know how to do better.

What about something like the following? It uses exactly the same
algorithm, it just avoids the maybe combinator and Maybe internal
result, and renames stuff:

isSuffixOf :: (Eq a) => [a] -> [a] -> Bool 
[] `isSuffixOf` _ = True
needle `isSuffixOf` hay = subtract_and_compare needle hay
  where subtract_and_compare [] diff = skip_and_compare diff hay
        subtract_and_compare _ [] = False -- needle longer than hay
        subtract_and_compare (n:ns) (h:hs) = subtract_and_compare ns hs

        skip_and_compare [] suffix = needle == suffix
        skip_and_compare _ [] = True -- first argument must also be []
        skip_and_compare (d:ds) (s:ss) = skip_and_compare ds ss

The redundant skip_and_compare case is there just for completeness and
readability.

Cheers,
Milan