A bug of dropWhileR in Data.Sequence

[kazu-yamamoto]

The document of dropWhileR says: dropWhileR p xs is equivalent to reverse (dropWhileL p (reverse xs)).

However,

reverse $ dropWhileL (==4) $ reverse $ fromList [1,2,3,4]
==> fromList [1,2,3]

dropWhileR (==4) $ fromList [1,2,3,4]
==> fromList [1,2]

I guess the cause of bug is in breakl.

Original:

breakl p xs = foldr (\ i _ -> S.splitAt i xs) (xs, empty) (findIndicesL p xs)

Fixed:

breakl p xs = foldr (\ i _ -> S.splitAt (i+1) xs) (xs, empty) (findIndicesL p xs)

[igloo]

Thanks for the report; fixed:

Sun Jul  4 07:06:27 PDT 2010  Ian Lynagh <igloo@earth.li>
  * Fix Data.Sequence's breakr, and add a test for it; fixes trac #4157