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

[David Feuer]

It can be, but your way traverses the entire haystack *twice*. The memory
needs are equivalent to the reversing version, which I consider
unacceptable.

On Sat, Oct 11, 2014 at 5:57 AM, Andreas Abel <abela at chalmers.se> wrote:

> David, the essence of your idea seems mutually drop the correct number of
> elements from needle and hay and then compare for equality.  Here is a
> concise implementation of your idea in terms of drop:
>
> isSuffixOf        :: forall a . (Eq a) => [a] -> [a] -> Bool
> [] `isSuffixOf` _  =  True
> xs `isSuffixOf` ys =  xs == drop (length (drop (length xs) ys)) ys
>
> This can be further simplified to
>
> isSuffixOf        :: forall a . (Eq a) => [a] -> [a] -> Bool
> [] `isSuffixOf` _  =  True
> xs `isSuffixOf` ys =  xs == drop (length ys - length xs) ys
>
> which is a very easy to understand program, I think, without need to
> reverse lists.
>
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