Ways to pack (adjacent) elements of a list into 2-tuples

Question

I was wondering if there would be a concise/one-liner way to do the following:

pack :: [a] -> [(a, a)]
pack []       = []
pack [_]      = []
pack (x:y:xs) = (         


        

Answer 1

We can easily split the list into two lists with alternating elements with this tidbit (due to HaskellWiki)

 foldr (\a ~(x,y) -> (a:y,x)) ([],[])

All that remains is to combine the lists with zip

pack :: [a] -> [(a, a)]
pack = uncurry zip . foldr (\a ~(x,y) -> (a:y,x)) ([],[])