In my boredom, I implemented the toy sorting algorithm called Gnome Sort. It accomplishes backtracking by using a zipper-like system of two lists treated as stacks, and is about 100X slower than GHC’s merge sort on the test I used. It’s also not especially small or simple-looking. It’s basically terrible:

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gnomeSort :: (Ord a)=> [a] -> [a]
gnomeSort = sort []
    where sort rs [] = rs
          sort [] (x:xs) = sort [x] xs
          sort (r:rs) (x:xs)
              | x > r = sort rs (x:r:xs)
              | otherwise = sort (x:r:rs) xs

The above doesn’t keep track of where it left off before it began to backtrack, an obvious optimization which turned the algorithm into an insertion sort:

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import Data.List (insert)

insertSort :: (Ord a)=> [a] -> [a]
insertSort = sort []
    where sort rs [] = rs
          sort rs (x:xs) = sort (insert x rs) xs

about 60X slower than Data.List.sort.