An implementation of pure skip lists.

Skip lists provide efficient amortized indexing deep into lists by building an index that, essentially, converts the list into a balance binary tree. See the wikipedia entry on skip lists for more information.

skip-list

Skip lists provide efficient amortized indexing deep into lists by building an index that, essentially, converts the list into a balance binary tree. See the wikipedia entry on skip lists for more information.

Performance

You can run the benchmarks using stack bench. The benchmark is the following:

let big = [0..1000] in
big == get (make big) <$> big

• For lists (get = !! and make = id)

benchmarking all/!!
time                 864.6 μs   (858.1 μs .. 873.0 μs)
                     0.999 R²   (0.999 R² .. 1.000 R²)
mean                 859.3 μs   (855.5 μs .. 864.3 μs)
std dev              14.76 μs   (11.86 μs .. 21.57 μs)

• For SkipList (get = SL.lookup and make = SL.toSkipList 32)

benchmarking Quantities/SkipList<32>
time                 134.9 μs   (134.0 μs .. 135.7 μs)
                     1.000 R²   (0.999 R² .. 1.000 R²)
mean                 134.0 μs   (133.6 μs .. 134.5 μs)
std dev              1.559 μs   (1.317 μs .. 1.958 μs)