Efficent lens operation for Data.Map et al.

[Johan Tibell]

IIRC you just replace the current functions with yours and run make in
the benchmarks/ directory to compile the benchmark binaries (which use
Criterion). Then simply run them.

On Wed, Jan 18, 2012 at 8:06 AM,  <roconnor at theorem.ca> wrote:
> On Tue, 17 Jan 2012, Johan Tibell wrote:
>
>> Try it out on the Criterion benchmarks in the source repo. I'd be
>> curious to see the results.
>
>
> Okay, I never intended to try and replace the existing operations with a
> lens based one, but now you've got me curious to try.
>
> Here is my fastLens implementation:
>
> fastLens :: Key -> IntMap a -> (IntMap a -> (a -> IntMap a) -> a -> c) ->
> (IntMap a -> (a -> IntMap a) -> c) -> c
> fastLens k = k `seq` go
>  where
>    go t@(Bin p m l r) c1 c2
>      | nomatch k p m = c2 t (\x -> join k (Tip k x) p t)
>      | zero k m      = go l (updateContL c1) (updateContL c2)
>      | otherwise     = go r (updateContR c1) (updateContR c2)
>     where
>      updateContL c dl il = c (bin p m dl r) (\x -> bin p m (il x) r)
>      updateContR c dr ir = c (bin p m l dr) (\x -> bin p m r (ir x))
>    go t@(Tip ky y) c1 c2
>      | k == ky   = c1 Nil (Tip ky) y
>      | otherwise = c2 t (\x -> join k (Tip k x) ky t)
>    go Nil _ c2   = c2 Nil (Tip k)
>
> lookup :: Key -> IntMap a -> Maybe a
> lookup k t = fastLens k t (\_ _ -> Just) (\_ _ -> Nothing)
>
> insert :: Key -> a -> IntMap a -> IntMap a
> insert k x t = fastLens k t (\_ it _ -> it x) (\_ it -> it x)
>
> delete :: Key -> IntMap a -> IntMap a
> delete k t = fastLens k t (\dt _ _ -> dt) (\dt _ -> dt)
>
> update ::  (a -> Maybe a) -> Key -> IntMap a -> IntMap a
> update f k t = fastLens k t (\dt it x -> maybe dt it (f x)) (\dt _ -> dt)
>
> alter :: (Maybe a -> Maybe a) -> Key -> IntMap a -> IntMap a
> alter f k t = fastLens k t (\dt it x -> maybe dt it (f (Just x)))
>                           (\dt it   -> maybe dt it (f Nothing))
>
>
> lens :: Key -> IntMap a -> (Maybe a -> IntMap a, Maybe a)
> lens k t = fastLens k t (\dt it x -> (maybe dt it,Just x))
>                        (\dt it -> (maybe dt it,Nothing))
>
> (See also: https://github.com/roconnor/containers/tree/FastLens)
>
> How do I use criterion to benchmark this?
>
>
> --
> Russell O'Connor                                      <http://r6.ca/>
> ``All talk about `theft,''' the general counsel of the American Graphophone
> Company wrote, ``is the merest claptrap, for there exists no property in
> ideas musical, literary or artistic, except as defined by statute.''