Implement Applicative based API #522
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generateA is used as primitive and all other functions are expressed in it terms. First version goes through intermediate list. This is simplest implementation possible and would serve as baseline for further optimizations
We establish implementation which goes through list as baseline and the we can try to optimize it. Note definition of foldlOf'. It's different from definition in lens<=5.3.3 but it's absolutely necessary to get good perfomance in folds
Does wonders for traversals using Identity
konsumlamm
reviewed
Jan 28, 2025
| go !i | i >= n = pure $ STA unsafeFreeze | ||
| | otherwise = (\a (STA m) -> STA $ \mv -> M.unsafeWrite mv i a >> m mv) | ||
| <$> f i | ||
| <*> go (i + 1) |
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It's probably better to use liftA2 here.
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Probably. But I'm not sure that STA will survive maybe some New-like variant will perform better
Co-authored-by: konsumlamm <[email protected]>
Good point! I forgot about them. But they're simpler since in this case one isn't in business of constructing vector so it simply reduces to fold. |
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Implementation follows plan described in #477 with
generateA :: Applicative f => Int -> (Int -> f a) -> f (v a)as primitive. It is not subject to stream fusion.Writing
generateAis not difficult. Problem is doing it efficiently. Current benchmarks are (suggestions for more are very welcome):First and naive implementation uses list as intermediate data structure. Sum benchmark performs well in this case. Using
STAinstead brings map benchmark on par with explicit loop and produces slight (5-10%) improvements in state and IO benchmark)Currently sum and map perform on par with explicit loop. State gives 7x slowdown and 8x allocations, IO benchmark 4x slowdown and 8x allocations. We obviously can add rewrite rules for
IO/STbut maybe there're more general optimizations.Fixes #477, #69, #132, #144