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foldMap, foldMap' for PrimArray #186

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foldMap, foldMap' for PrimArray #186

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ff7f68a
foldMap, foldMap'
chessai Jul 15, 2018
6948536
update changelog
chessai Jul 16, 2018
853b996
Merge branch 'master' of github.com:haskell/primitive into foldable-p…
chessai Sep 17, 2018
af41b39
fix ordering of mappend in foldMapPrimArray
chessai Sep 17, 2018
0bb9dd6
have 4 foldMaps; two right, two left, two lazy, two strict, red fish,…
chessai Sep 17, 2018
8aaa9d1
bump quickcheck-classes for travis happiness
chessai Sep 17, 2018
96eb0cc
change fold{dir}MapPrimArray to foldMap{dir}PrimArray, and mention al…
chessai Sep 18, 2018
534a20c
provide an example to demonstrate association and accumulation, corre…
chessai Sep 18, 2018
6f0c84e
simplify examples for foldMapRPrimArray foldMapLPrimArray
chessai Sep 18, 2018
d4eb3d0
make strict foldMaps on PrimArray force function value at each step
chessai Sep 18, 2018
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30 changes: 30 additions & 0 deletions Data/Primitive/PrimArray.hs
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Expand Up @@ -66,6 +66,10 @@ module Data.Primitive.PrimArray
, foldlPrimArray
, foldlPrimArray'
, foldlPrimArrayM'
, foldrMapPrimArray
, foldlMapPrimArray
, foldrMapPrimArray'
, foldlMapPrimArray'
-- * Effectful Folding
, traversePrimArray_
, itraversePrimArray_
Expand Down Expand Up @@ -467,6 +471,32 @@ sizeofPrimArray :: forall a. Prim a => PrimArray a -> Int
{-# INLINE sizeofPrimArray #-}
sizeofPrimArray (PrimArray arr#) = I# (quotInt# (sizeofByteArray# arr#) (sizeOf# (undefined :: a)))

-- | Map each element of the primitive array to a monoid, and combine the results.
-- The combination is right-associated, and the accumulation is lazy.
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foldrMapPrimArray :: forall a m. (Prim a, Monoid m) => (a -> m) -> PrimArray a -> m
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I'd rather see the Map before the r.

{-# INLINE foldrMapPrimArray #-}
foldrMapPrimArray f = foldrPrimArray (\a acc -> f a `mappend` acc) mempty

-- | Map each element of the primitive array to a monoid, and combine the results.
-- The combination is left-associated, and the accumulation is lazy.
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foldlMapPrimArray :: forall a m. (Prim a, Monoid m) => (a -> m) -> PrimArray a -> m
{-# INLINE foldlMapPrimArray #-}
foldlMapPrimArray f = foldlPrimArray (\acc a -> acc `mappend` f a) mempty

-- | Map each element of the primitive array to a monoid, and combine the results.
-- The combination is right-associated, and the accumulation is strict, though
-- this function is not necessarily strict in its result.
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"This function is not necessarily strict in its result" doesn't mean anything whatsoever to me. What I meant needed explanation is that at each step, we force the accumulator value, but we don't force the value of f a. So if mappend is lazy in its first argument, f a will not be evaluated. This is probably the correct behavior, but needs better explanation.

foldrMapPrimArray' :: forall a m. (Prim a, Monoid m) => (a -> m) -> PrimArray a -> m
{-# INLINE foldrMapPrimArray' #-}
foldrMapPrimArray' f = foldrPrimArray (\a !acc -> f a `mappend` acc) mempty

-- | Map each element of the primitive array to a monoid, and combine the results.
-- The combination is left-associated, and the accumulation is strict, though
-- this function is not necessarily strict in its result.
foldlMapPrimArray' :: forall a m. (Prim a, Monoid m) => (a -> m) -> PrimArray a -> m
{-# INLINE foldlMapPrimArray' #-}
foldlMapPrimArray' f = foldlPrimArray (\ !acc a -> acc `mappend` f a) mempty

-- | Lazy right-associated fold over the elements of a 'PrimArray'.
{-# INLINE foldrPrimArray #-}
foldrPrimArray :: forall a b. Prim a => (a -> b -> b) -> b -> PrimArray a -> b
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4 changes: 3 additions & 1 deletion changelog.md
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Expand Up @@ -29,7 +29,9 @@

## Changes in version 0.6.4.1

* Add instances for the following newtypes from `base`:
* Add `foldMapPrimArray` and `foldMapPrimArray'`
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This needs to be updated now that you've added more functions.


* Add `Prim` instances for the following newtypes from `base`:
`Const`, `Identity`, `Down`, `Dual`, `Sum`, `Product`,
`First`, `Last`, `Min`, `Max`

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2 changes: 1 addition & 1 deletion test/primitive-tests.cabal
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Expand Up @@ -38,7 +38,7 @@ test-suite test
, tasty-quickcheck
, tagged
, transformers >= 0.3
, quickcheck-classes >= 0.4.11.1
, quickcheck-classes >= 0.4.14.2
ghc-options: -O2

source-repository head
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