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Fancy rules for traversing with PrimMonad #146

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Fancy rules for traversing with PrimMonad #146

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3d5abaa
Fancy rules for traversing with PrimMonad
treeowl Apr 24, 2018
7f38887
Simplify; remove some extensions
treeowl Apr 24, 2018
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42 changes: 31 additions & 11 deletions Data/Primitive/Array.hs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
{-# LANGUAGE CPP, MagicHash, UnboxedTuples, DeriveDataTypeable, BangPatterns #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE GADTs, ConstraintKinds #-}

-- |
-- Module : Data.Primitive.Array
Expand Down Expand Up @@ -73,6 +74,9 @@ import Text.ParserCombinators.ReadP
#if MIN_VERSION_base(4,9,0) || MIN_VERSION_transformers(0,4,0)
import Data.Functor.Classes (Eq1(..),Ord1(..),Show1(..),Read1(..))
#endif
import Control.Monad.Trans.Maybe
import Control.Monad.Trans.Identity
import Control.Monad.Trans.State.Strict

-- | Boxed arrays
data Array a = Array
Expand Down Expand Up @@ -520,18 +524,34 @@ traverseArray f = \ !ary ->
{-# INLINE [1] traverseArray #-}

{-# RULES
"traverse/ST" forall (f :: a -> ST s b). traverseArray f =
traverseArrayP f
"traverse/IO" forall (f :: a -> IO b). traverseArray f =
traverseArrayP f
"toWonk" [~1] traverseArray
= traverseArrayWonk (WonkP (\(Dict :: Dict (PrimMonad f)) (g :: a -> f b) -> traverseArrayP g))
"wonkIO" forall (w :: WonkP IO f).
traverseArrayWonk w = runWonkP w Dict
"wonkST" forall (w :: WonkP (ST s) f).
traverseArrayWonk w = runWonkP w Dict
"wonkMaybeT" forall (w :: WonkP (MaybeT m) f).
traverseArrayWonk w = traverseArrayWonk (WonkP (\(Dict :: Dict (PrimMonad m)) -> runWonkP w Dict))
"wonkStateT" forall (w :: WonkP (StateT s m) f).
traverseArrayWonk w = traverseArrayWonk (WonkP (\(Dict :: Dict (PrimMonad m)) -> runWonkP w Dict))
"wonkIdentityT" forall (w :: WonkP (IdentityT m) f).
traverseArrayWonk w = traverseArrayWonk (WonkP (\(Dict :: Dict (PrimMonad m)) -> runWonkP w Dict))
#-}
#if MIN_VERSION_base(4,8,0)
{-# RULES
"traverse/Id" forall (f :: a -> Identity b). traverseArray f =
(coerce :: (Array a -> Array (Identity b))
-> Array a -> Identity (Array b)) (fmap f)
#-}
#endif

data Dict c where
Dict :: c => Dict c

newtype WonkP m f = WonkP
{ runWonkP :: forall a b. Dict (PrimMonad m) -> (a -> f b) -> Array a -> f (Array b) }

traverseArrayWonk
:: Applicative f
=> WonkP m f
-> (a -> f b)
-> Array a
-> f (Array b)
traverseArrayWonk _ f = traverseArray f
{-# INLINE [0] traverseArrayWonk #-}
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Note: if it would help, we could add another wonky parameter to this function to handle Maybe, Either, Identity, and the like. I just haven't yet been able to figure out how that part should work at all.


-- | This is the fastest, most straightforward way to traverse
-- an array, but it only works correctly with a sufficiently
Expand Down