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Deprecate dot #75

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Merged
merged 2 commits into from
May 3, 2025
Merged

Deprecate dot #75

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2878498
Fix dot documentation
konsumlamm Apr 23, 2025
046c791
Deprecate `dot`
konsumlamm Apr 24, 2025
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31 changes: 16 additions & 15 deletions Control/Parallel/Strategies.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -358,20 +358,24 @@ x `usingIO` strat = runEvalIO (strat x)
withStrategyIO :: Strategy a -> a -> IO a
withStrategyIO = flip usingIO

-- | Compose two strategies sequentially.
-- This is the analogue to function composition on strategies.
-- | Compose two strategies.
--
-- For any strategies @strat1@, @strat2@, and @strat3@,
-- > strat2 `dot` strat1 == strat2 . withStrategy strat1
--
-- 'dot' is associative:
--
-- > (strat1 `dot` strat2) `dot` strat3 == strat1 `dot` (strat2 `dot` strat3)
-- > strat1 `dot` strat1 = strat1
-- > strat1 `dot` r0 == strat1
--
-- > strat2 `dot` strat1 == strat2 . withStrategy strat1
-- 'r0' and 'rseq' are one-sided identities of 'dot':
--
-- > strat `dot` r0 == strat
-- > strat `dot` rseq == strat
{-# DEPRECATED dot "'dot' is an unintuitive composition operator. Use 'Control.Monad.<=<` instead." #-}
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Plus one for deprecating dot.

dot :: Strategy a -> Strategy a -> Strategy a
strat2 `dot` strat1 = strat2 . runEval . strat1

-- Note [dot proofs]
-- ~~~~~~~~~~~~~~~~~
-- Proof of strat2 `dot` strat1 == strat2 . withStrategy strat1
--
-- strat2 . withStrategy strat1
Expand All @@ -380,17 +384,14 @@ strat2 `dot` strat1 = strat2 . runEval . strat1
-- == \x -> strat2 (runEval (strat1 x))
-- == \x -> (strat2 . runEval . strat1) x
-- == strat2 `dot` strat1

-- One might be tempted to think that 'dot' is equivalent to '(<=<)',
-- the right-to-left Kleisli composition in the Eval monad, because
-- '(<=<)' can take the type @Strategy a -> Strategy a -> Strategy a@
-- and intuitively does what 'dot' does: First apply the strategy to the
-- right then the one to the left. However, there is a subtle difference
-- in strictness, witnessed by the following example:
--
-- > (r0 `dot` rseq) undefined == Done undefined
-- > (r0 <=< rseq) undefined == undefined
-- Proof of associativity
--
-- (strat1 `dot` strat2) `dot` strat3
-- == (strat1 . runEval . strat2) . runEval . strat3
-- == strat1 . runEval . strat2 . runEval . strat3
-- == strat1 . runEval . (strat2 . runEval . strat3)
-- == strat1 `dot` (strat2 `dot` strat3)

-- | Inject a sequential strategy (i.e., coerce a sequential strategy
-- to a general strategy).
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