Refactor FirstToFinish and LastToFinish instances #3850
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Deriving a semigroup instance via 'Alt' for 'IO' relies on 'IO' 'Alternative' instance, which is not what we want. We want 'race` semantics instead. The drawback is that one needs to specify the 'Semigroup (FirstToFinish m a)' constraint, when 'm' is abstract, as in the tests.
coot
commented
Jun 27, 2023
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| instance Semigroup (FirstToFinish IO a) where | ||
| FirstToFinish a <> FirstToFinish b = FirstToFinish $ either id id <$> race a b |
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We can use similar approach to LastToFinish.
coot
commented
Jun 27, 2023
| , MonadTime m | ||
| , MonadTimer m | ||
| , MonadMask m | ||
| , forall a stm. stm ~ STM m => Semigroup (FirstToFinish stm a) |
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Use a type alias for this constraint if possible.
bolt12
reviewed
Oct 21, 2024
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The difference is explained here. |
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