Generate fields only if they make sense for the given era #40
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| @@ -0,0 +1,88 @@ | ||
| {-# LANGUAGE GADTs #-} | ||
| {-# LANGUAGE KindSignatures #-} | ||
| {-# LANGUAGE LambdaCase #-} | ||
| {-# LANGUAGE ScopedTypeVariables #-} | ||
| {-# LANGUAGE StandaloneDeriving #-} | ||
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| module Cardano.Api.Feature | ||
| ( FeatureValue (..) | ||
| , FeatureInEra(..) | ||
| , featureInShelleyBasedEra | ||
| , valueOrDefault | ||
| , asFeatureValue | ||
| , asFeatureValueInShelleyBasedEra | ||
| , isFeatureValue | ||
| ) where | ||
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| import Cardano.Api.Eras | ||
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| import Data.Kind | ||
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| -- | A class for features that are supported in some eras but not others. | ||
| class FeatureInEra (feature :: Type -> Type) where | ||
| -- | Determine the value to use for a feature in a given 'CardanoEra'. | ||
| -- Note that the negative case is the first argument, and the positive case is the second as per | ||
| -- the 'either' function convention. | ||
| featureInEra :: () | ||
| => a -- ^ Value to use if the feature is not supported in the era | ||
| -> (feature era -> a) -- ^ Function to get thealue to use if the feature is supported in the era | ||
| -> CardanoEra era -- ^ Era to check | ||
| -> a -- ^ The value to use | ||
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| -- | Determine the value to use for a feature in a given 'ShelleyBasedEra'. | ||
| featureInShelleyBasedEra :: () | ||
| => FeatureInEra feature | ||
| => a | ||
| -> (feature era -> a) | ||
| -> ShelleyBasedEra era | ||
| -> a | ||
| featureInShelleyBasedEra no yes = featureInEra no yes . shelleyBasedToCardanoEra | ||
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| -- | A value of type @'FeatureValue' feature era a@ is either: | ||
| data FeatureValue feature era a where | ||
| -- | A value is available for this feature in this era | ||
| FeatureValue | ||
| :: feature era | ||
| -- ^ The witness that the feature is supported in this era | ||
| -> a | ||
| -- ^ The value to use | ||
| -> FeatureValue feature era a | ||
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| -- | No value is available for this feature in this era | ||
| NoFeatureValue | ||
| :: FeatureValue feature era a | ||
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| deriving instance (Eq a, Eq (feature era)) => Eq (FeatureValue feature era a) | ||
| deriving instance (Show a, Show (feature era)) => Show (FeatureValue feature era a) | ||
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| -- | Determine if a value is defined. | ||
| -- | ||
| -- If the value is not defined, it could be because the feature is not supported or | ||
| -- because the feature is supported but the value is not available. | ||
| isFeatureValue :: FeatureValue feature era a -> Bool | ||
| isFeatureValue = \case | ||
| NoFeatureValue -> False | ||
| FeatureValue _ _ -> True | ||
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| -- | Get the value if it is defined, otherwise return the default value. | ||
| valueOrDefault :: a -> FeatureValue feature era a -> a | ||
| valueOrDefault defaultValue = \case | ||
| NoFeatureValue -> defaultValue | ||
| FeatureValue _ a -> a | ||
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| -- | Attempt to construct a 'FeatureValue' from a value and era. | ||
| -- If the feature is not supported in the era, then 'NoFeatureValue' is returned. | ||
| asFeatureValue :: () | ||
| => FeatureInEra feature | ||
| => a | ||
| -> CardanoEra era | ||
| -> FeatureValue feature era a | ||
| asFeatureValue value = featureInEra NoFeatureValue (`FeatureValue` value) | ||
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| -- | Attempt to construct a 'FeatureValue' from a value and a shelley-based-era. | ||
| asFeatureValueInShelleyBasedEra :: () | ||
| => FeatureInEra feature | ||
| => a | ||
| -> ShelleyBasedEra era | ||
| -> FeatureValue feature era a | ||
| asFeatureValueInShelleyBasedEra value = asFeatureValue value . shelleyBasedToCardanoEra |
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This function is not yet used because the relevant fields are not yet using the
FeatureValuetype, but it will be once that change is made (possibly in a future PR).The advantage of having a
genFeatureValueInErais that using it is less error prone than exist practise which is to define per-feature generators manually. It is very easy to accidentally not returnNoFeatureValuein the case where the feature is supported in the given era in implementation of those manually written functions and that bug currently exists in the code.