class for toBson/fromBson, instances for Maybe
For example, you can now use fromBson of Maybe BsonValue (eg the result of a lookup) to convert to Maybe a. You can also give a Maybe a to toBson and for Nothing it will produce BsonNull and for Just a it will create the appropriate BsonValue for a.
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1 changed files with 20 additions and 4 deletions
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@ -261,11 +261,17 @@ putOutterObj bytes = do
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putDataType :: DataType -> Put
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putDataType = putI8 . fromDataType
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fromBson :: Convertible BsonValue a => BsonValue -> a
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fromBson = convert
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class BsonConv a b where
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fromBson :: Convertible a b => a -> b
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toBson :: Convertible b a => b -> a
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toBson :: Convertible a BsonValue => a -> BsonValue
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toBson = convert
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instance BsonConv BsonValue a where
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fromBson = convert
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toBson = convert
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instance BsonConv (Maybe BsonValue) (Maybe a) where
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fromBson = convert
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toBson = convert
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unsupportedError :: (Typeable a, Convertible BsonValue a) =>
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BsonValue -> ConvertResult a
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@ -343,6 +349,11 @@ instance Convertible Int32 BsonValue where
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instance Convertible Int64 BsonValue where
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safeConvert i = return $ BsonInt64 i
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instance (Convertible a BsonValue) =>
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Convertible (Maybe a) BsonValue where
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safeConvert Nothing = return BsonNull
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safeConvert (Just a) = safeConvert a
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instance Convertible BsonValue Double where
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safeConvert (BsonDouble d) = return d
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safeConvert (BsonInt32 i) = safeConvert i
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@ -426,3 +437,8 @@ instance Convertible BsonValue Int64 where
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safeConvert (BsonInt32 d) = safeConvert d
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safeConvert (BsonInt64 d) = return d
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safeConvert v = unsupportedError v
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instance (Convertible BsonValue a) =>
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Convertible (Maybe BsonValue) (Maybe a) where
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safeConvert Nothing = return Nothing
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safeConvert (Just a) = liftM Just $ safeConvert a
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