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DA.Either

The Either type represents values with two possibilities. It is sometimes used to represent a value which is either correct or an error. By convention, the Left constructor is used to hold an error value and the Right constructor is used to hold a correct value (mnemonic: “right” also means correct).

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Module Snapshot

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Functions

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lefts

lefts : [Either a b] -> [a] Extracts all the Left elements from a list.

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rights

rights : [Either a b] -> [b] Extracts all the Right elements from a list.

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partitionEithers

partitionEithers : [Either a b] -> ([a], [b]) Partitions a list of Either into two lists, the Left and Right elements respectively. Order is maintained.

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isLeft

isLeft : Either a b -> Bool Return True if the given value is a Left-value, False otherwise.

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isRight

isRight : Either a b -> Bool Return True if the given value is a Right-value, False otherwise.

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fromLeft

fromLeft : a -> Either a b -> a Return the contents of a Left-value, or a default value in case of a Right-value.

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fromRight

fromRight : b -> Either a b -> b Return the contents of a Right-value, or a default value in case of a Left-value.

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optionalToEither

optionalToEither : a -> Optional b -> Either a b Convert a Optional value to an Either value, using the supplied parameter as the Left value if the Optional is None.

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eitherToOptional

eitherToOptional : Either a b -> Optional b Convert an Either value to a Optional, dropping any value in Left.

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maybeToEither

maybeToEither : a -> Optional b -> Either a b

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eitherToMaybe

eitherToMaybe : Either a b -> Optional b