Data.Maybe

Prelude Data.Maybe> maybe "" show (Just 5)

"5"

Prelude Data.Maybe> maybe "" show Nothing

""

Prelude Data.Maybe> isJust (Just 3)

True

Prelude Data.Maybe> isJust Nothing

False

Prelude Data.Maybe> isNothing (Just 3)

False

Prelude Data.Maybe> isNothing Nothing

True

Prelude Data.Maybe> fromJust (Just 1)

1

Prelude Data.Maybe> 2 * (fromJust Nothing)

*** Exception: Maybe.fromJust: Nothing

Prelude Data.Maybe> fromMaybe "" (Just "Hello, World!")

"Hello, World!"

Prelude Data.Maybe> fromMaybe "" Nothing

""

Prelude Data.Maybe> listToMaybe []

Nothing

Prelude Data.Maybe> listToMaybe [1,2,3]

Just 1

Prelude Data.Maybe> maybeToList (Just 7)

[7]

Prelude Data.Maybe> maybeToList Nothing

[]

Prelude Data.Maybe> catMaybes [Just 1, Nothing, Just 3]

[1,3]

Prelude Data.Maybe> let readMaybeInt = Text.Read.readMaybe :: String -> Maybe Int

Prelude Data.Maybe> mapMaybe readMaybeInt ["1", "Foo", "3"]

[1,3]

Data.Either

Prelude Data.Either> either length (*2) $ Left "foo"

3

Prelude Data.Either> either length (*2) $ Right 3

6

Prelude Data.Either> lefts [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]

["foo","bar","baz"]

Prelude Data.Either> rights [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]

[3,7]

Prelude Data.Either> isLeft (Left "foo")

True

Prelude Data.Either> isLeft (Right 3)

False

Prelude Data.Either> isRight (Left "foo")

False

Prelude Data.Either> isRight (Right 3)

True

Prelude Data.Either> fromLeft 1 (Left 3)

3

Prelude Data.Either> fromLeft 1 (Right "foo")

1

Prelude Data.Either> fromRight 1 (Right 3)

3

Prelude Data.Either> fromRight 1 (Left "foo")

1

Prelude Data.Either> partitionEithers [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]

(["foo","bar","baz"],[3,7])

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