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  1. ByMaybeAttr :: WhyNullable

    persistent Database.Persist.Types

    No documentation available.

  2. FieldAttrMaybe :: FieldAttr

    persistent Database.Persist.Types

    The Maybe keyword goes after the type. This indicates that the column is nullable, and the generated Haskell code will have a Maybe type for it. Example: 

    User
name Text Maybe

  3. flagToMaybe :: Flag a -> Maybe a

    Cabal Distribution.Simple.Flag

    Converts a Flag value to a Maybe value.

  4. userMaybeSpecifyPath :: String -> Maybe FilePath -> ProgramDb -> ProgramDb

    Cabal Distribution.Simple.Program

    No documentation available.

  5. userMaybeSpecifyPath :: String -> Maybe FilePath -> ProgramDb -> ProgramDb

    Cabal Distribution.Simple.Program.Db

    No documentation available.

  6. flagToMaybe :: Flag a -> Maybe a

    Cabal Distribution.Simple.Setup

    Converts a Flag value to a Maybe value.

  7. installMaybeExecutableFile :: Verbosity -> FilePath -> FilePath -> IO ()

    Cabal Distribution.Simple.Utils

    Install a file that may or not be executable, preserving permissions.

  8. installMaybeExecutableFiles :: Verbosity -> FilePath -> [(FilePath, FilePath)] -> IO ()

    Cabal Distribution.Simple.Utils

    This is like copyFiles but uses installMaybeExecutableFile.

  9. lookupMaybe :: Text -> Form -> Either Text (Maybe Text)

    http-api-data Web.FormUrlEncoded

    Lookup an optional value for a key. Fail if there is more than one value. 

    >>> lookupMaybe "name" []
Right Nothing

>>> lookupMaybe "name" [("name", "Oleg")]
Right (Just "Oleg")

>>> lookupMaybe "name" [("name", "Oleg"), ("name", "David")]
Left "Duplicate key \"name\""

  10. parseMaybe :: FromHttpApiData v => Text -> Form -> Either Text (Maybe v)

    http-api-data Web.FormUrlEncoded

    Lookup an optional value for a given key and parse it with parseQueryParam. Fail if there is more than one value for the key. 

    >>> parseMaybe "age" [] :: Either Text (Maybe Word8)
Right Nothing

>>> parseMaybe "age" [("age", "12"), ("age", "25")] :: Either Text (Maybe Word8)
Left "Duplicate key \"age\""

>>> parseMaybe "age" [("age", "seven")] :: Either Text (Maybe Word8)
Left "could not parse: `seven' (input does not start with a digit)"

>>> parseMaybe "age" [("age", "777")] :: Either Text (Maybe Word8)
Left "out of bounds: `777' (should be between 0 and 255)"

>>> parseMaybe "age" [("age", "7")] :: Either Text (Maybe Word8)
Right (Just 7)

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