Safe Haskell | None |
---|---|

Language | Haskell98 |

Maybe functions.

## Synopsis

- isJust :: Maybe a -> Bool
- isNothing :: Maybe a -> Bool
- fromJust :: Maybe a -> a
- fromMaybe :: a -> Maybe a -> a
- maybeToList :: Maybe a -> [a]
- listToMaybe :: [a] -> Maybe a
- catMaybes :: [Maybe a] -> [a]
- mapMaybe :: (a -> Maybe b) -> [a] -> [b]
- mapMaybeFB :: (b -> r -> r) -> (a -> Maybe b) -> a -> r -> r
- whenJust :: Maybe a -> (a -> Fay ()) -> Fay ()
- whenJust' :: Maybe a -> (a -> Fay b) -> Fay (Maybe b)
- onJust :: (a -> b) -> Maybe a -> Maybe b
- joinMaybe :: Maybe (Maybe a) -> Maybe a

# General operations from base

maybeToList :: Maybe a -> [a] Source #

The `maybeToList`

function returns an empty list when given
`Nothing`

or a singleton list when not given `Nothing`

.

listToMaybe :: [a] -> Maybe a Source #

The `listToMaybe`

function returns `Nothing`

on an empty list
or

where `Just`

a`a`

is the first element of the list.

mapMaybeFB :: (b -> r -> r) -> (a -> Maybe b) -> a -> r -> r Source #