Skulk.Outcome

Universal result type for calculations that may either: produce a value, signal the failure to obtain value, or signal that value is "not interesting".

Documentation

data Outcome a

Universal result type for calculations that may either: produce a value, signal the failure to obtain value, or signal that value is "not interesting".

E.g. a text parser distinguishes situations when text file is "structured enough" to have a syntax error (that's Fail) and when text file is not in a supported format at all (that's Skip).

Constructors

OK a

Result value.

Fail String

Failed to obtain value because of particular reason.

Skip String

Depending on context, it's might be "no action required" or "no action taken" because of particular reason.

Instances

Monad Outcome

Methods

(>>=) :: Outcome a -> (a -> Outcome b) -> Outcome b

(>>) :: Outcome a -> Outcome b -> Outcome b

return :: a -> Outcome a

fail :: String -> Outcome a

Functor Outcome

Methods

fmap :: (a -> b) -> Outcome a -> Outcome b

(<$) :: a -> Outcome b -> Outcome a

Applicative Outcome

Methods

pure :: a -> Outcome a

(<*>) :: Outcome (a -> b) -> Outcome a -> Outcome b

(*>) :: Outcome a -> Outcome b -> Outcome b

(<*) :: Outcome a -> Outcome b -> Outcome a

Foldable Outcome

Methods

fold :: Monoid m => Outcome m -> m

foldMap :: Monoid m => (a -> m) -> Outcome a -> m

foldr :: (a -> b -> b) -> b -> Outcome a -> b

foldr' :: (a -> b -> b) -> b -> Outcome a -> b

foldl :: (b -> a -> b) -> b -> Outcome a -> b

foldl' :: (b -> a -> b) -> b -> Outcome a -> b

foldr1 :: (a -> a -> a) -> Outcome a -> a

foldl1 :: (a -> a -> a) -> Outcome a -> a

toList :: Outcome a -> [a]

null :: Outcome a -> Bool

length :: Outcome a -> Int

elem :: Eq a => a -> Outcome a -> Bool

maximum :: Ord a => Outcome a -> a

minimum :: Ord a => Outcome a -> a

sum :: Num a => Outcome a -> a

product :: Num a => Outcome a -> a

Traversable Outcome

Methods

traverse :: Applicative f => (a -> f b) -> Outcome a -> f (Outcome b)

sequenceA :: Applicative f => Outcome (f a) -> f (Outcome a)

mapM :: Monad m => (a -> m b) -> Outcome a -> m (Outcome b)

sequence :: Monad m => Outcome (m a) -> m (Outcome a)

Eq a => Eq (Outcome a)

Methods

(==) :: Outcome a -> Outcome a -> Bool

(/=) :: Outcome a -> Outcome a -> Bool

Show a => Show (Outcome a)

Methods

showsPrec :: Int -> Outcome a -> ShowS

show :: Outcome a -> String

showList :: [Outcome a] -> ShowS

describe :: (a -> String) -> Outcome a -> String

Renders Outcome to String using provided function to render the OKs.

toEither :: Outcome a -> Either String a

Converts Outcome into either wrapped value or error message.

fromEither :: Either String a -> Outcome a

Converts `Either ErrorMessage Value` to `Outcome Value`

fromMaybe :: String -> Maybe a -> Outcome a

Converts `Maybe Value` to `Outcome Value` using provided error message to designate Fail.

allOK :: [Outcome a] -> Outcome [a]

Collapses a list of Outcomes into a single Outcome. Result may either be Fail (if original list contains any) or list of all OKs; all Skips are discarded.

exposeOrDie :: Outcome a -> a

Either returns a wrapped value or prints out an error message and terminates the execution with error.

type OutcomeM a b = Deep a Outcome b

type OutcomeIO a = OutcomeM IO a

describeAndPrint :: (a -> String) -> OutcomeIO a -> IO ()