Data.Some

Documentation

data Some tag where

Existential. This is type is useful to hide GADTs' parameters.

>>> data Tag :: * -> * where TagInt :: Tag Int; TagBool :: Tag Bool
>>> instance GShow Tag where gshowsPrec _ TagInt = showString "TagInt"; gshowsPrec _ TagBool = showString "TagBool"

You can either use PatternSynonyms

>>> let x = Some TagInt
>>> x
Some TagInt

>>> case x of { Some TagInt -> "I"; Some TagBool -> "B" } :: String
"I"

or you can use functions

>>> let y = mkSome TagBool
>>> y
Some TagBool

>>> withSome y $ \y' -> case y' of { TagInt -> "I"; TagBool -> "B" } :: String
"B"

The implementation of mapSome is safe.

>>> let f :: Tag a -> Tag a; f TagInt = TagInt; f TagBool = TagBool
>>> mapSome f y
Some TagBool

but you can also use:

>>> withSome y (mkSome . f)
Some TagBool

Bundled Patterns

pattern Some :: tag a -> Some tag

pattern This :: tag a -> Some tag

Deprecated: Use Some instead

Instances

GEq tag => Eq (Some tag)

Defined in Data.Some

Methods

(==) :: Some tag -> Some tag -> Bool

(/=) :: Some tag -> Some tag -> Bool

GCompare tag => Ord (Some tag)

Defined in Data.Some

Methods

compare :: Some tag -> Some tag -> Ordering

(<) :: Some tag -> Some tag -> Bool

(<=) :: Some tag -> Some tag -> Bool

(>) :: Some tag -> Some tag -> Bool

(>=) :: Some tag -> Some tag -> Bool

max :: Some tag -> Some tag -> Some tag

min :: Some tag -> Some tag -> Some tag

GRead f => Read (Some f)

Defined in Data.Some

Methods

readsPrec :: Int -> ReadS (Some f)

readList :: ReadS [Some f]

readPrec :: ReadPrec (Some f)

readListPrec :: ReadPrec [Some f]

GShow tag => Show (Some tag)

Defined in Data.Some

Methods

showsPrec :: Int -> Some tag -> ShowS

show :: Some tag -> String

showList :: [Some tag] -> ShowS

mkSome :: tag a -> Some tag

Constructor.

withSome :: Some tag -> (forall a. tag a -> b) -> b

Eliminator.

mapSome :: (forall t. f t -> g t) -> Some f -> Some g