Retrieve the constructor name of the given value as a string. This implementation is taken from https://stackoverflow.com/questions/48179380/getting-the-data-constructor-name-as-a-string-using-ghc-generics .

Automatically derived from Generic instances.

Type that can be reduced away from a constructor. Use this to make your data types compatible. The reduction process and the (=?=)-operator do not evaluate fields, therefore creating an empty instance which defaults to reduceWith = undefined is okay as long as no reduced field of this type is strict.

Reduction of a constructor a -> ... -> c to a value of type c.

Checks whether two values are created by the same data constructor. Also works with constructors that have not yet received all their arguments. This allows for very convenient constructs, e.g.:

>>> Just 1 =?= Just
True

>>> Just 1 =?= Nothing
False

>>> let filterJust = filter (=?= Just)
>>> filterJust [Just 1, Nothing, Just 9001]
[Just 1, Just 9001]

>>> let filterJust_ = mapMaybe $ (=?= Just) ==> fromJust
>>> filterJust_ [Just 1, Nothing, Just 9001]
[1, 9001]

>>> let over9000 = mapMaybe $ ((=?= Just) <&&> (>9000) . fromJust) ==> fromJust
>>> over9000 [Just 1, Nothing, Just 9001]
[9001]

(pred ==> f) x returns Just (f x) if pred x succeeds and Nothing otherwise.

Adds negative and positive infinity to an ordered type. The fromEnum function is inherently susceptible to overflow since the class Enum is defined using Int instead of Integer, but this should not cause trouble with "small" enums.

The mapMaybe function is a version of map which can throw out elements. In particular, the functional argument returns something of type Maybe b. If this is Nothing, no element is added on to the result list. If it is Just b, then b is included in the result list.

Examples

>>> import Text.Read ( readMaybe )
>>> let readMaybeInt = readMaybe :: String -> Maybe Int
>>> mapMaybe readMaybeInt ["1", "Foo", "3"]
[1,3]
>>> catMaybes $ map readMaybeInt ["1", "Foo", "3"]
[1,3]

>>> mapMaybe Just [1,2,3]
[1,2,3]