Data.Maybe

v11.3.15 • Optional Values

The Maybe type represents optional values. A value of type Maybe A either contains a value of type A (represented as Just x), or it is empty (represented as Nothing).

Types

Maybe :: * -> *

The Maybe type represents optional values.

Implementation

data Maybe A = Nothing | Just A

Foreigns

No foreign functions defined in this module.

Functions

maybe :: B -> (A -> B) -> Maybe A -> B

A common pattern to handle Maybe values by providing a default and a function.

Implementation

maybe def f m = case m of
    Nothing -> def
    Just x  -> f x

from_maybe :: A -> Maybe A -> A

Extracts the value from a Maybe, returning the default if it's Nothing.

Implementation

from_maybe def m = case m of
    Nothing -> def
    Just x  -> x

is_nothing :: Maybe A -> Bool

Returns True if the value is Nothing.

Implementation

is_nothing m = case m of
    Nothing -> True
    Just x  -> False

is_just :: Maybe A -> Bool

Returns True if the value contains a result.

Implementation

is_just m = case m of
    Nothing -> False
    Just x  -> True