Control.Applicative.Alternative

Partial maps and filters over Alternative instances.

This is considerably weaker than MonadPlus, as we have no possibility of removing intermediate structure, as in mcatMaybes.

Basics

module Control.Applicative

asum :: (Foldable t, Alternative f) => t (f a) -> f a

The sum of a collection of actions, generalizing concat.

asum is just like msum, but generalised to Alternative.

Examples

Basic usage:

>>> asum [Just "Hello", Nothing, Just "World"]
Just "Hello"

Constructing

afold :: (Alternative f, Foldable t) => t a -> f a

Fold a value into an arbitrary MonadPlus type.

This function generalizes the toList function.

afromList :: Alternative f => [a] -> f a

This function generalizes the listToMaybe function.

afromMaybe :: Alternative f => Maybe a -> f a

Translate maybe to an arbitrary Alternative type.

This function generalizes the maybeToList function.