Data.Unfoldable

class Unfoldable :: (Type -> Type) -> Constraintclass (Unfoldable1 t) <= Unfoldable t  where

This class identifies (possibly empty) data structures which can be unfolded.

The generating function f in unfoldr f is understood as follows:

• If f b is Nothing, then unfoldr f b should be empty.
• If f b is Just (Tuple a b1), then unfoldr f b should consist of a appended to the result of unfoldr f b1.

Note that it is not possible to give Unfoldable instances to types which represent structures which are guaranteed to be non-empty, such as NonEmptyArray: consider what unfoldr (const Nothing) should produce. Structures which are guaranteed to be non-empty can instead be given Unfoldable1 instances.

Members

• unfoldr :: forall a b. (b -> Maybe (Tuple a b)) -> b -> t a

Instances

• Unfoldable Array
• Unfoldable Maybe

replicate :: forall f a. Unfoldable f => Int -> a -> f a

Replicate a value some natural number of times. For example:

replicate 2 "foo" == (["foo", "foo"] :: Array String)

replicateA :: forall m f a. Applicative m => Unfoldable f => Traversable f => Int -> m a -> m (f a)

Perform an Applicative action n times, and accumulate all the results.

> replicateA 5 (randomInt 1 10) :: Effect (Array Int)
[1,3,2,7,5]

none :: forall f a. Unfoldable f => f a

The container with no elements - unfolded with zero iterations. For example:

none == ([] :: Array Unit)

fromMaybe :: forall f a. Unfoldable f => Maybe a -> f a

Convert a Maybe to any Unfoldable, such as lists or arrays.

fromMaybe (Nothing :: Maybe Int) == []
fromMaybe (Just 1) == [1]

class Unfoldable1 :: (Type -> Type) -> Constraintclass Unfoldable1 t  where

This class identifies data structures which can be unfolded.

The generating function f in unfoldr1 f corresponds to the uncons operation of a non-empty list or array; it always returns a value, and then optionally a value to continue unfolding from.

Note that, in order to provide an Unfoldable1 t instance, t need not be a type which is guaranteed to be non-empty. For example, the fact that lists can be empty does not prevent us from providing an Unfoldable1 List instance. However, the result of unfoldr1 should always be non-empty.

Every type which has an Unfoldable instance can be given an Unfoldable1 instance (and, in fact, is required to, because Unfoldable1 is a superclass of Unfoldable). However, there are types which have Unfoldable1 instances but cannot have Unfoldable instances. In particular, types which are guaranteed to be non-empty, such as NonEmptyList, cannot be given Unfoldable instances.

The utility of this class, then, is that it provides an Unfoldable-like interface while still permitting instances for guaranteed-non-empty types like NonEmptyList.

Members

• unfoldr1 :: forall a b. (b -> Tuple a (Maybe b)) -> b -> t a

Instances

• Unfoldable1 Array
• Unfoldable1 Maybe

singleton :: forall f a. Unfoldable1 f => a -> f a

Contain a single value. For example:

singleton "foo" == (NEL.singleton "foo" :: NEL.NonEmptyList String)

replicate1A :: forall m f a. Apply m => Unfoldable1 f => Traversable1 f => Int -> m a -> m (f a)

Perform an Apply action n times (at least once, so values n less than 1 will be treated as 1), and accumulate the results.

> replicate1A 2 (randomInt 1 10) :: Effect (NEL.NonEmptyList Int)
(NonEmptyList (NonEmpty 8 (2 : Nil)))
> replicate1A 0 (randomInt 1 10) :: Effect (NEL.NonEmptyList Int)
(NonEmptyList (NonEmpty 4 Nil))

replicate1 :: forall f a. Unfoldable1 f => Int -> a -> f a

Replicate a value n times. At least one value will be produced, so values n less than 1 will be treated as 1.

replicate1 2 "foo" == (NEL.cons "foo" (NEL.singleton "foo") :: NEL.NonEmptyList String)
replicate1 0 "foo" == (NEL.singleton "foo" :: NEL.NonEmptyList String)

range :: forall f. Unfoldable1 f => Int -> Int -> f Int

Create an Unfoldable1 containing a range of values, including both endpoints.

range 0 0 == (NEL.singleton 0 :: NEL.NonEmptyList Int)
range 1 2 == (NEL.cons 1 (NEL.singleton 2) :: NEL.NonEmptyList Int)
range 2 0 == (NEL.cons 2 (NEL.cons 1 (NEL.singleton 0)) :: NEL.NonEmptyList Int)