#Unfoldable1 Source

class 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.



#replicate1 Source

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)

#replicate1A Source

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))

#singleton Source

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

Contain a single value. For example:

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

#range Source

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)