Data.Unfolder

Unfolders provide a way to unfold data structures. They are applicative functors that can perform a choice. (Which is basically Alternative without empty.)

Unfolder

class Applicative f => Unfolder f where

Unfolders provide a way to unfold data structures. The minimal implementation is choose.

Methods

choose :: [f x] -> f x

Choose one of the values from the list.

chooseInt :: Int -> f Int

Given a number n, return a number between '0' and 'n - 1'.

Instances

Unfolder []

Don't choose but return all items.

Unfolder Right

Always choose the last item.

Unfolder Left

Always choose the first item.

Unfolder m => Unfolder (Reverse m)

Applicative f => Unfolder (BFS f)

Choose between values of a given depth only.

(Monad m, Unfolder m) => Unfolder (StateT s m)

Unfolder m => Unfolder (ReaderT r m)

Unfolder m => Unfolder (ContT r m)

(Unfolder p, Applicative q) => Unfolder (Compose p q)

(Unfolder p, Unfolder q) => Unfolder (Product p q)

(Functor m, Monad m, RandomGen g) => Unfolder (Random g m)

Choose randomly.

chooseAltDefault :: (Alternative f, Unfolder f) => [f x] -> f x

If an unfolder is an instance of Alternative, choose can be implemented in terms of <|>.

chooseMonadDefault :: (Monad m, Unfolder m) => [m x] -> m x

If an unfolder is monadic, choose can be implemented in terms of chooseInt.

boundedEnum :: forall f a. (Unfolder f, Bounded a, Enum a) => f a

If a datatype is bounded and enumerable, we can use chooseInt to generate a value.

Unfolder instances

newtype Left x

Constructors

L

Fields

getL :: Identity x

Instances

Monad Left

Functor Left

Applicative Left

Unfolder Left

Always choose the first item.

newtype Right x

Constructors

R

Fields

getR :: Identity x

Instances

Monad Right

Functor Right

Applicative Right

Unfolder Right

Always choose the last item.

newtype Random g m a

Constructors

Random

Fields

getRandom :: StateT g m a

Instances

Monad m => Monad (Random g m)

Functor m => Functor (Random g m)

(Monad m, Functor m) => Applicative (Random g m)

(Functor m, Monad m, RandomGen g) => Unfolder (Random g m)

Choose randomly.

newtype BFS f x

Return a generator of values of a given depth. Returns Nothing if there are no values of that depth or deeper.

Constructors

BFS

Fields

getBFS :: Int -> Maybe [f x]

Instances

Functor f => Functor (BFS f)

Applicative f => Applicative (BFS f)

Applicative f => Unfolder (BFS f)

Choose between values of a given depth only.

runBFS :: Unfolder f => BFS f x -> f x

packBFS :: f x -> BFS f x