Portability | non-portable (GHC Extensions) |
---|---|
Stability | experimental |
Maintainer | Patrick Bahr <paba@diku.dk> |
Safe Haskell | Safe-Inferred |
This module provides functionality to number the components of a functorial value with consecutive integers.
- newtype Numbered a = Numbered (Int, a)
- unNumbered :: Numbered a -> a
- number :: Traversable f => f a -> f (Numbered a)
- class (Functor t, Foldable t) => Traversable t
Documentation
This type is used for numbering components of a functorial value.
unNumbered :: Numbered a -> aSource
number :: Traversable f => f a -> f (Numbered a)Source
This function numbers the components of the given functorial value with consecutive integers starting at 0.
class (Functor t, Foldable t) => Traversable t
Functors representing data structures that can be traversed from left to right.
Minimal complete definition: traverse
or sequenceA
.
Instances are similar to Functor
, e.g. given a data type
data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
a suitable instance would be
instance Traversable Tree where traverse f Empty = pure Empty traverse f (Leaf x) = Leaf <$> f x traverse f (Node l k r) = Node <$> traverse f l <*> f k <*> traverse f r
This is suitable even for abstract types, as the laws for <*>
imply a form of associativity.
The superclass instances should satisfy the following:
- In the
Functor
instance,fmap
should be equivalent to traversal with the identity applicative functor (fmapDefault
). - In the
Foldable
instance,foldMap
should be equivalent to traversal with a constant applicative functor (foldMapDefault
).
Traversable [] | |
Traversable Maybe | |
Traversable Identity | |
Ix i => Traversable (Array i) | |
Traversable (Map k) | |
Traversable f => Traversable (ListT f) | |
Traversable f => Traversable (MaybeT f) | |
Traversable f => Traversable (IdentityT f) | |
Traversable f => Traversable (ErrorT e f) | |
Traversable f => Traversable (WriterT w f) | |
Traversable f => Traversable (WriterT w f) | |
(Traversable f, Traversable g) => Traversable (Compose f g) | |
Traversable f => Traversable (:&: f a) | |
(Traversable f, Traversable g) => Traversable (:+: f g) | |
Traversable f => Traversable (Cxt h f) |