Haskell List of tuples to list?

Question

Is it possible to convert a list of tuples [(Int,Int)] as a generic way which valid to any input size ? .. i saw in various questions thats its not possible gen

Answer 1

The lens library handles this and similar cases consistently.

> import Control.Lens
> toListOf (traverse . both) [(1,2),(3,4)]
            ^          ^
            |          |> Traversal of the tuple (a, a)
            |> Traversal of a list [b]
[1,2,3,4]

To convert from a list of lists:

> toListOf (traverse . traverse) [[1,2],[3,4],[5,6,7]]
[1,2,3,4,5,6,7]

addition edit:

traverse works with Traversable

traverse will work with any datatype that has a Traversable instance, for example trees.

> import Data.Tree
> let t = Node 1 [Node 2 [Node 3 [], Node 4 []], Node 5 []]
> let prettyTree = drawTree . fmap show
> prettyTree t
1
|
+- 2
|  |
|  +- 3
|  |
|  `- 4
|
`- 5
> toListOf (traverse . traverse) [t, t]
[1,2,3,4,5,1,2,3,4,5]