[Haskell-beginners] cleanest way to unwrap a list?

[Christopher Howard]

On 08/12/2012 09:37 PM, Shakthi Kannan wrote:
> Hi,
> 
> --- On Mon, Aug 13, 2012 at 10:51 AM, Christopher Howard
> <christopher.howard at frigidcode.com> wrote:
> | Say, for example, I have the list
> | [[1,2],[3,4]] and want to add 1 to each inner element, resulting in
> | [[2,3],[4,5]].
> \--
> 
> Like this?
> 
> ghci> let xxs = [[1,2], [3,4]]
> 
> ghci> [ [ x+1 | x <- xs] | xs <- xxs ]
> [[2,3],[4,5]]
> 
> SK
> 

Thanks everyone for the responses. I found the list comprehension
approach satisfactory, as it allows me to cleanly modify each layer of
the nested array as I unwrap it:

code:
--------
b = [[ x+1
    | x <- xs ++ [3] ]
    | xs <- [[1,2],[3,4]] ]

*Main> b
[[2,3,4],[4,5,4]]
--------

The only downside is that I have to write the layers out in reverse of
the way I would normally think of them, but that isn't too big of a
challenge.

I'm not sure how that would be done with map in a way that would be neat
and readable and wouldn't require declaring extra identifiers. I can't
give a fair evaluation of the Lens approach because I don't understand
enough of the theory yet.

-- 
frigidcode.com
indicium.us

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