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

[Graham Gill]

What about just

map (map f) xxs

where for your example

xxs == [[1,2], [3,4]]
f == (+1)

Graham

On 13/08/2012 1:21 AM, Christopher Howard wrote:
> Hi. Is the some generic, clean syntax to unwrap a nested list, modify
> the value, and put it back together? 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]].
>
> After reading about the list monad, I was rather excited, because I
> (mistakenly) thought something like this would work:
>
> code:
> --------
> a = do b <- [[1,2],[3,4]]
>         c <- b
>         return (c + 1)
> --------
>
> That would be awesome, because I would be able to modify the list at
> each level of unwrapping, while leaving the code very neat and readable.
> However, what the above example actually does is produce a /single/ list
> from the values:
>
> code:
> --------
> *Main> a
> [2,3,4,5]
> --------
>
> Obviously wishing won't change how the list monad works, but I thought
> it might be worth asking if there is some other monad or syntactic trick
> that does something along the lines of what I am looking for.
>
>
>
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