[Haskell-beginners] Open-ended list comprehension

[martin]

Am 03/25/2015 um 07:00 PM schrieb divyanshu ranjan:
> Hi martin,
> 
> Check dlist (https://hackage.haskell.org/package/dlist-0.7.1.1). 

I cannot see how I can create a dlist via a list comprehension, other than running fromList. But I assume this already
has o(n) complexity. It may pay after several appends, though.

What I am looking for is, if I have:

veryLongList = [x | x <- ...]

how can I use list a comprehension and end up with a dlist?




> 
> On Wed, Mar 25, 2015 at 11:21 PM, martin <martin.drautzburg at web.de <mailto:martin.drautzburg at web.de>> wrote:
> 
>     Hello all,
> 
>     when I write my own recursions, I often end up with something like
> 
>     a : b : c : (f x)
> 
>     where f x returns a list. I assume this avoids the costly (++) function, right?
> 
>     But when I use list comprehensions I always get a complete list and it is costly to append something to it. How can I
>     use the power of list comprehensions, but return an [a]->[a] instead of an [a]?
> 
>     Is this a good idea at all, or will I pile up thunks?
> 
> 
> 
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