[Haskell-cafe] Re: Infinite grid

[ChrisK]

Luke Palmer wrote:
> On Mon, Dec 29, 2008 at 3:55 PM, Martijn van Steenbergen 
> <martijn at van.steenbergen.nl <mailto:martijn at van.steenbergen.nl>> wrote:
> 
>     Hello,
> 
>     I would like to construct an infinite two-dimensional grid of nodes,
>     where a node looks like this:
> 
>         data Node = Node
>          { north :: Node
>          , east  :: Node
>          , south :: Node
>          , west  :: Node
>          }
> 
> 
>     in such a way that for every node n in the grid it doesn't matter
>     how I travel to n, I always end up in the same memory location for
>     that node.
> 
> 
> No problem:
> 
> let n = Node n n n n in n
> 
> But you probably want some additional data in each node, also, in which 
> the problem becomes harder.

The solution very much depends on how the data is initialized / computed / obtained.

Note that one can put an IORef into the Node to allow for mutable value.

Also, see if you need something akin to mkDList at 
http://haskell.org/haskellwiki/Tying_the_Knot

Cheers,
   Chris