[Haskell-cafe] Re: Infinite grid

Luke Palmer wrote:

On Mon, Dec 29, 2008 at 3:55 PM, Martijn van Steenbergen mailto:martijn@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