Re: Representing cyclic data structures efficiently in Haskell

G'day all. As you note, some kind of indirection is what you want here. On Mon, Jul 07, 2003 at 04:04:17PM +0100, Sarah Thompson wrote:

I would also need to implement efficient indexes into the data structure -- flat searching will be too slow for non-trivial amounts of data. In C++, I'd implement one or more external (probably STL-based) indexes that point into the main data structure.

The direct Haskell equivalent is to use Refs; either IORefs or STRefs. (I'd personally use IORefs, but that's because I like having IO around.) Dereferencing an IORef is a constant-time operation, just like chasing a pointer in C. Cheers, Andrew Bromage