General question to the list: (Q) Are there any data structures in Haskell similar to C++/STL vectors or C# generic Lists (i.e. strongly typed ArrayLists, e.g. List<int>)? These data structures grow automatically as you add elements to them (but in large chunks, not one node at a time). This data structure (if it exists in Haskell) would run inside a monad (ST and/or IO) and it would automaticly resize when needed, but would be more or less like a mutable array except you can add new elements to the end of it without reallocating an entire array of n+1 elements...
hi, to be clear, the data structure i'm thinking of is the "half edge" or "winged edge" : data structures to represent a 3d mesh in 3d modeling apps (thus, a constraint is that it can handle lot of data and fast updates).
Instead of pointers I would use integer offsets into an array of vertices. Unboxed arrays should help here. (I know when I coded a winged edge library in C++ I used indices to vertices instead of pointers, I think...) You can update mutable arrays in place (inside the ST or IO monad, of course), though I haven't had time to play with this: http://haskell.org/haskellwiki/Arrays This would be a lot more effective than lists or even doubly linked lists (mutable array access time = O(1), update time = O(1)). You could accumulate your vertices into a list and then freeze it into an array. If you need to add vertices to your array after you create it, you will need a data type like I mentioned at the (Q) above (if it exists).
the idea of creating the data structure in plain c (and maybe the basic functions) and then use it (them) in haskell is bad ?
This might be possible, but I don't think that C has the right type of data structure, either (though certainly you could create it). Ideally you want something like C++ vectors or C# generic Lists if you need the ability to augment it. If you make the datastructures and functions in C you'd still have to wrap these functions in a monad like IO to make it safe (Which the Array libs do ... if they are the right datastructure for you.) but that's probably only a good idea if you can't find the right datastruct in Haskell. Jared. -- http://www.updike.org/~jared/ reverse ")-:"