David Lo writes:
[[Int]] to int[][]
Pardon me if I'm telling you something you already know, but I wanted to make sure you are aware of it. int[][] is a very different type than [[Int]] is. An int[][] is a pointer to an array of pointers to integers: int[][] <==> int*[] <==> int** Now think of the following Haskell list: [ [ 1, 2, 3, 4] , [ 1 ] , [ 1, 2 ] ] C can't easily express that because an array in C does not have a length -- a list in Haskell, however, does. To understand the difference, just ask yourself what the element my_list[1][3] would be. In the Haskell type, this element does not exist: The second list has only one element. Only, C doesn't know that! It will simply translate the expression to: *( *(my_list + 1) + 3 ) And give you the contents of any random memory location, thus, almost certainly crashing your program. Which is why C sucks and Haskell rules. :-) My point is: marshaling a nested list is really not as simple as it looks and int[][] is almost certainly not the right type to marshal to. You'd need something that contains the information which element list is how long, something like: struct integer_list { size_t len; int* elements; } struct nested_list { size_t len; integer_list* elements } What _exactly_ you would need, though, is impossible to say without understanding what you are trying to do. And explaining all this would probably be too complex to do it casually on a public mailing list. I hope this helps somewhat. And I hope I remembered the order in which C does resolve the int[][] type correctly. I could never get that right. I hope someone corrects me, should it be wrong. Peter