[dahart]

This is exactly right; thank you for providing the example. This is manual recursion in a heap allocated space.

If you were coding a DP problem, then custom_stack might have a fixed size you can pre-allocate, and it might also be 2 or 3-dimensional.

For some image-based recursion, your backtracking doesn’t even need to store real pointers in the stack frame. For example when I’ve written a flood fill, I can store the return pointer as a one pixel offset in as little as 2 or 3 bits, depending on whether I include diagonal pixels (4-surround vs 8-surround).