Does this changed version of your code still do what you need? [https://play.nim-lang.org/#ix=25Fy](https://play.nim-lang.org/#ix=25Fy)
I found that you don't need the extra type parameters around your solve iterator: T and V are already coming from `allExactCover`. You may also need to look at how you are creating your HashSet `c`; the creation proc needs to know the type (`[V]`). Good luck!
