Alfonso Acosta
Actually it would maybe be better to create common high-level interface that could include unary, binary and decimal arithmetic so that the library could be easily reused in other projects (people like Bjorn, seem to be using the unary implementation). I don't know if it would be feasible though.
My reason for going with unary implementation was that it seemed to be the easiest and less tedious to implement. But is sure does make the error messages less friendly. It also limits the magnitude of the numbers quite severely unless one bumps up the type checker stack size. From the source code: "The practical size of the NumTypes is limited by the type checker stack. If the NumTypes grow too large (which can happen quickly with multiplication) an error message similar to the following will be emitted: Context reduction stack overflow; size = 20 Use -fcontext-stack=N to increase stack size to N This situation could concievably be mitigated significantly by using e.g. a binary representation of integers rather than Peano numbers." For my use (keeping track of physical dimensions) this hasn't been a problem. If Naturals had been sufficient for me I wouldn't have done my own implementation (I'm unaware of any other implementation of Integers). And there is certainly a lot of value to the clearer error messages from a decimal representation. Concerning whether or not there is any value in being able to change the representation of the type- level naturals in your library, my guess is that the value wouldn't be all that great. As I mentioned I use my implementation for tracking physical dimensions and HList's HNats for constraining vector dimensions but this isn't a problem since I cannot conceive of any reason why I would want to intermix the two. Of course, other usage scenarios exist where there would be a desire to intermix the vector dimensions with something else...? So sure, if you can abstract the representation away by all means do it. But I wouldn't go out of my way or impair the rest of the library to achieve this. Hope this helps, Bjorn