My impression of the sample programs is that they're unreadably noisy, but maybe this would be a good compiler target if you're writing your own language?
How would you write https://github.com/tspader/sp/blob/main/example/ls.c in your statically typed language of choice? To be fair, this is definitely the kindest example to my library, but one reason I felt this project was worth pursuing was that that example reads basically like a slightly worse TypeScript to me. In other words, quite nice for how low level the code really is.
Because it's const void *pa, you don't need the cast. A void * pointer will convert to any other kind of pointer. Now you only need to mention the type once. (I forget the const-related rules, but since the consts match in this case I don't think it'll be relevant.)