Are you thinking of Agda/Coq/Idris, which have dependent types? If you understand a bit of type theory, this is an interesting paper: http://www.cs.cmu.edu/~fp/

Are you thinking of Agda/Coq/Idris, which have dependent types? If you understand a bit of type theory, this is an interesting paper: http://www.cs.cmu.edu/~fp/papers/popl99.pdf http://www.cs.cmu.edu/~fp/papers/popl99.pdf