Totally unrelated since I can't access the website, but one thing that I'd like to see in a typing system used in data analysis is to be able to see the dimension of the data structures used. For instance, to be able to tell at compile time if a matrix multiplication is going to crash due to dimension mismatch.

So far, in Python at least, at best I can tell that it's a float array, without specifying the dimension (for example 2d for a matrix) or better, specifying its dimension is (n,p) where n and p are both type variables.