Given vectors u = (u1, u2 ,..., un) and v = (v1, v2 ,..., vn), the inner product of u and v is defined to be u1*v1 + u2*v2 + ... + un*vn. Write a curried F# function inner that takes two vectors represented as int lists and returns their inner product (assuming the two lists are of equal length):

> inner [1;2;3] [4;5;6];;

val it : int = 32