Definitions are allowed to have free variables

[bmsherman]

This shouldn't typecheck

type Random A = integer -> integer * A;;
let runRandom (x : Random A) : A =
  (x i0)[1];;

because the A in runRandom is unbound.

let runRandom A (x : Random A) : A =
  (x i0)[1];;

[bmsherman]

This results in typechecking errors further down the line.