ring TC not working

Stream: new members

[Yakov Pechersky]

Why does the second example here not work?

import tactic.ring_exp

example (a b : ℤ) : (a + b) * (a - b) = a ^ 2 - b ^ 2 :=
begin
  ring_exp
end

example {R : Type*} [ring R] (a b : R) : (a + b) * (a - b) = a ^ 2 - b ^ 2 :=
begin
  ring_exp
end

[Yakov Pechersky]

In widgets, clicking on ring gives no information.

[Yakov Pechersky]

Ah, I need comm_ring for the latter to work.