Note that:
call(Goal) is logically the same as Goal and !/0 does not cut through call/1.
Success:
      [eclipse]: [user].
       or(A -> B, C) :- call(A), !, call(B).
       or(_ -> _, C) :- call(C).
       user compiled 412 bytes in 0.02 seconds
      [eclipse]: or(write(a)->fail, write(k)).
      a
      no.
      [eclipse]: or(fail->write(here),true).
      yes.
Fail:
      [eclipse]: call(fail),write(here).
      no.
Error:
      call(G).                  (Error 4).
      call("write(a)").         (Error 5).