title: How did Fortran prevent recursion prior to Fortran 90?
body: <p>I have been reading a bit about programming languages and saw that prior to Fortran 90 recursion was not permitted. How was indirect recursion prevented?</p>
  <p>While I see how direct recursion (inside the body of the function itself) can be trivially detected, the problem seems much harder in the general case.</p>