>> You're missing the point.  Suppose Erann and I were working on some
>> project and he had written the above macro.  I don't have to know
>> the details of implementation (I'm assuming that I can trust Erann
>> not to write bogus code).  Using the macro is *far* preferable to
>> something like:

>>      (start-reactor)
>>      (when (< minval (reactor-temp) maxval)
>>         (scram))
>>      (while (true)
>>         (operate-reactor-step))
>>         (when (< minval (reactor-temp) maxval)
>>            (scram))
>>      (shutdown-reactor)

>> Especially because there is a non-obvious bug in the above code.

> Not obvious to you or me maybe. But Emacs Knows(tm). ;-)