[sf-perl] a reason to goto

Joe Brenner doom at kzsu.stanford.edu
Sat Feb 24 23:25:23 PST 2007

David Alban wrote:

> What about making a subroutine out of it, to which you pass $REFLEXIVE (and
> maybe $i and $j)?  If after calling pick_numeric( ... ) $REFLEXIVE doesn't
> have the value you want, you recursively call the subroutine?  I know some
> folks don't like recursion, and if you anticipate a large number of
> recursive calls it could be a performance issue, but I thought I'd ask.

I don't have any particular dislike of recursion [1] -- except that I find
that it *still* takes me forever to debug recursive code -- but I
probably wouldn't resort to it for something like this.  The code as 
written strikes me as fairly straight-forward, it's just that perl's 
quirks were getting in the way of getting it working. 

In case it's not clear, the idea is simply that I want to randomly
choose two integers, but under normal conditions I'd rather that 
they not be the same numbers (however if $REFLEXIVE is set, then 
two identical picks are okay).  

I don't know if it made it out to the list (I think my mail is acting
flaky at the moment) but the perlish way of doing it is probably this:

   if ($RANDOMIZE) {
       $i = pick_numeric(0, $numb_cards-1);
       $j = pick_numeric(0, $numb_cards-1);
       unless( $REFLEXIVE ) {
         if ($i == $j) {

Though if "pick_numeric" were an expensive function, I might prefer
not to redo both picks, and I'd go for *something* like this:

   if ($RANDOMIZE) {
       $i = pick_numeric(0, $numb_cards-1);
       do { 
          $j = pick_numeric(0, $numb_cards-1);       
       } until ($j != $i) || ($REFLEXIVE);

[1] As for worrying about disk thrashing: it's not particuarly difficult
to use a counter to error out if you've exceeded 10000 levels of recursion
or so. 

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