Here's something that's rather crass, but maybe something like it will save you from venturing into dark regions:

c:\@Work\Perl\monks>perl -wMstrict -le
"sub working {
   my @x = (1, 0, 2);
   my @y = grep { print qq{in grep: '$_'};  return 'byebye'; } @x;
   print 'still in working(): ', qq{(@y)};
   return @y;
   }
 my @z = working;
 print qq{from working(): (@z)};
"
in grep: '1'
from working(): (byebye)

c:\@Work\Perl\monks>perl -wMstrict -le
"sub mygrep (&@) {
   my $code = shift;
   my @result;
   for (@_) {
     no warnings 'exiting';
     push(@result, $_)
       if map { print 'in map: ', qq{'$_'};  $_; } &$code;
     }
   MYGREP_FINAL:
   return @result;
   }
 ;;
 sub notworking {
   my @x = (4, 0, 3);
   my @y = mygrep {
     print qq{in mygrep: '$_'};  goto MYGREP_FINAL;
     } @x;
   print 'still in notworking(): ', qq{(@y)};
   return @y;
   }
 ;;
 my @z = notworking;
 print qq{from notworking(): (@z)};
"
in mygrep: '4'
still in notworking(): ()
from notworking(): ()
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