$ perl -wMstrict -le 'sub foo { print wantarray?"list":"scalar";
  return (0); }; if(foo) {print "true"} else {print "false"} '
scalar
false
$ perl -wMstrict -le 'sub foo { print wantarray?"list":"scalar";
  return (0); }; if(()=foo) {print "true"} else {print "false"} '
list
true
$ perl -wMstrict -le 'sub foo { print wantarray?"list":"scalar";
  return (0); }; my @x=foo;if(@x) {print "true"} else {print "false"}'
list
true