$a = sub {return @_[0]}; (yes I know....)
$b = sub {return @_[0]+1};

.... some code .....
if (something)
   $i = $a;
else
   $i = $b;

&lala ($i);

sub lala{
   my $i = $_[0];
   $res = &{$i}($number) ;
   #have also tried $res = $i->($number) with the same result
}