#I have some variables, and some ranges.
#really it's in a tied hash somewhere.

my %hash = {  #pretend that this is my tied hash
    a => "20",
    b => "yes",
    q => "1e-14"
};
my @range_a = (1..20);
my @range_b = ("yes", "no");

#each variable of interest has a foreach loop
# to go through the values in it's range
foreach my $a (@range_a){
  $hash{a} = $a;

  #other variables may be involved.
  my $seed = srand($a + 42); 
  my $randomness = rand($seed); 
  #or a function
  func_1(%hash);

  foreach my $b (@range_b){
    $hash{b} = $b;
    my $foo = $b + $a;

    #Then, at the innermost level, do something
    #There could be any number (probably below 20)
    # of these loops.
    my $result = end_func(%hash);
  }
}