package main;

my %par;
tie(%par,'ParamsHash');

print "Initial values:\n";
printSomeParams();

print "Setting 'margin' to 4:\n";
$par{margin}=4;
printSomeParams();

print "Setting 'margin-horizontal' to 8:\n";
$par{'margin-horizontal'}=8;
printSomeParams();

print "Setting 'margin-left' to 3:\n";
$par{'margin-left'}=3;
printSomeParams();

sub printSomeParams {
  map {printParam($_)} (qw'
                        margin
                        margin-horizontal
                        margin-left
                        margin-right
                        ')
}

sub printParam { print "  $_[0] = $par{$_[0]}\n" }