sub no_bindings
{
	return not keys %{$_[0]};
}


sub is_variable
{
	return substr($_[0], 0, 1) eq '?';
}


sub get_binding
{
	my ($var, $bind) = @_;	
	defined($bind->{$var}) ? [$var, $bind->{$var}] : undef;
}


sub binding_val
{
	defined($_[0]) ? $_[0]->{1} : undef;
}


sub lookup
{
	my ($var, $bind) = @_;
	return $bind->{$var};
}


sub extend_bindings
{
	my ($var, $val, $bind) = @_;
	$bind->{$var} = $val;
	return $bind;
}