=usage
    reduce \&f @x;
eg.
    reduce {$a+$b} @x;		# sum @x
    reduce {$a*$b) 1..7		# factorial(7) = 7!
=cut

sub reduce (&@)
{ my $f = shift;
  local ($a, $b) = shift;
  $a=&$f while $b=shift;
  return $a;
}

my $x = reduce { $a*$b } 1..7;
print $x;