why do you indent your code so creatively???

Right back atchya!

#!/usr/bin/perl
# http://perlmonks.org/?node_id=1148787
use strict;
use warnings;

my $total = 0.0;
my @waitlist = qw(0 200 400 800 1000);
my @fhs;

foreach my $item (@waitlist) {
    if( open my $fh, '-|' ) {
        push @fhs, $fh;
    }
    else {
        my $h = 1.0 / 1200.0;
        my $sum = 0.0;
        for my $i ($item .. $item + 200 ) {
            my $x = $h * ($i - 0.5);
            $sum += 4.0 / (1.0 + $x*$x);
        }
        my $ret=$sum * $h;
        print $ret;
        #warn "$item exiting\n";
        exit;
    }
}

for my $fh ( @fhs ) {
    $total += (<$fh> + 0.0);
    print "$total\n";
    close $fh;
}
   
print " $total\n";
print "All done!\n";
[download]

Much nicer! :)