#!/usr/bin/perl

use strict;
use warnings;

package Range;

sub new {
    my ($class, $lower, $upper, $delta) = @_;
    bless {
        lower => $lower,
        upper => $upper,
        delta => $delta || ($upper-$lower)/1000,
        current => $lower,
    }, $class;
}

sub next {
    my $self = shift;
    ($self->{current} += $self->{delta}) < $self->{upper};
}

package main;

sub integrate {
    my ($function, $iter) = @_;
    my $sum;
    $sum += $function->($iter->{current}) * $iter->{delta} while $iter->next;
    $sum;
}

printf "%.2f\n", integrate sub {(shift)**2}, new Range (2, 5);

__END__