Repulsion-Force (Colomb's Law)

gistfile1.php

#!/usr/bin/env php
<?php

# From: http://www.reddit.com/r/dailyprogrammer/comments/1ml669/091713_challenge_138_easy_repulsionforce/

function calculate_repulsion_force($mass1, $mass2, $distance) {
    $divisor = bcmul($mass1, $mass2);
    $dividend = bcpow($distance, 2);
    return bcdiv($divisor, $dividend);
}

function calculate_distance($x1, $y1, $x2, $y2) {
    # sqrt((x1 - x2)^2 + (y1 - y2)^2)
    $dx = bcsub($x1, $x2); # x1 - x2
    $dy = bcsub($y1, $y2); # y1 - y2
    $x2 = bcpow($dx, '2'); # dx ^ 2
    $y2 = bcpow($dy, '2'); # dy ^ 2
    $sum = bcadd($x2, $y2); # x2 + y2
    return bcsqrt($sum);
}

function get_input($prompt) {
    $are_numeric = function () {
        # If the array is empty, all values were numeric, returns true.
        return !array_filter(func_get_args(), function ($n) {
            return !is_numeric($n);
        });
    };
    # I read these as strings instead of floats
    # so they can be larger than the max float value.
    print $prompt;
    $count = fscanf(STDIN, "%s %s %s", $mass, $posx, $posy);
    if (3 !== $count || !$are_numeric($mass, $posx, $posy)) {
        print "Incorrect input format.\n";
        return get_input($prompt);
    }
    return [$mass, $posx, $posy];
}

# Set bcmath precision scale to 5
bcscale(5);

list($mass1, $x1, $y1) = get_input("Please enter the first particle as [mass] [pos-x] [pos-y]: ");
list($mass2, $x2, $y2) = get_input("Please enter the second particle as [mass] [pos-x] [pos-y]: ");

$distance = calculate_distance($x1, $y1, $x2, $y2);
if ($distance == '0') {
    exit("The distance between the given particles is zero.\n");
}
$force = calculate_repulsion_force($mass1, $mass2, $distance);
print "Calculated repulsion force: $force\n";