one_source.php

<?php                                                                                                                                                                               
// ワンソース

function event() {
    $args = func_get_args();

    $name = array_shift($args);
    $callable = array_pop($args);

    $is_call = $callable();
    if($is_call) {echo $name;}
}

$weather = 'sunny';
//$weather = 'rain';

event('今日は晴れています', function() use ($weather) {
    return $weather === 'sunny';
});

event('今日は雨です', function() use ($weather) {
    return $weather === 'rain';
});

two_source01.php

<?php

function event() {
    $args = func_get_args();

    $name = array_shift($args);
    $callable = array_pop($args);

    $is_call = $callable();
    if($is_call) {echo $name;}
}

require 'two_source02.php';

two_source02.php

<?php                                                                                                                                                                               

$weather = 'sunny';
//$weather = 'rain';

event('今日は晴れています', function() use ($weather) {
    return $weather === 'sunny';
});

event('今日は雨です', function() use ($weather) {
    return $weather === 'rain';
});