Untitled

<?php

function calculate() {
	echo 'CALCULATE' . PHP_EOL;
}

$f1 = 'calculate';

$f1();

function sum($a, $b) {
	return $a + $b;
}

function multiply($n, $m) {
	return $n * $m;
}

$f2 = 'sum';

echo 'SUM ' . $f2(10, 20) . PHP_EOL;

$f3 = 'multiply';

echo 'MUL ' . $f3(3, 4) . PHP_EOL;