<?php function Y ($le) {return (function ($f) {return $f($f); })(function ($f) use ($le) {return $le(function ($x) use ($f) {return $f($f)($x); }); }); } $le = function ($factorial) {return function ($n) use ($factorial) {return $n < 2 ? $n : $n * $factorial($n - 1); }; }; $factorial = Y($le); echo $factorial(1) . PHP_EOL; // 1 echo $factorial(2) . PHP_EOL; // 2 echo $factorial(5) . PHP_EOL; // 120
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