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<?php function is_even(int $n): bool { $fn = null; $fn = static function(int $nr) use($fn): bool { if ($nr < 0) { $nr = abs($nr); } if ($nr === 0) { return true; } return $fn($nr - 1); }; return $fn($n, false); } for($i = -5; $i <= 12; $i++) { printf('is %d even? %s.%s', $i, is_even($i) ? 'yes': 'no', "\n"); }
based on Xtabs
Output for 8.0.0alpha1 - alpha3
Fatal error: Uncaught Error: Value of type null is not callable in /in/2afJ5:14 Stack trace: #0 /in/2afJ5(17): {closure}(5, false) #1 /in/2afJ5(21): is_even(-5) #2 {main} thrown in /in/2afJ5 on line 14
Process exited with code 255.
Output for 7.2.0 - 7.2.32, 7.3.0 - 7.3.20, 7.4.0 - 7.4.8
Fatal error: Uncaught Error: Function name must be a string in /in/2afJ5:14 Stack trace: #0 /in/2afJ5(17): {closure}(5, false) #1 /in/2afJ5(21): is_even(-5) #2 {main} thrown in /in/2afJ5 on line 14
Process exited with code 255.