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<?php $f = function($x) use($f){ if($x==0 || $x==1) return 1; return $f($x-1) + $f($x-2); }; print $f(10);
Output for 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
Warning: Undefined variable $f in /in/cO2ER on line 3 Fatal error: Uncaught Error: Value of type null is not callable in /in/cO2ER:6 Stack trace: #0 /in/cO2ER(9): {closure}(10) #1 {main} thrown in /in/cO2ER on line 6
Process exited with code 255.
Output for 7.0.0 - 7.0.20, 7.1.0 - 7.1.25, 7.2.0 - 7.2.33, 7.3.0 - 7.3.31, 7.4.0 - 7.4.25, 7.4.27 - 7.4.33
Notice: Undefined variable: f in /in/cO2ER on line 3 Fatal error: Uncaught Error: Function name must be a string in /in/cO2ER:6 Stack trace: #0 /in/cO2ER(9): {closure}(10) #1 {main} thrown in /in/cO2ER on line 6
Process exited with code 255.
Output for 7.3.32 - 7.3.33, 7.4.26
Fatal error: Uncaught Error: Function name must be a string in /in/cO2ER:6 Stack trace: #0 /in/cO2ER(9): {closure}(10) #1 {main} thrown in /in/cO2ER on line 6
Process exited with code 255.
Output for 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.24 - 5.5.35, 5.6.8 - 5.6.28
Notice: Undefined variable: f in /in/cO2ER on line 3 Fatal error: Function name must be a string in /in/cO2ER on line 6
Process exited with code 255.
Output for 4.4.2 - 4.4.9, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17
Parse error: syntax error, unexpected T_FUNCTION in /in/cO2ER on line 3
Process exited with code 255.
Output for 4.3.0 - 4.3.1, 4.3.5 - 4.3.11, 4.4.0 - 4.4.1, 5.0.0 - 5.0.5
Parse error: parse error, unexpected T_FUNCTION in /in/cO2ER on line 3
Process exited with code 255.
Output for 4.3.2 - 4.3.4
Parse error: parse error in /in/cO2ER on line 3
Process exited with code 255.

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