anonymous recursion in php

closure-by-reference.php

<?php
$fibonacci = function( $n ) use ( &$fibonacci ) {
	return ( $n < 2 ) ? $n : ( $fibonacci( $n - 1 ) + $fibonacci( $n - 2 ) );
};
echo $fibonacci(4); // Outputs "3" (0,1,1,2,3)

map.php

<?php
function map( $f, array $seq, array $mapped = array() ) {
	if( !empty( $seq ) ) $mapped[] = $f( reset( $seq ) );
	return !empty( $seq ) ? map( $f, array_slice( $seq, 1 ), $mapped ) : $mapped;
}
print_r( map( $fibonacci, range( 1, 5 ) ) ); // Maps integers to Fibs

naive-closure-approach.php

<?php
$fibonacci = function( $n ) use ( $fibonacci ) {
	return ( $n < 2 ) ? $n : ( $fibonacci( $n - 1 ) + $fibonacci( $n - 2 ) );
};
echo $fibonacci(4); // Fatal error: Function name must be a string

php-library-map.php

<?php
print_r( array_map( $fibonacci, range( 1, 5 ) ) ); // Maps integers to Fibs

php-library-reduce.php

<?php
echo array_reduce( array_map( $fibonacci, range( 1, 5 ) ), function($a,$b){ return $a+$b; }, 0 ); // Outputs 12

reduce.php

<?php
function reduce( $f, array $seq, $s = 0 ) {
	$s = !empty( $seq ) ? $f( $s, reset( $seq ) ) : $s;
	return !empty( $seq ) ? reduce( $f, array_slice( $seq, 1 ), $s ) : $s;
}

echo reduce( function($a,$b){ return $a+$b; }, map( $fibonacci, range( 1, 5 ) ), 0 ); // Outputs 12

super-naive-approach.php

<?php
$fibonacci = function( $n ) { 
	return ( $n < 2 ) ? $n : ( $fibonacci( $n - 1 ) + $fibonacci( $n - 2 ) );
};
echo $fibonacci(4); // should be (0,1,2,3,4) -> (0,1,1,2,3)