<?php
 
$input='1+2=';
 
function calc($char=substr($input,$i=0,1),$arr=[],$signArr=[],$mem=0) {
 
	if ($i<=strlen($input)) {
		if (count($arr)<2) {
 
		if (is_numeric($char)) {
			$mem.=$char;
		} else {
			array_push($arr,$mem); 
			$mem=NULL; 
			array_push($signArr,$char);
 
		}
 
 
 
		return calc(substr($input,$i++,1),$arr,$signArr,$mem);
	}
if ($signArr[0]=='+') {
	$arr[0]=$arr[0] + $arr[1];
	$signArr[0]=$signArr[1];
 
 
 
return calc(substr($input,$i++,1),$arr,$signArr,$mem);
}
}
return $arr[0];
}
 
 
var_dump(calc());

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