diff --git a/Formula1.php b/Formula1.php
index ca4d4a8..5a15474 100644
--- a/Formula1.php
+++ b/Formula1.php
@@ -2,6 +2,7 @@
 
 class Formula1 {
 	public $tree=[];
+	public $parse_error='';
 	private $dual_hp_ops = ['/','*','%','^'];
 	private $dual_lp_ops = ['+','-'];
 	private $single_ops = ['+','-'];
@@ -12,11 +13,10 @@ class Formula1 {
 		$this->precision_mode = $precision_mode;
 		$f = $this->replace_parenth($formula, 0);
 		if(strrpos($f, ')')>-1) {
-			echo('PARSING ERROR: Too many closing parenthesis !');
+			$this->parse_error = 'PARSING ERROR: Too many closing parenthesis !';
 			return(false);
 		}
 		$this->tree = $this->parse($f);
-		return(true);
 	}
 
 	private function do_single_op($op, $x){
@@ -59,7 +59,7 @@ class Formula1 {
 			if($c=='(') {
 				$closing_idx = $this->find_closingp($f, $i);
 				if($closing_idx===false) {
-					echo("PARSING ERROR: missing closing parenthesis !");
+					$this->parse_error = "PARSING ERROR: missing closing parenthesis !";
 					return('');
 				}
 				$expr = substr($f, $i+1, $closing_idx-$i-1);
@@ -76,28 +76,74 @@ class Formula1 {
 
 
 	private function parse($f){	
+//echo('<div style="font-size:12px;color:blue;">Parsing:'.$f.'</div>');		
 		$re = '/^(.+?)([\\'.implode('\\',$this->dual_lp_ops).'])(.+)$/'; // dual low priority op
 		if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-			return([$this->parse($matches[1][0]), $matches[2][0], $this->parse($matches[3][0])]);
+			$recur = $this->parse($matches[3][0]);
+			if($recur!==false) return([$this->parse($matches[1][0]), $matches[2][0], $recur]);
+			else return(false);
 		} else {
 			$re = '/^(.+?)([\\'.implode('\\',$this->dual_hp_ops).'])(.+)$/'; // dual high priority op
 			if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-				return([$this->parse($matches[1][0]), $matches[2][0], $this->parse($matches[3][0])]);
+				$recur = $this->parse($matches[3][0]);
+				if($recur!==false) return([$this->parse($matches[1][0]), $matches[2][0], $recur]);
+				else return(false);
 			} else {
 				$re = '/^([\\'.implode('\\',$this->single_ops).'])(.+)$/'; // single op
 				if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-					return([null, $matches[1][0], $this->parse($matches[2][0])]);
+					$recur = $this->parse($matches[2][0]);
+					if($recur!==false) return([null, $matches[1][0], $recur]);
+					else return(false);
 				} else {
-					$re = '/^([A-Za-z][A-Za-z0-9_]*)$/';
-					if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-						if(array_key_exists($matches[0][0], $this->params)) return($this->parse($this->params[$matches[0][0]]));
-						else echo('PARSING ERROR: Unknown expression "'.$matches[0][0].'" ');
-					} else {				
-						$re = '/^\d*(\.\d+)?$/'; // unsigned float or int
-						if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-							return($matches[0][0]);
+					$re1 = '/^([A-Za-z][A-Za-z0-9_]*)\[\"([A-Za-z0-9_]+)\"\]$/'; // arrays with alphanum keys
+					$re2 = "/^([A-Za-z][A-Za-z0-9_]*)\[\'([A-Za-z0-9_]+)\'\]$/"; // arrays with alphanum keys
+					if(preg_match($re1, $f, $matches1, PREG_OFFSET_CAPTURE, 0)||preg_match($re2, $f, $matches2, PREG_OFFSET_CAPTURE, 0)){ 
+						$array_name = (count($matches1)>0) ? $matches1[1][0] : $matches2[1][0];
+						$array_key = (count($matches1)>0) ? $matches1[2][0] : $matches2[2][0];
+						if(array_key_exists($array_name, $this->params) && is_array($this->params[$array_name])) {
+							if(array_key_exists($array_key, $this->params[$array_name])) {
+								return($this->parse($this->params[$array_name][$array_key]));
+							} else {
+								$this->parse_error = 'PARSING ERROR: Unknown key "'.$array_key.'" for array "'.$array_name.'" ';
+								return(false);
+							}
 						} else {
-							echo('PARSING ERROR at '.$f.'<br/>');
+							$this->parse_error = 'PARSING ERROR: Unknown array "'.$array_name.'" ';
+							return(false);
+						}
+					} else {
+						$re = '/^([A-Za-z][A-Za-z0-9_]*)\[(\d+)\]$/'; // arrays with alphanum keys
+						if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
+							$array_name = $matches[1][0];
+							$array_index = $matches[2][0];
+							if(array_key_exists($array_name, $this->params) && is_array($this->params[$array_name])) {
+								if(isset($this->params[$array_name][$array_index])) {
+									return($this->parse($this->params[$array_name][$array_index]));
+								} else {
+									$this->parse_error = 'PARSING ERROR: Unknown index "'.$array_index.'" for array "'.$array_name.'" ';
+									return(false);
+								}
+							} else {
+								$this->parse_error = 'PARSING ERROR: Unknown array "'.$array_name.'" ';
+								return(false);
+							}
+						} else {
+							$re = '/^([A-Za-z][A-Za-z0-9_]*)$/'; // simple variables
+							if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
+								if(array_key_exists($matches[0][0], $this->params)) return($this->parse($this->params[$matches[0][0]]));
+								else {
+									$this->parse_error = 'PARSING ERROR: Unknown expression "'.$matches[0][0].'" ';
+									return(false);
+								}
+							} else {				
+								$re = '/^\d*(\.\d+)?$/'; // unsigned float or int
+								if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
+									return($matches[0][0]);
+								} else {
+									$this->parse_error = 'PARSING ERROR at '.$f.'<br/>';
+									return(false);
+								}
+							}
 						}
 					}
 				}